Name

sqitchtutorial-snowflake - A tutorial introduction to Sqitch change management on Snowflake

Synopsis

  sqitch *

Description

This tutorial explains how to create a sqitch-enabled Snowflake project, use a VCS for deployment planning, and work with other developers to make sure changes remain in sync and in the proper order.

We'll start by creating a new project from scratch, a fictional antisocial networking site called Flipr. All examples use Git <https://git-scm.com/> as the VCS and Snowflake <https://www.snowflake.net/> as the storage engine, but for the most part you can substitute other VCSes and database engines in the examples as appropriate.

If you'd like to manage a PostgreSQL database, see sqitchtutorial.

If you'd like to manage an SQLite database, see sqitchtutorial-sqlite.

If you'd like to manage an Oracle database, see sqitchtutorial-oracle.

If you'd like to manage a MySQL database, see sqitchtutorial-mysql.

If you'd like to manage a Firebird database, see sqitchtutorial-firebird.

If you'd like to manage a Vertica database, see sqitchtutorial-vertica.

If you'd like to manage an Exasol database, see sqitchtutorial-exasol.

  [Snowflake]
  Description = ODBC for Snowflake
  Driver      = /usr/lib64/snowflake/odbc/lib/libSnowflake.so

Starting a New Project

Usually the first thing to do when starting a new project is to create a source code repository. So let's do that with Git:

  > mkdir flipr
  > cd flipr
  > git init .
  Initialized empty Git repository in /flipr/.git/
  > touch README.md
  > git add .
  > git commit -am 'Initialize project, add README.'

If you're a Git user and want to follow along the history, the repository used in these examples is on GitHub <https://github.com/sqitchers/sqitch-snowflake-intro>.

Now that we have a repository, let's get started with Sqitch. Every Sqitch project must have a name associated with it, and, optionally, a unique URI. We recommend including the URI, as it increases the uniqueness of object identifiers internally, and will prevent the deployment of a different project with the same name. So let's specify one when we initialize Sqitch:

  > sqitch init flipr --uri https://github.com/sqitchers/sqitch-snowflake-intro/ --engine snowflake
  Created sqitch.conf
  Created sqitch.plan
  Created deploy/
  Created revert/
  Created verify/

Let's have a look at sqitch.conf:

  > cat sqitch.conf
  [core]
    engine = snowflake
    # plan_file = sqitch.plan
    # top_dir = .
  # [engine "snowflake"]
    # target = db:snowflake:
    # registry = sqitch
    # client = snowsql

Good, it picked up on the fact that we're creating changes for the Snowflake engine, thanks to the "--engine snowflake" option, and saved it to the file. Furthermore, it wrote a commented-out "[engine "snowflake"]" section with all the available Snowflake engine-specific settings commented out and ready to be edited as appropriate.

By default, Sqitch will read sqitch.conf in the current directory for settings. But it will also read ~/.sqitch/sqitch.conf for user-specific settings. Since Snowflake's "snowsql" client is not in the path on my system, let's go ahead an tell it where to find the client on our computer (don't bother if you're using the Docker image <https://hub.docker.com/r/sqitch/sqitch/> because it uses the client inside the container, not on your host machine):

  > sqitch config --user engine.snowflake.client /Applications/SnowSQL.app/Contents/MacOS/snowsql

And let's also tell it who we are, since this data will be used in all of our projects:

  > sqitch config --user user.name 'Marge N. OXVera'
  > sqitch config --user user.email 'marge@example.com'

Have a look at ~/.sqitch/sqitch.conf and you'll see this:

  > cat ~/.sqitch/sqitch.conf
  [engine "snowflake"]
    client = /Applications/SnowSQL.app/Contents/MacOS/snowsql
  [user]
    name = Marge N. OXVera
    email = marge@example.com

Which means that Sqitch should be able to find "snowsql" for any project, and that it will always properly identify us when planning and committing changes.

Back to the repository. Have a look at the plan file, sqitch.plan:

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/sqitchers/sqitch-snowflake-intro/

Note that it has picked up on the name and URI of the app we're building. Sqitch uses this data to manage cross-project dependencies. The "%syntax-version" pragma is always set by Sqitch, so that it always knows how to parse the plan, even if the format changes in the future.

Let's commit these changes and start creating the database changes.

  > git add .
  > git commit -am 'Initialize Sqitch configuration.'
  [main b731cc3] Initialize Sqitch configuration.
   2 files changed, 15 insertions(+)
   create mode 100644 sqitch.conf
   create mode 100644 sqitch.plan

Our First Change

First, our project will need a schema. This creates a nice namespace for all of the objects that will be part of the flipr app. Run this command:

  > sqitch add appschema -n 'Add schema for all flipr objects.'
  Created deploy/appschema.sql
  Created revert/appschema.sql
  Created verify/appschema.sql
  Added "appschema" to sqitch.plan

The "add" command adds a database change to the plan and writes deploy, revert, and verify scripts that represent the change. Now we edit these files. The "deploy" script's job is to create the schema. So we add this to deploy/appschema.sql:

  CREATE SCHEMA flipr;

The "revert" script's job is to precisely revert the change to the deploy script, so we add this to revert/appschema.sql:

  DROP SCHEMA flipr;

Now we can try deploying this change. We tell Sqitch where to send the change via a database URI <https://github.com/libwww-perl/uri-db/>. Let's say we're using the account name "example", username "movera", database "flipr", and warehouse "sqitch", and an ODBC driver named "Snowflake" (see "Connection Configuration" for details). The URI would be structured like this:

  db:snowflake://movera@example/flipr?Driver=Snowflake;warehouse=sqitch

Note that Sqitch requires a "warehouse" parameter in order to record its work in the registry. The default warehouse is named "sqitch", so you can omit it from the URI if that's the warehouse you want Sqitch to use (we'll omit it for the remainder of this tutorial). Otherwise, specify it in the URI. Snowflake also requires a password, which could also be included in the URI, but it's best to put it in the "connections" section of the .snowsql/config file <https://docs.snowflake.com/en/user-guide/snowsql-start.html#configuring-default-connection-settings>. See sqitch-authentication for details.

