Autoincrement via identity columns on PostgreSQL

[morozov]

Q	A
Type	improvement

See #4744. Fixes #3619, #4458, #4745, #5614 .

Note that in order to replicate the state of the serial column sequences in the identity columns, manual migration is required.
Without the above migration, the identity column sequences will be created from scratch and will produce values starting from 1.

The migration can be tested as:

1. Create a test schema and some data using DBAL 3:

   $schema = new Schema();
   $table = $schema->createTable('ai');
   $table->addColumn('id', 'integer', ['autoincrement' => true]);
   
   $sm = $connection->createSchemaManager();
   $sm->migrateSchema($schema);
   
   for ($i = 0; $i < 3; $i++) {
       $connection->executeStatement('INSERT INTO ai (id) VALUES (DEFAULT)');
   }

2. Confirm that the sequential numbers have been generated:

   SELECT id FROM ai;
   -- 1
   -- 2
   -- 3

3. Perform the migration:

   SELECT upgrade_serial_to_identity('ai', 'id');

4. Switch to DBAL 4.
5. Execute the script from step 1 again.
6. Confirm that the sequence is preserved:

   SELECT id FROM ai;
   -- 1
   -- 2
   -- 3
   -- 4
   -- 5
   -- 6

[morozov]

We need to move the migration steps to the documentation, although I'm not sure where exactly. @greg0ire do you have any ideas?

[greg0ire]

I guess you're implying these migration steps are too long to be included in UPGRADE.md? I think they would qualify as a how-to guide. Let's create docs/en/how-to and put them there, then? And then link to these docs from UPGRADE.md?

[greg0ire]

This simplifies the code nicely 🙂