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sqitchtutorial-sqlite(User Contributed Perl Documentatsqitchtutorial-sqlite(3)

Name
       sqitchtutorial-sqlite - A tutorial introduction to Sqitch change
       management on SQLite

Synopsis
	 sqitch	*

Description
       This tutorial explains how to create a sqitch-enabled SQLite 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 new project from	scratch, a fictional
       antisocial networking site called Flipr.	All examples use Git
       <http://git-scm.com/> as	the VCS	and SQLite <http://www.sqlite.org/> as
       the storage engine.

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

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

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

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

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

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 -m 'Initialize project, add README.'
	 [master (root-commit) 253542e]	Initialize project, add	README.
	  1 file changed, 37 insertions(+)
	  create mode 100644 README.md

       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/theory/sqitch-sqlite-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, so let's specify one when
       we initialize Sqitch:

	 > sqitch init flipr --uri https://github.com/theory/sqitch-sqlite-intro/ --engine sqlite
	 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 =	sqlite
	       # plan_file = sqitch.plan
	       # top_dir = .
	 # [engine "sqlite"]
	       # target	= db:sqlite:
	       # registry = sqitch
	       # client	= sqlite3

       Good, it	picked up on the fact that we're creating changes for the
       SQLite engine, thanks to	the "-engine sqlite" option, and saved it to
       the file.  Furthermore, it wrote	a commented-out	"[engine "sqlite"]"
       section with all	the available SQLite 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 SQLite's	"sqlite3" client is not	in the path on my
       system, let's go	ahead an tell it where to find the client on our
       computer.

	 > sqitch config --user	engine.sqlite.client /opt/local/bin/sqlite3

       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 "sqlite"]
	       client =	/opt/local/bin/sqlite3
	 [user]
	       name = Marge N. OXVera
	       email = marge@example.com

       Which means that	Sqitch should be able to find "sqlite3"	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/theory/sqitch-sqlite-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 -m 'Initialize Sqitch configuration.'
	 [master 91e2f0d] Initialize Sqitch configuration.
	  2 files changed, 19 insertions(+)
	  create mode 100644 sqitch.conf
	  create mode 100644 sqitch.plan

Our First Change
       Let's create a table. Our app will need users, of course, so we'll
       create a	table for them.	Run this command:

	 > sqitch add users -n 'Creates	table to track our users.'
	 Created deploy/users.sql
	 Created revert/users.sql
	 Created verify/users.sql
	 Added "users" 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 table.	By default,
       the deploy/users.sql file looks like this:

	 -- Deploy flipr:users to sqlite

	 BEGIN;

	 -- XXX	Add DDLs here.

	 COMMIT;

       What we want to do is to	replace	the "XXX" comment with the "CREATE
       TABLE" statement, like so:

	 -- Deploy flipr:users to sqlite

	 BEGIN;

	 CREATE	TABLE users (
		 nickname  TEXT	     PRIMARY KEY,
		 password  TEXT	     NOT NULL,
		 fullname  TEXT	     NOT NULL,
		 twitter   TEXT	     NOT NULL,
		 timestamp DATETIME  NOT NULL DEFAULT CURRENT_TIMESTAMP
	 );

	 COMMIT;

       The "revert" script's job is to precisely revert	the change to the
       deploy script, so we edit this to revert/users.sql to look like this:

	 -- Revert flipr:users from sqlite

	 BEGIN;

	 DROP TABLE users;

	 COMMIT;

       Now we can try deploying	this change:

	 > sqitch deploy db:sqlite:flipr_test.db
	 Adding	registry tables	to db:sqlite:sqitch.db
	 Deploying changes to db:sqlite:flipr_test.db
	   + users .. ok

       First Sqitch created the	registry database and tables used to track
       database	changes. The registry is separate from the database to which
       the "users" change was deployed;	by default, its	name is
       "sqitch.$suffix", where $suffix is the same as the suffix on the	target
       database, if any. It lives in the same directory	as the target
       database. This will be useful if	you use	the SQLite "ATTACHDATABASE"
       <http://www.sqlite.org/lang_attach.html>	command	to manage multiple
       database	files in a single project. In that case, you will want to use
       the same	file for all the databases. Keep them all in the same
       directory with the same suffix and you get just that with the default
       sqitch database.