We just tell Sqitch to use that URI to deploy the change:

  > sqitch deploy 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Adding registry tables to db:snowflake://movera@example/flipr?Driver=Snowflake
  Deploying changes to db:snowflake://movera@example/flipr?Driver=Snowflake
    + appschema .. ok

First Sqitch created registry tables used to track database changes. The structure and name of the registry varies between databases (Snowflake uses a schema to namespace its registry, while SQLite and MySQL use separate databases). Next, Sqitch deploys changes. We only have one so far; the "+" reinforces the idea that the change is being "added" to the database.

Note that this process can take quite a bit of time. Sqitch connects to the database via ODBC and retains the connection throughout, but the creation of the registry and all change scripts run through individual runs of "snowsql". These connections can be quite slow. So if Sqitch seems hung, just wait; it's most likely waiting on Snowflake.

With this change deployed, if you connect to the database, you'll be able to see the schema:

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE SCHEMAS LIKE 'flipr'"
  +-------------------------------+-------+------+---------------+-------------+
  | created_on                    | name  | kind | database_name | schema_name |
  |-------------------------------+-------+------+---------------+-------------|
  | 2018-07-27 14:47:22.614 +0000 | FLIPR | NULL | DWHEELER      | NULL        |
  +-------------------------------+-------+------+---------------+-------------+
  1 Row(s) produced. Time Elapsed: 0.283s

  CREATE TEMPORARY TABLE flipr.verify__ (id INT);

  USE WAREHOUSE &warehouse;
  SELECT 1/COUNT(*) FROM information_schema.schemata WHERE schema_name = 'FLIPR';

  > sqitch verify 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Verifying db:snowflake://movera@example/flipr?Driver=Snowflake
    * appschema .. ok
  Verify successful

  CREATE TEMPORARY TABLE nonesuch.verify__ (id INT);

  > sqitch verify 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Verifying db:snowflake://movera@example/flipr?Driver=Snowflake
  * appschema ..
  002003 (02000): SQL compilation error:
  Schema 'FLIPR.NONESUCH' does not exist.
  # Verify script "verify/appschema.sql" failed.
  not ok
  Verify Summary Report
  ---------------------
  Changes: 1
  Errors:  1
  Verify failed

  USE WAREHOUSE &warehouse;
  SELECT 1/COUNT(*) FROM information_schema.schemata WHERE schema_name = 'NONESUCH';

  > sqitch verify 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Verifying db:snowflake://movera@example/flipr?Driver=Snowflake
  * appschema ..
  100051 (22012): Division by zero
  # Verify script "verify/appschema.sql" failed.
  not ok
  Verify Summary Report
  ---------------------
  Changes: 1
  Errors:  1
  Verify failed

  > sqitch status 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  # On database db:snowflake://movera@example/flipr?Driver=Snowflake
  # Project:  flipr
  # Change:   5a2ac4ae6801bfe392483ee5912b4e3592cdd57a
  # Name:     appschema
  # Deployed: 2018-07-27 10:47:23 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

  > sqitch revert 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Revert all changes from db:snowflake://movera@example/flipr?Driver=Snowflake? [Yes]
    - appschema .. ok

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE SCHEMAS LIKE 'flipr'"
  +------------+------+------+---------------+-------------+
  | created_on | name | kind | database_name | schema_name |
  |------------+------+------+---------------+-------------|
  +------------+------+------+---------------+-------------+
  0 Row(s) produced. Time Elapsed: 0.204s

  > sqitch status 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  # On database db:snowflake://movera@example/flipr?Driver=Snowflake
  No changes deployed

  > sqitch verify 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Verifying db:snowflake://movera@example/flipr?Driver=Snowflake
  No changes deployed

  > sqitch log 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  On database db:snowflake://movera@example/flipr?Driver=Snowflake
  Revert 5a2ac4ae6801bfe392483ee5912b4e3592cdd57a
  Name:      appschema
  Committer: Marge N. OXVera <marge@example.com>
  Date:      2018-07-27 10:48:48 -0400
      Add schema for all flipr objects.
  Deploy 5a2ac4ae6801bfe392483ee5912b4e3592cdd57a
  Name:      appschema
  Committer: Marge N. OXVera <marge@example.com>
  Date:      2018-07-27 10:47:24 -0400
      Add schema for all flipr objects.

