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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:

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

  3. Run the function for each table like this:

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

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.