       If you'd	like it	to have	a different name for the registry database,
       use "sqitch engine add sqlite $name" to configure it (or	via the
       "target"	command; more below). This will	be useful if you don't want to
       use the same registry database to manage	multiple databases, or if you
       do, but they live in different directories.

       Next, Sqitch deploys changes to the target database, which we specified
       on the command-line. We only have one so	far; the "+" reinforces	the
       idea that the change is being added to the database.

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

	       > sqlite3 flipr_test.db '.tables'
	       users

   Trust, But Verify
       But that's too much work. do you	really want to do something like that
       after every deploy?

       Here's where the	"verify" script	comes in. Its job is to	test that the
       deploy did was it was supposed to. It should do so without regard to
       any data	that might be in the database, and should throw	an error if
       the deploy was not successful. The easiest way to do that with a	table
       is to simply "SELECT" from it. Put this query into verify/users.sql:

	 SELECT	nickname, password, fullname, twitter
	       FROM users
	  WHERE	0;

       Now you can run the "verify" script with	the "verify" command:

	 > sqitch verify db:sqlite:flipr_test.db
	 Verifying db:sqlite:flipr_test.db
	       * users .. ok
	 Verify	successful

       Looks good! If you want to make sure that the verify script correctly
       dies if the table doesn't exist,	temporarily change the table name in
       the script to something that doesn't exist, something like:

	 SELECT	nickname, password, timestamp
	       FROM users_nonesuch
	  WHERE	0;

       Then "verify" again:

	 > sqitch verify db:sqlite:flipr_test.db
	 Verifying db:sqlite:flipr_test.db
	   * users .. Error: near line 5: no such table: users_nonesuch
	 # Verify script "verify/users.sql" failed.
	 not ok

	 Verify	Summary	Report
	 ---------------------
	 Changes: 1
	 Errors:  1
	 Verify	failed

       SQLite is kind enough to	tell us	what the problem is. Don't forget to
       change the table	name back before continuing!

   Status, Revert, Log,	Repeat
       For purely informational	purposes, we can always	see how	a deployment
       was recorded via	the "status" command, which reads the tables from the
       registry	database:

	 > sqitch status db:sqlite:flipr_test.db
	 # On database db:sqlite:flipr_test.db
	 # Project:  flipr
	 # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
	 # Name:     users
	 # Deployed: 2013-12-31	10:26:59 -0800
	 # By:	     Marge N. OXVera <marge@example.com>
	 #
	 Nothing to deploy (up-to-date)

       Let's make sure that we can revert the change:

	 > sqitch  revert db:sqlite:flipr_test.db
	 Revert	all changes from db:sqlite:flipr_test.db? [Yes]
	       - users .. ok

       The "revert" command first prompts to make sure that we really do want
       to revert. This is to prevent unnecessary accidents. You	can pass the
       "-y" option to disable the prompt. Also,	notice the "-" before the
       change name in the output, which	reinforces that	the change is being
       removed from the	database. And now the schema should be gone:

	       > sqlite3 flipr_test.db '.tables'

       And the status message should reflect as	much:

	 > sqitch status db:sqlite:flipr_test.db
	 # On database db:sqlite:flipr_test.db
	 No changes deployed

       Of course, since	nothing	is deployed, the "verify" command has nothing
       to verify:

	 > sqitch verify db:sqlite:flipr_test.db
	 Verifying db:sqlite:flipr_test.db
	 No changes deployed

       However,	we still have a	record that the	change happened, visible via
       the "log" command:

	 > sqitch log db:sqlite:flipr_test.db
	 On database db:sqlite:flipr_test.db
	 Revert	f30fe47f5f99501fb8d481e910d9112c5ac0a676
	 Name:	    users
	 Committer: Marge N. OXVera <marge@example.com>
	 Date:	    2013-12-31 10:53:25	-0800

	     Creates table to track our	users.