  > git add .
  > git commit -m 'Add flipr schema.'
  [main 7fd5ace] Add flipr schema.
  4 files changed, 10 insertions(+)
  create mode 100644 deploy/appschema.sql
  create mode 100644 revert/appschema.sql
  create mode 100644 verify/appschema.sql

  > sqitch deploy --verify 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  Deploying changes to db:snowflake://movera@example/flipr?Driver=Snowflake
    + appschema .. ok

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE SCHEMAS LIKE 'flipr'"
  +-------------------------------+-------+------+---------------+-------------+
  | created_on                    | name  | kind | database_name | schema_name |
  |-------------------------------+-------+------+---------------+-------------|
  | 2018-07-27 14:52:50.116 +0000 | FLIPR | NULL | DWHEELER      | NULL        |
  +-------------------------------+-------+------+---------------+-------------+
  1 Row(s) produced. Time Elapsed: 0.283s

  > sqitch status 'db:snowflake://movera@example/flipr?Driver=Snowflake'
  # On database db:snowflake://movera@example/flipr?Driver=Snowflake
  # Project:  flipr
  # Change:   5a2ac4ae6801bfe392483ee5912b4e3592cdd57a
  # Name:     appschema
  # Deployed: 2018-07-27 10:52:54 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

On Target

I'm getting a little tired of always having to type "db:snowflake://movera@example/flipr?Driver=Snowflake", aren't you? This database connection URI <https://github.com/libwww-perl/uri-db/> tells Sqitch how to connect to the deployment target, but we don't have to keep using the URI. We can name the target:

  > sqitch target add flipr_test 'db:snowflake://movera@example/flipr?Driver=Snowflake'

The "target" command, inspired by "git-remote" <https://git-scm.com/docs/git-remote>, allows management of one or more named deployment targets. We've just added a target named "flipr_test", which means we can use the string "flipr_test" for the target, rather than the URI. But since we're doing so much testing, we can also tell Sqitch to deploy to the "flipr_test" target by default:

  > sqitch engine add snowflake flipr_test

Now we can omit the target argument altogether, unless we need to deploy to another database. Which we will, eventually, but at least our examples will be simpler from here on in, e.g.:

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   5a2ac4ae6801bfe392483ee5912b4e3592cdd57a
  # Name:     appschema
  # Deployed: 2018-07-27 10:52:54 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

Yay, that allows things to be a little more concise. Let's also make sure that changes are verified after deploying them:

  > sqitch config --bool deploy.verify true
  > sqitch config --bool rebase.verify true

We'll see the "rebase" command a bit later. In the meantime, let's commit the new configuration and and make some more changes!

  > git commit -am 'Set default deployment target and always verify.'
  [main 3834a8d] Set default deployment target and always verify.
   1 files changed, 8 insertions(+), 0 deletions(-)

Deploy with Dependency

Let's add another change, this time to create a table. Our app will need users, of course, so we'll create a table for them. First, add the new change:

  > sqitch add users --requires appschema -n 'Creates table to track our users.'
  Created deploy/users.sql
  Created revert/users.sql
  Created verify/users.sql
  Added "users [appschema]" to sqitch.plan

Note that we're requiring the "appschema" change as a dependency of the new "users" change. Although that change has already been added to the plan and therefore should always be applied before the "users" change, it's a good idea to be explicit about dependencies.

Now edit the scripts. When you're done, deploy/users.sql should look like this:

  -- Deploy flipr:users to snowflake
  -- requires: appschema
  USE WAREHOUSE &warehouse;
  CREATE TABLE flipr.users (
      nickname  TEXT         PRIMARY KEY,
      password  TEXT         NOT NULL,
      fullname  TEXT         NOT NULL,
      twitter   TEXT         NOT NULL,
      timestamp TIMESTAMP_TZ NOT NULL DEFAULT CURRENT_TIMESTAMP
  );

A few things to notice here. On the second line, the dependence on the "appschema" change has been listed. This doesn't do anything, but the default "deploy" Snowflake template lists it here for your reference while editing the file. Useful, right?

The table itself will be created in the "flipr" schema. This is why we need to require the "appschema" change.

On the fourth line, the "USE WAREHOUSE" statement was inserted by the default Snowflake template. We don't actually need it to create a table, but there's no harm in leaving it here.

Now for the verify script. The simplest way to check that the table was created and has the expected columns without touching the data? Just select from the table with a false "WHERE" clause. Here the "USE WAREHOUSE" statement is required so that the "SELECT" statement can actually execute. Probably easiest just to leave the default, which uses the warehouse that Sqitch uses to maintain its registry. Edit verify/users.sql to look like this:

  USE WAREHOUSE &warehouse;
  SELECT nickname, password, fullname, twitter, timestamp
    FROM flipr.users
  WHERE FALSE;

Now for the revert script: all we have to do is drop the table. Add this to revert/users.sql:

  DROP TABLE flipr.users;

Couldn't be much simpler, right? Let's deploy this bad boy:

  > sqitch deploy
  Deploying changes to flipr_test
    + users .. ok

We know, since verification is enabled, that the table must have been created. But for the purposes of visibility, let's have a quick look:

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE TABLES LIKE 'users' IN flipr"
  +-------------------------------+-------+-------+---------------+-------------+
  | created_on                    | name  | kind  | database_name | schema_name |
  |-------------------------------+-------+-------+---------------+-------------|
  | 2018-07-27 15:13:21.767 +0000 | USERS | TABLE | DWHEELER      | FLIPR       |
  +-------------------------------+-------+-------+---------------+-------------+
  1 Row(s) produced. Time Elapsed: 0.318s

We can also verify all currently deployed changes with the "verify" command:

  > sqitch verify
  Verifying flipr_test
    * appschema .. ok
    * users ...... ok
  Verify successful

