Postgres examples #732

peterbecich · 2024-12-14T06:31:54Z

This PR adds two executables to the Postgres Pagila example.

cabal run prints the migration to the screen to help understanding.

$ cabal run
Migration steps:
Initial commit
Add film actor, inventory, rental table
-------------
For each migration step, the sequence of SQL scripts:
Initial commit
SQL command type: PgCommandTypeDdl
SQL script: 
CREATE TABLE "actor" ("actor_id" SERIAL, "first_name" VARCHAR(45) NOT NULL, "last_name" VARCHAR(45) NOT NULL UNIQUE, "last_update" TIMESTAMP DEFAULT NOW() NOT NULL, PRIMARY KEY("actor_id")) 
SQL command type: PgCommandTypeDdl
SQL script: 
CREATE TABLE "address" ("address_id" SMALLSERIAL, "address" VARCHAR(50) NOT NULL, "address2" VARCHAR(50), "district" VARCHAR(20) NOT NULL, "city_id" SMALLINT NOT NULL, "postal_code" VARCHAR(10), "phone" VARCHAR(20) NOT NULL, "last_update" TIMESTAMP DEFAULT NOW() NOT NULL, PRIMARY KEY("address_id")) 
SQL command type: PgCommandTypeDdl
SQL script: 
CREATE TABLE "city" ("city_id" SMALLINT, "city" VARCHAR(50) NOT NULL, "country_id" SMALLINT NOT NULL, "last_update" TIMESTAMP DEFAULT NOW() NOT NULL, PRIMARY KEY("city_id")) 
SQL command type: PgCommandTypeDdl
SQL script: 
CREATE TABLE "country" ("country_id" SMALLINT, "country" VARCHAR(50) NOT NULL, "last_update" TIMESTAMP DEFAULT NOW() NOT NULL, PRIMARY KEY("country_id")) 
.
.
.
.

cabal run pagila-migration
This applies the migration to a Postgres instance. It will overwrite the data in this Postgres instance. This is documented: https://github.com/haskell-beam/beam/blob/867fc8ae1ebbcc3b5832300a7492516902af3206/beam-postgres/examples/readme.md#pagila-example

The migration example will generate countries and staff and insert them into the database after migration V0001. Then V0002 migration is applied and the staff are migrated to V0002.NewStaff.

peterbecich · 2025-01-19T19:14:07Z

@LaurentRDC , this PR makes the example schema usable. The user must provide the instance of Postgres to target.

It also generates random data to populate the database with rows. There is a safety check for the user before any change is applied to the database.

peterbecich · 2025-02-22T06:36:47Z

@LaurentRDC please review, can I help in any way? Do you want the data generation removed?

LaurentRDC · 2024-12-14T20:50:22Z

beam-postgres/examples/app/Main.hs

+  putStrLn "-------------"
+  putStrLn "For each migration step, the sequence of SQL scripts:"
+  let
+    renderer :: BeamSqlBackendSyntax Postgres -> String


As mentioned in the documentation for backendMigrationStepsScript, why not use displaySyntax, which has type Syntax -> String?

Recall that BeamSqlBackendSyntax Postgres is PgSyntax, and PgSyntax has an instance of Sql92DisplaySyntax such that displaySyntax will work

I need more time to understand this, can it be moved to a follow-up issue?

Iinsist on using displaySyntax. We want to show the appropriate, canonical way to do things in this example.

LaurentRDC · 2024-12-14T20:52:55Z

beam-postgres/examples/readme.md

@@ -0,0 +1,3 @@
+# Pagila example
+
+`cabal run` to see rendering of Postgres migration.


In the future, if there are more executables, cabal run won't be able to determine which executable is implied.

From the root of the repository, you refer users to run cabal run pagila instead of cabal run

You're right, it should be cabal run pagila-print. Fixed. There is no target for cabal run.

beam-postgres/examples/pagila.cabal

beam-core/Database/Beam/Backend/SQL/Types.hs

LaurentRDC · 2025-02-22T15:42:59Z

Hi Peter, I started the review weeks ago, but apparently never pressed the "finish review" button. Sorry!

`cabal run` in `pagila` package

peterbecich · 2025-02-23T07:45:52Z

Thank you @LaurentRDC

LaurentRDC · 2025-02-24T00:24:51Z

beam-migrate/Database/Beam/Migrate/Simple.hs

+-- | Given a function to convert a command to a 'String', produce a script that
+-- will execute the given migration steps. Usually, the function you provide
+-- eventually calls 'displaySyntax' to render the command.
+backendMigrationStepsScript :: BeamSqlBackend be


Can you mention backendMigrationScript in the docstring for backendMigrationStepsScript, and vice-versa? This way, users can more easily navigate the documentation

LaurentRDC · 2025-02-24T00:33:46Z

beam-postgres/examples/src/Pagila/Schema/V0001.hs

+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE DerivingVia #-}


I don't think deriving strategies are used anymore in this changeset

LaurentRDC · 2025-02-24T00:34:38Z

docs/user-guide/custom-type-migration.md

@@ -1,4 +1,4 @@
-**Note**: The code used in this guide is in `beam-postgres/examples/Pagila/Schema/CustomMigrateExample.hs`.
+**Note**: The code used in this guide is in the `pagila.cabal` package, located in `beam-postgres/examples/`. `cabal run pagila` to see a rendering of the example schema.


I think you mean cabal run pagila-print to see a rendering of ....

peterbecich mentioned this pull request Dec 23, 2024

demonstrate alterTable and addColumn in example migration #733

Merged

peterbecich force-pushed the postgres-example-executable branch from 01c842e to 867fc8a Compare December 23, 2024 08:48

peterbecich changed the title ~~Postgres example executable~~ Postgres examples Dec 23, 2024

LaurentRDC self-requested a review December 24, 2024 19:00

peterbecich force-pushed the postgres-example-executable branch 6 times, most recently from d2a78e4 to 4bd1773 Compare December 25, 2024 22:16

LaurentRDC reviewed Feb 22, 2025

View reviewed changes

peterbecich added 6 commits February 22, 2025 23:14

runnable example migration

2ba780b

`cabal run` in `pagila` package

doc pagila.cabal

3e6a400

example applies migration to real Postgres instance

b20fbee

migration example safety check

072937d

ensure pagila-migration example is not default executable

df858c3

generate arbitrary data for example

ba070df

peterbecich force-pushed the postgres-example-executable branch from 4bd1773 to ba070df Compare February 23, 2025 07:14

fix Pagila example readme

338d2a2

peterbecich requested a review from LaurentRDC February 23, 2025 07:45

LaurentRDC requested changes Feb 24, 2025

View reviewed changes

		@@ -0,0 +1,3 @@
		# Pagila example

		`cabal run` to see rendering of Postgres migration.

		{-# LANGUAGE DerivingStrategies #-}
		{-# LANGUAGE DerivingVia #-}

		@@ -1,4 +1,4 @@
		Note: The code used in this guide is in `beam-postgres/examples/Pagila/Schema/CustomMigrateExample.hs`.
		Note: The code used in this guide is in the `pagila.cabal` package, located in `beam-postgres/examples/`. `cabal run pagila` to see a rendering of the example schema.

Postgres examples #732

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LaurentRDC commented Feb 22, 2025

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peterbecich commented Dec 14, 2024 •

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