	 Deploy	f30fe47f5f99501fb8d481e910d9112c5ac0a676
	 Name:	    users
	 Committer: Marge N. OXVera <marge@example.com>
	 Date:	    2013-12-31 10:26:59	-0800

	     Creates table to track our	users.

       Note that the actions we	took are shown in reverse chronological	order,
       with the	revert first and then the deploy.

       Cool. Let's tell	Git to ignore *.db files and then commit it.

	 > echo	'*.db' > .gitignore
	 > git add .
	 > git commit -m 'Add users table.'
	 [master 6725454] Add users table.
	  5 files changed, 31 insertions(+)
	  create mode 100644 .gitignore
	  create mode 100644 deploy/users.sql
	  create mode 100644 revert/users.sql
	  create mode 100644 verify/users.sql

       And then	deploy again. This time, let's use the "--verify" option, so
       that the	"verify" script	is applied when	the change is deployed:

	 > sqitch deploy db:sqlite:flipr_test.db --verify
	 Deploying changes to db:sqlite:flipr_test.db
	       + users .. ok

       And now the "users" table should	be back:

	 > sqlite3 flipr_test.db '.tables'
	 users

       When we look at the status, the deployment will be there:

	 > sqitch status db:sqlite:flipr_test.db
	 # On database db:sqlite:flipr_test.db
	 # Project:  flipr
	 # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
	 # Name:     users
	 # Deployed: 2013-12-31	10:57:55 -0800
	 # 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:sqlite:flipr_test.db", aren't you? This database connection URI
       <https://github.com/theory/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:sqlite:flipr_test.db

       The "target" command, inspired by "git-remote" <http://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 sqlite 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:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
	 # Name:     users
	 # Deployed: 2013-12-31	10:57:55 -0800
	 # 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 target and always verify.'
	 [master 5fb57ec] Set default target and always	verify.
	  1 file changed, 8 insertions(+)

Deploy with Dependency
       Let's add another change. Our app will need to store status messages
       from users. Let's call them -- and the table to store them -- "flips".
       First, add the new change:

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

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

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

	 -- Deploy flipr:flips to sqlite
	 -- requires: users

	 BEGIN;

	 CREATE	TABLE flips (
		 id	   INTEGER   PRIMARY KEY AUTOINCREMENT,
		 nickname  TEXT	     NOT NULL REFERENCES users(nickname),
		 body	   TEXT	     NOT NULL DEFAULT '' CHECK ( length(body) <= 180 ),
		 timestamp DATETIME  NOT NULL DEFAULT CURRENT_TIMESTAMP
	 );

	 COMMIT;

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

       The "users.nickname" column references the "users" table. This is why
       we need to require the "users" change.

       Now for the verify script. Again, all we	need to	do is "SELECT" from
       the table. I recommend selecting	each column by name, too, to be	sure
       that no column is missing. Here's the verify/flips.sql:

	 -- Verify flipr:flips on sqlite

	 BEGIN;

	 SELECT	id, nickname, body, timestamp
	       FROM flips
	  WHERE	0;

	 COMMIT;

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

	 -- Revert flipr:flips from sqlite

	 BEGIN;

	 DROP TABLE flips;

	 COMMIT;

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

	 > sqitch deploy
	 Deploying changes to flipr_test
	       + flips .. 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:

	 > sqlite3 flipr_test.db '.tables'
	 flips	users

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

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

       Now have	a look at the status:

	 > sqitch status
	 # On database flipr_test
	 # Project:  flipr
	 # Change:   32ee57069c0d7fec52b6f86f453dc0c16bc1090a
	 # Name:     flips
	 # Deployed: 2013-12-31	11:02:51 -0800
	 # 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 users from flipr_test
	   - flips .. 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 "users", 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 "flips" table should be gone but the "users"
       table should still be around:

	 > sqlite3 flipr_test.db '.tables'
	 users

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

	 > sqitch status
	 # On database flipr_test
	 # Project:  flipr
	 # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
	 # Name:     users
	 # Deployed: 2013-12-31	10:57:55 -0800
	 # By:	     Marge N. OXVera <marge@example.com>
	 #
	 Undeployed change:
	   * flips

       As does the "verify" command:

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

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

       Okay, let's commit and deploy again:

	 > git add .
	 > git commit -am 'Add flips table.'
	 [master 21cba95] Add flips table.
	  4 files changed, 30 insertions(+)
	  create mode 100644 deploy/flips.sql
	  create mode 100644 revert/flips.sql
	  create mode 100644 verify/flips.sql
	 > sqitch deploy
	 Deploying changes to flipr_test
	   + flips .. ok

       Looks good. Check the status:

	 > sqitch status
	 # On database flipr_test
	 # Project:  flipr
	 # Change:   32ee57069c0d7fec52b6f86f453dc0c16bc1090a
	 # Name:     flips
	 # Deployed: 2013-12-31	11:05:44 -0800
	 # By:	     Marge N. OXVera <marge@example.com>
	 #
	 Nothing to deploy (up-to-date)

View to	a Thrill
       One more	thing to add before we are ready to ship a first beta release.
       Let's create a view that	lists user names with their flips.

	 > sqitch add userflips	--requires users --requires flips \
	       -n 'Creates the userflips view.'
	 Created deploy/userflips.sql
	 Created revert/userflips.sql
	 Created verify/userflips.sql
	 Added "userflips [users flips]" to sqitch.plan

       Now add this SQL	to deploy/userflips.sql:

	 CREATE	VIEW userflips AS
	 SELECT	f.id, u.nickname, u.fullname, f.body, f.timestamp
	       FROM users u
	       JOIN flips f ON u.nickname = f.nickname;

       Add this	SQL to verify/userflips.sql

	 SELECT	id, nickname, fullname,	body, timestamp
	       FROM userflips
	  WHERE	0;

       And add the "DROP VIEW" statement to revert/userflips.sql:

	 DROP VIEW userflips;

       Now Try it out!

	 > sqitch deploy
	 Deploying changes to flipr_test
	   + userflips .. ok
	 > sqitch revert -y
	 Reverting all changes from flipr_test
	   - userflips .. ok
	   - flips ...... ok
	   - users ...... ok
	 > sqitch deploy
	 Deploying changes to flipr_test
	   + users ...... ok
	   + flips ...... ok
	   + userflips .. ok

       Looks good! Commit it.

	 > git add .
	 > git commit -m 'Add the userflips view.'
	 [master c74bfb4] Add the userflips view.
	  4 files changed, 29 insertions(+)
	  create mode 100644 deploy/userflips.sql
	  create mode 100644 revert/userflips.sql
	  create mode 100644 verify/userflips.sql

Ship It!
       Now we're ready for the first development 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.'
	 [master 7a479fd] Tag the database with	v1.0.0-dev1.
	  1 file 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:

	 > mkdir dev
	 > sqitch deploy db:sqlite:dev/flipr.db
	 Adding	registry tables	to db:sqlite:dev/sqitch.db
	 Deploying changes to db:sqlite:dev/flipr.db
	   + users ................... ok
	   + flips ................... ok

       Great, both changes were	deployed and "userflips" was tagged with
       "@v1.0.0-dev1". Let's have a look at the	status:

	 > sqitch status db:sqlite:dev/flipr_dev.db
	 # On database db:sqlite:dev/flipr_dev.db
	 # Project:  flipr
	 # Change:   60ee3aba0445bf3287f9dc1dd97b1877523fa139
	 # Name:     userflips
	 # Tag:	     @v1.0.0-dev1
	 # Deployed: 2013-12-31	11:19:15 -0800
	 # By:	     Marge N. OXVera <marge@example.com>
	 #
	 Nothing to deploy (up-to-date)

       Note the	listing	of the tag as part of the status message. Now let's
       bundle everything up for	release:

	 > rm -rf dev
	 > sqitch bundle
	 Bundling into bundle
	 Writing config
	 Writing plan
	 Writing scripts
	       + 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:

	 > cd bundle
	 > sqitch deploy db:sqlite:flipr_prod.db
	 Adding	registry tables	to db:sqlite:sqitch.db
	 Deploying changes to db:sqlite:flipr_prod.db
	   + users ................... ok
	   + flips ................... ok
	   + userflips @v1.0.0-dev1 .. ok

       Looks much the same as before, eh? Package it up	and ship it!

	 > rm *.db
	 > 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 [flips]" to sqitch.plan

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

	 CREATE	TABLE hashtags (
		 flip_id   INTEGER   NOT NULL REFERENCES flips(id),
		 hashtag   TEXT	     NOT NULL CHECK ( length(hashtag) >	0 ),
		 PRIMARY KEY (flip_id, hashtag)
	 );

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

	 SELECT	flip_id, hashtag FROM hashtags WHERE 0;

       And drop	it in revert/hashtags.sql

	 DROP TABLE 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:   1352464e8b5f3d5eeac76a1986379f07de43bffd
	 # Name:     hashtags
	 # Deployed: 2013-12-31	11:30:53 -0800
	 # By:	     Marge N. OXVera <marge@example.com>
	 #
	 # Tag:
	 #   @v1.0.0-dev1 - 2013-12-31 11:13:49	-0800 -	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 --to @HEAD^ -y
	 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 94f02b8] Add	hashtags table.
	  4 files changed, 28 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 "master".

   Emergency
       Let's do	it:

	 > git checkout	master
	 Switched to branch 'master'
	 > git pull
	 Updating 7a479fd..47a4107
	 Fast-forward
	  deploy/lists.sql | 13	+++++++++++++
	  revert/lists.sql |  7	+++++++
	  sqitch.plan	   |  2	++
	  verify/lists.sql |  9	+++++++++
	  4 files changed, 31 insertions(+)
	  create mode 100644 deploy/lists.sql
	  create mode 100644 revert/lists.sql
	  create mode 100644 verify/lists.sql

       Hrm, that's interesting.	Looks like someone made	some changes to
       "master".  They added list support. Well, let's see what	happens	when
       we merge	our changes.

	 > 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.

       Oh, a conflict in sqitch.plan. Not too surprising, since	both the
       merged "lists" branch and our "hashtags"	branch added changes to	the
       plan. Let's try a different approach.

       The truth is, we	got lazy. Those	changes	when we	pulled master from the
       origin should have raised a red flag. It's considered a bad practice
       not to look at what's changed in	"master" before	merging	in a branch.
       What one	should do is either:

       o   Rebase the hashtags branch from master before merging. This
	   "rewinds" the branch	changes, pulls from "master", and then replays
	   the changes back on top of the pulled changes.

       o   Create a patch and apply that to master. This is the	sort of	thing
	   you might have to do	if you're sending changes to another user,
	   especially if the VCS is not	Git.

       So let's	restore	things to how they were	at master:

	 > git reset --hard HEAD
	 HEAD is now at	47a4107	Merge branch 'lists'

       That throws out our botched merge. Now let's go back to our branch and
       rebase it on "master":

	 > git checkout	hashtags
	 Switched to branch 'hashtags'
	 > git rebase master
	 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
	 Failed	to merge in the	changes.
	 Patch failed at 0001 Add hashtags table.
	 The copy of the patch that failed is found in:
	    .git/rebase-apply/patch

	 When you have resolved	this problem, run "git rebase --continue".
	 If you	prefer to skip this patch, run "git rebase --skip" instead.
	 To check out the original branch and stop rebasing, run "git rebase --abort".