Now have a look at the status:

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   d251b2c9b4bc46a4b4db6b7a8a637951484e6f6b
  # Name:     users
  # Deployed: 2018-07-27 11:09:12 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

Success! Let's make sure we can revert the change, as well:

  > sqitch revert --to @HEAD^ -y
  Reverting changes to appschema from flipr_test
    - users .. ok

Note that we've used the "--to" option to specify the change to revert to. And what do we revert to? The symbolic tag @HEAD, when passed to "revert", always refers to the last change deployed to the database. (For other commands, it refers to the last change in the plan.) Appending the caret ("^") tells Sqitch to select the change prior to the last deployed change. So we revert to "appschema", the penultimate change. The other potentially useful symbolic tag is @ROOT, which refers to the first change deployed to the database (or in the plan, depending on the command).

Back to the database. The "users" table should be gone but the "flipr" schema should still be around:

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE TABLES LIKE 'users' IN flipr"
  +------------+------+------+---------------+-------------+
  | created_on | name | kind | database_name | schema_name |
  |------------+------+------+---------------+-------------|
  +------------+------+------+---------------+-------------+
  0 Row(s) produced. Time Elapsed: 0.367s

The "status" command politely informs us that we have undeployed changes:

  # On database flipr_test
  # Project:  flipr
  # Change:   5a2ac4ae6801bfe392483ee5912b4e3592cdd57a
  # Name:     appschema
  # Deployed: 2018-07-27 10:52:54 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Undeployed change:
    * users

As does the "verify" command:

  > sqitch verify
  Verifying flipr_test
    * appschema .. ok
  Undeployed change:
    * users
  Verify successful

Note that the verify is successful, because all currently-deployed changes are verified. The list of undeployed changes (just "users" here) reminds us about the current state.

Okay, let's commit and deploy again:

  > git add .
  > git commit -am 'Add users table.'
  [main 8c16c09] Add users table.
   4 files changed, 22 insertions(+)
   create mode 100644 deploy/users.sql
   create mode 100644 revert/users.sql
   create mode 100644 verify/users.sql
  > sqitch deploy
  Deploying changes to flipr_test
    + users .. ok

Looks good. Check the status:

  > sqitch status
  # Project:  flipr
  # Change:   d251b2c9b4bc46a4b4db6b7a8a637951484e6f6b
  # Name:     users
  # Deployed: 2018-07-27 11:19:30 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

Excellent. Let's do some more!

Add Two at Once

Let's add a couple more changes. Our app will need to store status messages from users. Let's call them -- and the table to store them -- "flips". And we'll also need a view that lists user names with their flips. Let's add changes for them both:

  > sqitch add flips -r appschema -r users -n 'Adds table for storing flips.'
  Created deploy/flips.sql
  Created revert/flips.sql
  Created verify/flips.sql
  Added "flips [appschema users]" to sqitch.plan
  > sqitch add userflips -r appschema -r users -r flips \
    -n 'Creates the userflips view.'
  Created deploy/userflips.sql
  Created revert/userflips.sql
  Created verify/userflips.sql
  Added "userflips [appschema users flips]" to sqitch.plan

Now might be a good time to have a look at the deployment plan:

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/sqitchers/sqitch-snowflake-intro/
  appschema 2018-07-27T14:27:24Z Marge N. OXVera <marge@example.com> # Add schema for all flipr objects.
  users [appschema] 2018-07-27T15:03:56Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
  flips [appschema users] 2018-07-27T15:23:41Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
  userflips [appschema users flips] 2018-07-27T15:23:50Z Marge N. OXVera <marge@example.com> # Creates the userflips view.

Each change appears on a single line with the name of the change, a bracketed list of dependencies, a timestamp, the name and email address of the user who planned the change, and a note.

Let's write the code for the new changes. Here's what deploy/flips.sql should look like:

  -- Deploy flipr:flips to snowflake
  -- requires: appschema
  -- requires: users
  USE WAREHOUSE &warehouse;
  CREATE TABLE flipr.flips (
      id        INTEGER        PRIMARY KEY,
      nickname  TEXT           NOT NULL REFERENCES flipr.users(nickname),
      body      VARCHAR(180)   NOT NULL DEFAULT '',
      timestamp TIMESTAMP_TZ NOT NULL DEFAULT CURRENT_TIMESTAMP
  );

Here's what verify/flips.sql might look like:

  -- Verify flipr:flips on snowflake
  USE WAREHOUSE &warehouse;
  SELECT id, nickname, body, timestamp
    FROM flipr.flips
   WHERE FALSE;

And revert/flips.sql should look something like this:

  -- Revert flipr:flips from snowflake
  USE WAREHOUSE &warehouse;
  DROP TABLE flipr.flips;

Now for "userflips"; deploy/userflips.sql might look like this:

  -- Deploy flipr:userflips to snowflake
  -- requires: appschema
  -- requires: users
  -- requires: flips
  USE WAREHOUSE &warehouse;
  CREATE OR REPLACE VIEW flipr.userflips AS
  SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
    FROM flipr.users u
    JOIN flipr.flips f ON u.nickname = f.nickname;

Use a "SELECT" statement in verify/userflips.sql again:

  -- Verify flipr:userflips on snowflake
  USE WAREHOUSE &warehouse;
  SELECT id, nickname, fullname, body, timestamp
    FROM flipr.userflips
   WHERE FALSE;

And of course, its "revert" script, revert/userflips.sql, should look something like:

  -- Revert flipr:userflips from snowflake
  USE WAREHOUSE &warehouse;
  DROP VIEW flipr.userflips;

Try em out!

