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Migration to identity columns on PostgreSQL

As of version 4, the DBAL uses identity columns to implement the autoincrement behavior on PostgreSQL instead of SERIAL* column types.

If you have a database with autoincrement columns created using DBAL 3 or earlier, you will need to perform the following schema migration before being able to continue managing the schema with the DBAL:

  1. Identify all autoincrement columns and their tables.
  2. Create the upgrade_serial_to_identity() function in the database as described in PostgreSQL 10 identity columns explained:

    1CREATE OR REPLACE FUNCTION upgrade_serial_to_identity(tbl regclass, col name) RETURNS void LANGUAGE plpgsql AS $$ DECLARE colnum smallint; seqid oid; count int; BEGIN -- find column number SELECT attnum INTO colnum FROM pg_attribute WHERE attrelid = tbl AND attname = col; IF NOT FOUND THEN RAISE EXCEPTION 'column does not exist'; END IF; -- find sequence SELECT INTO seqid objid FROM pg_depend WHERE (refclassid, refobjid, refobjsubid) = ('pg_class'::regclass, tbl, colnum) AND classid = 'pg_class'::regclass AND objsubid = 0 AND deptype = 'a'; GET DIAGNOSTICS count = ROW_COUNT; IF count < 1 THEN RAISE EXCEPTION 'no linked sequence found'; ELSIF count > 1 THEN RAISE EXCEPTION 'more than one linked sequence found'; END IF; -- drop the default EXECUTE 'ALTER TABLE ' || tbl || ' ALTER COLUMN ' || quote_ident(col) || ' DROP DEFAULT'; -- change the dependency between column and sequence to internal UPDATE pg_depend SET deptype = 'i' WHERE (classid, objid, objsubid) = ('pg_class'::regclass, seqid, 0) AND deptype = 'a'; -- mark the column as identity column UPDATE pg_attribute SET attidentity = 'd' WHERE attrelid = tbl AND attname = col; END; $$;
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  3. For each column and their table, run upgrade_serial_to_identity(<table>, <column>).

Without this migration, next time when DBAL 4 is used to manage the schema, it will perform a similar migration but instead of reusing the existing sequence, it will drop it and create a new one. As a result, all new sequence numbers will be generated from 1, which is most likely undesired.