       Oy, that's kind of a pain. It seems like	no matter what we do, we'll
       need to resolve conflicts in that file. Except in Git. Fortunately for
       us, we can tell Git to resolve conflicts	in sqitch.plan differently.
       Because we only ever append lines to the	file, we can have it use the
       "union" merge driver, which, according to its docs <http://git-
       scm.com/docs/gitattributes#_built-in_merge_drivers>:

	   Run 3-way file level	merge for text files, but take lines from both
	   versions, instead of	leaving	conflict markers. This tends to	leave
	   the added lines in the resulting file in random order and the user
	   should verify the result. Do	not use	this if	you do not understand
	   the implications.

       This has	the effect of appending	lines from all the merging files,
       which is	exactly	what we	need. So let's give it a try. First, back out
       the botched rebase:

	 > git rebase --abort

       Now add the union merge driver to .gitattributes	for sqitch.plan	and
       rebase again:

	 > echo	sqitch.plan merge=union	> .gitattributes
	 > git rebase master
	 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

       Ah, that	looks a	bit better. Let's have a look at the plan:

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

	 users 2013-12-31T18:06:04Z Marge N. OXVera <marge@example.com>	# Creates table	to track our users.
	 flips [users] 2013-12-31T19:01:40Z Marge N. OXVera <marge@example.com>	# Adds table for storing flips.
	 userflips [users flips] 2013-12-31T19:11:11Z Marge N. OXVera <marge@example.com> # Creates the	userflips view.
	 @v1.0.0-dev1 2013-12-31T19:13:02Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.

	 lists [users] 2013-12-31T19:28:05Z Marge N. OXVera <marge@example.com>	# Adds table for storing lists.
	 hashtags [flips] 2013-12-31T19:30:13Z Marge N.	OXVera <marge@example.com> # Adds table	for storing hashtags.

       Note that it has	appended the changes from the merged "lists" branch,
       and then	merged the changes from	our "hashtags" branch. Test it to make
       sure it works as	expected:

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

       Note the	use of "rebase", which combines	a "revert" and a "deploy" into
       a single	command. Handy,	right? It correctly reverted our changes, and
       then deployed them all again in the proper order. So let's commit
       .gitattributes; seems worthwhile	to keep	that change:

	 > git add .
	 > git commit -m 'Add `.gitattributes` with union merge	for `sqitch.plan`.'
	 [hashtags 4f93ac4] Add	`.gitattributes` with union merge for `sqitch.plan`.
	  1 file changed, 1 insertion(+)
	  create mode 100644 .gitattributes

   Merges Mastered
       And now,	finally, we can	merge into "master":

	 > git checkout	master
	 Switched to branch 'master'
	 > git merge --no-ff hashtags -m "Merge	branch 'hashtags'"
	 Merge made by the 'recursive' strategy.
	  .gitattributes      |	 1 +
	  deploy/hashtags.sql |	12 ++++++++++++
	  revert/hashtags.sql |	 7 +++++++
	  sqitch.plan	      |	 1 +
	  verify/hashtags.sql |	 7 +++++++
	  5 files changed, 28 insertions(+)
	  create mode 100644 .gitattributes
	  create mode 100644 deploy/hashtags.sql
	  create mode 100644 revert/hashtags.sql
	  create mode 100644 verify/hashtags.sql

       And double-check	our work:

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

	 users 2013-12-31T18:06:04Z Marge N. OXVera <marge@example.com>	# Creates table	to track our users.
	 flips [users] 2013-12-31T19:01:40Z Marge N. OXVera <marge@example.com>	# Adds table for storing flips.
	 userflips [users flips] 2013-12-31T19:11:11Z Marge N. OXVera <marge@example.com> # Creates the	userflips view.
	 @v1.0.0-dev1 2013-12-31T19:13:02Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.

	 lists [users] 2013-12-31T19:28:05Z Marge N. OXVera <marge@example.com>	# Adds table for storing lists.
	 hashtags [flips] 2013-12-31T19:30:13Z Marge N.	OXVera <marge@example.com> # Adds table	for storing hashtags.