  > sqitch deploy
  Deploying changes to flipr_test
    + flips ...... ok
    + userflips .. ok

Do we have the new table and view? Of course we do, they were verified. Still, have a look:

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE TABLES LIKE 'flips' IN flipr"
  +-------------------------------+-------+-------+---------------+-------------+
  | created_on                    | name  | kind  | database_name | schema_name |
  |-------------------------------+-------+-------+---------------+-------------|
  | 2018-07-27 15:31:07.137 +0000 | FLIPS | TABLE | DWHEELER      | FLIPR       |
  +-------------------------------+-------+-------+---------------+-------------+
  1 Row(s) produced. Time Elapsed: 0.225s
  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE VIEWS LIKE 'userflips' IN flipr"
  +-------------------------------+-----------+------+---------------+-------------+
  | created_on                    | name      | kind | database_name | schema_name |
  |-------------------------------+-----------+------+---------------+-------------|
  | 2018-07-27 15:29:25.733 +0000 | USERFLIPS | VIEW | DWHEELER      | FLIPR       |
  +-------------------------------+-----------+------+---------------+-------------+
  1 Row(s) produced. Time Elapsed: 0.299s

And what's the status?

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   73cd50c99de2a8b3eab206c73514afbeb952023c
  # Name:     userflips
  # Deployed: 2018-07-27 11:31:24 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

Looks good. Let's make sure revert works:

  > sqitch revert -y --to @HEAD^^
  Reverting changes to users from flipr_test
    - userflips .. ok
    - flips ...... ok
  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW TERSE TABLES LIKE 'flips' IN flipr"
  +------------+------+------+---------------+-------------+
  | created_on | name | kind | database_name | schema_name |
  |------------+------+------+---------------+-------------|
  +------------+------+------+---------------+-------------+
  0 Row(s) produced. Time Elapsed: 0.306s

Note the use of "@HEAD^^" to specify that the revert be to two changes prior the last deployed change. Looks good. Let's do the commit and re-deploy dance:

  > git add .
  > git commit -m 'Add flips table and userflips view.'
  [main b36f48b] Add flips table and userflips view.
   7 files changed, 43 insertions(+)
   create mode 100644 deploy/flips.sql
   create mode 100644 deploy/userflips.sql
   create mode 100644 revert/flips.sql
   create mode 100644 revert/userflips.sql
   create mode 100644 verify/flips.sql
   create mode 100644 verify/userflips.sql
  > sqitch deploy
  Deploying changes to flipr_test
    + flips ...... ok
    + userflips .. ok
  > sqitch status
  # Project:  flipr
  # Change:   73cd50c99de2a8b3eab206c73514afbeb952023c
  # Name:     userflips
  # Deployed: 2018-07-27 11:38:02 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)
  > sqitch verify
  Verifying flipr_test
    * appschema .. ok
    * users ...... ok
    * flips ...... ok
    * userflips .. ok
  Verify successful

Great, we're fully up-to-date!

Ship It!

Let's do a first release of our app. Let's call it "1.0.0-dev1" Since we want to have it go out with deployments tied to the release, let's tag it:

  > sqitch tag v1.0.0-dev1 -n 'Tag v1.0.0-dev1.'
  Tagged "userflips" with @v1.0.0-dev1
  > git commit -am 'Tag the database with v1.0.0-dev1.'
  [main 84ed9db] Tag the database with v1.0.0-dev1.
   1 files changed, 1 insertion(+)
  > git tag v1.0.0-dev1 -am 'Tag v1.0.0-dev1'

We can try deploying to make sure the tag gets picked up like so:

  > sqitch deploy
  Nothing to deploy (up-to-date)
  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   73cd50c99de2a8b3eab206c73514afbeb952023c
  # Name:     userflips
  # Tag:      @v1.0.0-dev1
  # Deployed: 2018-07-27 11:38:02 -0400
  # By:       Marge N. OXVera <marge@example.com>
  #
  Nothing to deploy (up-to-date)

Note the new "Tag" line in the output of "sqitch status": no new changes needed to be deployed, but Sqitch did deploy the tag on the "userflips" change. Now let's bundle everything up for release:

  > sqitch bundle
  Bundling into bundle
  Writing config
  Writing plan
  Writing scripts
    + appschema
    + users
    + flips
    + userflips @v1.0.0-dev1

Now we can package the bundle directory and distribute it. When it gets installed somewhere, users can use Sqitch to deploy to the database. Let's try deploying it to another database, "flipr_prod":

  > cd bundle
  > sqitch deploy 'db:snowflake://movera@example/flipr_prod?Driver=Snowflake'
  Adding registry tables to db:snowflake://movera@example/flipr_prod?Driver=Snowflake'
  Deploying changes to db:snowflake://movera@example/flipr_prod?Driver=Snowflake'
    + appschema ............... ok
    + users ................... ok
    + flips ................... ok
    + userflips @v1.0.0-dev1 .. ok

Notice how the tag on "userflips" now appears in the deploy output. Nice, eh? Now, package it up and ship it!

  > cd ..
  > mv bundle flipr-v1.0.0-dev1
  > tar -czf flipr-v1.0.0-dev1.tgz flipr-v1.0.0-dev1

Making a Hash of Things

Now that we've got the basics of the app done, let's add a feature. Gotta track the hashtags associated with flips, right? Let's add a table for them. But since other folks are working on other tasks in the repository, we'll work on a branch, so we can all stay out of each other's way. So let's branch:

  > git checkout -b hashtags
  Switched to a new branch 'hashtags'

Now we can add a new change to create a table for hashtags.

  > sqitch add hashtags --requires flips -n 'Adds table for storing hashtags.'
  Created deploy/hashtags.sql
  Created revert/hashtags.sql
  Created verify/hashtags.sql
  Added "hashtags [appschema flips]" to sqitch.plan

You know the drill by now. Add this to deploy/hashtags.sql

  CREATE TABLE flipr.hashtags (
      flip_id   INTEGER       NOT NULL REFERENCES flipr.flips(id),
      hashtag   VARCHAR(128)  NOT NULL,
      PRIMARY KEY (flip_id, hashtag)
  );

Again, select from the table in verify/hashtags.sql:

  SELECT flip_id, hashtag FROM flipr.hashtags WHERE FALSE;

And drop it in revert/hashtags.sql

  DROP TABLE flipr.hashtags;

And give it a whirl:

  > sqitch deploy
  Deploying changes to flipr_test
    + hashtags .. ok

Look good?

  > sqitch status --show-tags
  # On database flipr_test
  # Project:  flipr
  # Change:   d750cbeec487841c45715115a31297739fbb4046
  # Name:     hashtags
  # Deployed: 2018-07-27 11:53:02 -0400
  # By:       Marge N. OXVera <marge@example.com>
  # 
  # Tag:
  #   @v1.0.0-dev1 - 2018-07-27 11:41:13 -0400 - Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Note the use of "--show-tags" to show all the deployed tags. Make sure we can revert, too:

  > sqitch revert -y --onto @HEAD^
  Reverting changes to userflips @v1.0.0-dev1 from flipr_test
    - hashtags .. ok
  > sqitch deploy
  Deploying changes to flipr_test
    + hashtags .. ok

Great! Now make it so:

  > git add .
  > git commit -m 'Add hashtags table.'
  [hashtags 06a0bf4] Add hashtags table.
   4 files changed, 19 insertions(+)
   create mode 100644 deploy/hashtags.sql
   create mode 100644 revert/hashtags.sql
   create mode 100644 verify/hashtags.sql

Good, we've finished this feature. Time to merge back into "main".

  > git checkout main
  Switched to branch 'main'
  > git pull
  Updating 84ed9db..31d026c
  Fast-forward
   deploy/lists.sql | 11 +++++++++++
   revert/lists.sql |  4 ++++
   sqitch.plan      |  2 ++
   verify/lists.sql |  6 ++++++
   4 files changed, 23 insertions(+)
   create mode 100644 deploy/lists.sql
   create mode 100644 revert/lists.sql
   create mode 100644 verify/lists.sql

  > git merge --no-ff hashtags
  Auto-merging sqitch.plan
  CONFLICT (content): Merge conflict in sqitch.plan
  Automatic merge failed; fix conflicts and then commit the result.

  > git reset --hard HEAD
  HEAD is now at 31d026c Merge branch 'lists'

  > git checkout hashtags
  Switched to branch 'hashtags'
  > git rebase main
  First, rewinding head to replay your work on top of it...
  Applying: Add hashtags table.
  Using index info to reconstruct a base tree...
  M     sqitch.plan
  Falling back to patching base and 3-way merge...
  Auto-merging sqitch.plan
  CONFLICT (content): Merge conflict in sqitch.plan
  error: Failed to merge in the changes.
  Patch failed at 0001 Add hashtags table.
  Use 'git am --show-current-patch' to see the failed patch
  Resolve all conflicts manually, mark them as resolved with
  "git add/rm <conflicted_files>", then run "git rebase --continue".
  You can instead skip this commit: run "git rebase --skip".
  To abort and get back to the state before "git rebase", run "git rebase --abort".

  > git rebase --abort
  HEAD is now at 06a0bf4 Add hashtags table.

  > echo sqitch.plan merge=union > .gitattributes
  > git rebase main
  First, rewinding head to replay your work on top of it...
  Applying: Add hashtags table.
  Using index info to reconstruct a base tree...
  M     sqitch.plan
  Falling back to patching base and 3-way merge...
  Auto-merging sqitch.plan

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/sqitchers/sqitch-snowflake-intro/
  appschema 2018-07-27T14:27:24Z Marge N. OXVera <marge@example.com> # Add schema for all flipr objects.
  users [appschema] 2018-07-27T15:03:56Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
  flips [appschema users] 2018-07-27T15:23:41Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
  userflips [appschema users flips] 2018-07-27T15:23:50Z Marge N. OXVera <marge@example.com> # Creates the userflips view.
  @v1.0.0-dev1 2018-07-27T15:40:25Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.
  lists [appschema flips] 2018-07-27T16:00:00Z Marge N. OXVera <marge@example.com> # Adds table for storing lists.
  hashtags [flips] 2018-07-27T15:51:16Z Marge N. OXVera <marge@example.com> # Adds table for storing hashtags.