       Much much better, a nice	clean master now. And because it is now
       identical to the	"hashtags" branch, we can just carry on. Go ahead and
       tag it, bundle, and release:

	 > 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.'
	 [master 7abfd9b] Tag the database with	v1.0.0-dev2.
	  1 file 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
	   + users
	   + flips
	   + userflips @v1.0.0-dev1
	   + lists
	   + hashtags @v1.0.0-dev2

       Note the	use of the "--dest-dir"	option to "sqitch bundle". Just	a
       nicer way to create the top-level directory name	so we don't have to
       rename it from bundle.

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
       <http://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 master
	 # Your	branch is ahead	of 'origin/master' by 4	commits.
	 #   (use "git push" to	publish	your local commits)
	 #
	 # 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 are	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 won't be idempotent <http://en.wikipedia.org/wiki/Idempotence>
       -- that is, able	to be applied multiple times without changing the
       result beyond the initial application. It could be if SQLite supported
       "CREATE OR REPLACE VIEW", but since it doesn't, we will have to edit
       the script to drop the view before creating it. Or, more	simply,	it
       needs to	be updated to revert changes back to how they were as-of the
       deployment of deploy/userflips@v1.0.0-dev2.sql.

       Modify deploy/userflips.sql to add the "twitter"	column;	in fact, let's
       also add	a "DROP	VIEW IF	EXISTS"	statement, in case we need to rework
       this change again in the	future:

	 @@ -4,8 +4,9 @@

	  BEGIN;

	 +DROP VIEW IF EXISTS userflips;
	  CREATE VIEW userflips	AS
	 -SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
	 +SELECT f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp
	    FROM users u
	    JOIN flips f ON u.nickname = f.nickname;

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

	 @@ -2,7 +2,7 @@

	  BEGIN;

	 -SELECT id, nickname, fullname, body, timestamp
	 +SELECT id, nickname, fullname, twitter, body,	timestamp
	    FROM userflips
	   WHERE 0;

       And finally, modify revert/userflips@v1.0.0-dev2.sql to drop the	view
       before creating it:

	 @@ -4,6 +4,7 @@

	  BEGIN;

	 +DROP VIEW IF EXISTS userflips;
	  CREATE VIEW userflips	AS
	  SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
	    FROM users u

       Note that if we had included that statement when	we originally created
       the "userflips" change, we wouldn't have	to change this file at all.

       Now try a deployment:

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

       So, are the changes deployed?

	 > sqlite3 flipr_test.db '.schema userflips'
	 CREATE	VIEW userflips AS
	 SELECT	f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp
	   FROM	users u
	   JOIN	flips f	ON u.nickname =	f.nickname;

       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?

	 > sqlite3 flipr_test.db '.schema userflips'
	 CREATE	VIEW userflips AS
	 SELECT	f.id, u.nickname, u.fullname, f.body, f.timestamp
	       FROM users u
	       JOIN flips f ON u.nickname = f.nickname;

       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.'
	 [master 3eb96d9] Add the twitter column to the	userflips view.
	  7 files changed, 40 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) 2012-2015 iovation	Inc.

       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.

perl v5.24.1			  2017-07-03	      sqitchtutorial-sqlite(3)

Name | Synopsis | Description | Starting a New Project | Our First Change | On Target | Deploy with Dependency | View to a Thrill | Ship It! | Making a Hash of Things | In Place Changes | More to Come | Author | License

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