  > sqitch rebase -y
  Reverting all changes from flipr_test
    - hashtags ................ ok
    - userflips @v1.0.0-dev1 .. ok
    - flips ................... ok
    - users ................... ok
    - appschema ............... ok
  Deploying changes to flipr_test
    + appschema ............... ok
    + users ................... ok
    + flips ................... ok
    + userflips @v1.0.0-dev1 .. ok
    + lists ................... ok
    + hashtags ................ ok

  > git add .
  > git commit -m 'Add `.gitattributes` with union merge for `sqitch.plan`.'
  [hashtags 86596a9] Add `.gitattributes` with union merge for `sqitch.plan`.
   1 files changed, 1 insertions(+), 0 deletions(-)
   create mode 100644 .gitattributes

  > git checkout main
  Switched to branch 'main'
  > git merge --no-ff hashtags -m "Merge branch 'hashtags'"
  Merge made by the 'recursive' strategy.
   .gitattributes      | 1 +
   deploy/hashtags.sql | 9 ++++++++++
   revert/hashtags.sql | 4 ++++
   sqitch.plan         | 1 +
   verify/hashtags.sql | 4 ++++
   5 files changed, 19 insertions(+)
   create mode 100644 .gitattributes
   create mode 100644 deploy/hashtags.sql
   create mode 100644 revert/hashtags.sql
   create mode 100644 verify/hashtags.sql

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/sqitchers/sqitch-snowflake-intro/
  appschema 2018-07-27T14:27:24Z Marge N. OXVera <marge@example.com> # Add schema for all flipr objects.
  users [appschema] 2018-07-27T15:03:56Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
  flips [appschema users] 2018-07-27T15:23:41Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
  userflips [appschema users flips] 2018-07-27T15:23:50Z Marge N. OXVera <marge@example.com> # Creates the userflips view.
  @v1.0.0-dev1 2018-07-27T15:40:25Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.
  lists [appschema flips] 2018-07-27T16:00:00Z Marge N. OXVera <marge@example.com> # Adds table for storing lists.
  hashtags [flips] 2018-07-27T15:51:16Z Marge N. OXVera <marge@example.com> # Adds table for storing hashtags.

  > sqitch tag v1.0.0-dev2 -n 'Tag v1.0.0-dev2.'
  Tagged "hashtags" with @v1.0.0-dev2
  > git commit -am 'Tag the database with v1.0.0-dev2.'
  [main 1c67e0d] Tag the database with v1.0.0-dev2.
   1 files changed, 1 insertion(+)
  > git tag v1.0.0-dev2 -am 'Tag v1.0.0-dev2'
  > sqitch bundle --dest-dir flipr-1.0.0-dev2
  Bundling into flipr-1.0.0-dev2
  Writing config
  Writing plan
  Writing scripts
    + appschema
    + users
    + flips
    + userflips @v1.0.0-dev1
    + lists
    + hashtags @v1.0.0-dev2

In Place Changes

Well, some folks have been testing the "1.0.0-dev2" release and have demanded that Twitter user links be added to Flipr pages. Why anyone would want to include social network links in an anti-social networking app is beyond us programmers, but we're just the plumbers, right? Gotta go with what Product demands. The upshot is that we need to update the "userflips" view, which is used for the feature in question, to include the Twitter user names.

Normally, modifying views in database changes is a PITA <https://www.urbandictionary.com/define.php?term=pita>. You have to make changes like these:

1.

Copy deploy/userflips.sql to deploy/userflips_twitter.sql.

2.

Edit deploy/userflips_twitter.sql to drop and re-create the view with the "twitter" column to the view.

3.

Copy deploy/userflips.sql to revert/userflips_twitter.sql. Yes, copy the original change script to the new revert change.

4.

Add a "DROP VIEW" statement to revert/userflips_twitter.sql.

5.

Copy verify/userflips.sql to verify/userflips_twitter.sql.

6.

Modify verify/userflips_twitter.sql to include a check for the "twiter" column.

7.

Test the changes to make sure you can deploy and revert the "userflips_twitter" change.

But you can have Sqitch do most of the work for you. The only requirement is that a tag appear between the two instances of a change we want to modify. In general, you're going to make a change like this after a release, which you've tagged anyway, right? Well we have, with "@v1.0.0-dev2" added in the previous section. With that, we can let Sqitch do most of the hard work for us, thanks to the "rework" command, which is similar to "add":

  > sqitch rework userflips -n 'Adds userflips.twitter.'
  Added "userflips [userflips@v1.0.0-dev2]" to sqitch.plan.
  Modify these files as appropriate:
    * deploy/userflips.sql
    * revert/userflips.sql
    * verify/userflips.sql

Oh, so we can edit those files in place. Nice! How does Sqitch do it? Well, in point of fact, it has copied the files to stand in for the previous instance of the "userflips" change, which we can see via "git status":

  > git status
  On branch main
  Your branch is up to date with 'origin/main'.
  Changes not staged for commit:
    (use "git add <file>..." to update what will be committed)
    (use "git checkout -- <file>..." to discard changes in working directory)
    modified:   revert/userflips.sql
    modified:   sqitch.plan
  Untracked files:
    (use "git add <file>..." to include in what will be committed)
    deploy/userflips@v1.0.0-dev2.sql
    revert/userflips@v1.0.0-dev2.sql
    verify/userflips@v1.0.0-dev2.sql
  no changes added to commit (use "git add" and/or "git commit -a")

The "Untracked files" part of the output is the first thing to notice. They're all named "userflips@v1.0.0-dev2.sql". What that means is: "the "userflips" change as it was implemented as of the "@v1.0.0-dev2" tag." These are copies of the original scripts, and thereafter Sqitch will find them when it needs to run scripts for the first instance of the "userflips" change. As such, it's important not to change them again. But hey, if you're reworking the change, you shouldn't need to.

The other thing to notice is that revert/userflips.sql has changed. Sqitch replaced it with the original deploy script. As of now, deploy/userflips.sql and revert/userflips.sql are identical. This is on the assumption that the deploy script will be changed (we're reworking it, remember?), and that the revert script should actually change things back to how they were before. Of course, the original deploy script may not be idempotent <https://en.wikipedia.org/wiki/Idempotence> -- that is, able to be applied multiple times without changing the result beyond the initial application. If it's not, you will likely need to modify it so that it properly restores things to how they were after the original deploy script was deployed. Or, more simply, it should revert changes back to how they were as-of the deployment of deploy/userflips@v1.0.0-dev2.sql.

Fortunately, our view deploy scripts are already idempotent, thanks to the use of the "OR REPLACE" expression. No matter how many times a deployment script is run, the end result will be the same instance of the view, with no duplicates or errors.

As a result, there is no need to explicitly add changes. So go ahead. Modify the script to add the "twitter" column to the view. Make this change to deploy/userflips.sql:

  @@ -5,6 +5,6 @@
  
  USE WAREHOUSE &warehouse;
  CREATE OR REPLACE VIEW flipr.userflips AS
  -SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
  +SELECT SELECT f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp
    FROM flipr.users u
    JOIN flipr.flips f ON u.nickname = f.nickname;

Next, modify verify/userflips.sql to check for the "twitter" column. Here's the diff:

  @@ -1,6 +1,6 @@
   -- Verify flipr:userflips on snowflake
  -SELECT id, nickname, fullname, body, timestamp
  +SELECT id, nickname, fullname, twitter, body, timestamp
     FROM flipr.userflips
    WHERE FALSE;

Now try a deployment:

  > sqitch deploy
  Deploying changes to flipr_test
    + userflips .. ok

So, are the changes deployed?

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW VIEWS LIKE 'userflips' IN flipr"
  +-------------------------------+-----------+----------+---------------+-------------+--------+---------+---------------------------------------------------------------------+-----------+
  | created_on                    | name      | reserved | database_name | schema_name | owner  | comment | text                                                                | is_secure |
  |-------------------------------+-----------+----------+---------------+-------------+--------+---------+---------------------------------------------------------------------+-----------|
  | 2018-07-27 18:19:29.818 +0000 | USERFLIPS |          | DWHEELER      | FLIPR       | SQITCH |         | CREATE OR REPLACE VIEW flipr.userflips AS                           | false     |
  |                               |           |          |               |             |        |         | SELECT f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp |           |
  |                               |           |          |               |             |        |         |   FROM flipr.users u                                                |           |
  |                               |           |          |               |             |        |         |   JOIN flipr.flips f ON u.nickname = f.nickname;                    |           |
  +-------------------------------+-----------+----------+---------------+-------------+--------+---------+---------------------------------------------------------------------+-----------+
  1 Row(s) produced. Time Elapsed: 0.413s

Awesome, the view now includes the "twitter" column. But can we revert?

  > sqitch revert --to @HEAD^ -y
  Reverting changes to hashtags @v1.0.0-dev2 from flipr_test
    - userflips .. ok

Did that work, is the "twitter" column gone?

  > snowsql --accountname example --username movera --dbname flipr -o friendly=false \
    --query "SHOW VIEWS LIKE 'userflips' IN flipr"
  +-------------------------------+-----------+----------+---------------+-------------+--------+---------+----------------------------------------------------------+-----------+
  | created_on                    | name      | reserved | database_name | schema_name | owner  | comment | text                                                     | is_secure |
  |-------------------------------+-----------+----------+---------------+-------------+--------+---------+----------------------------------------------------------+-----------|
  | 2018-07-27 18:50:52.064 +0000 | USERFLIPS |          | DWHEELER      | FLIPR       | SQITCH |         | CREATE OR REPLACE VIEW flipr.userflips AS                | false     |
  |                               |           |          |               |             |        |         | SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp |           |
  |                               |           |          |               |             |        |         |   FROM flipr.users u                                     |           |
  |                               |           |          |               |             |        |         |   JOIN flipr.flips f ON u.nickname = f.nickname;         |           |
  +-------------------------------+-----------+----------+---------------+-------------+--------+---------+----------------------------------------------------------+-----------+
  1 Row(s) produced. Time Elapsed: 0.362s

Yes, it works! Sqitch properly finds the original instances of these changes in the new script files that include tags.

Excellent. Let's go ahead and commit these changes:

  > git add .
  > git commit -m 'Add the twitter column to the userflips view.'
  [main c004445] Add the twitter column to the userflips view.
   7 files changed, 31 insertions(+), 4 deletions(-)
   create mode 100644 deploy/userflips@v1.0.0-dev2.sql
   create mode 100644 revert/userflips@v1.0.0-dev2.sql
   create mode 100644 verify/userflips@v1.0.0-dev2.sql

More to Come

Sqitch is a work in progress. Better integration with version control systems is planned to make managing idempotent reworkings even easier. Stay tuned.

Author

David E. Wheeler <david@justatheory.com>

License

Copyright (c) 2012-2022 iovation Inc., David E. Wheeler

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.