Upgrade PostgreSQL serial to identity columns function

Function to help update PostgreSQL serial columns to identity

4dev/database/function/upgrade_serial_to_identity.sql

@@ -0,0 +1,105 @@
+-- Upgrae serial to identity type
+--
+-- @param reclass tbl The table where the column is located
+-- @param name col The column to be changed
+-- @param varchar identity_type [default=a] Allowed a, d, assigned, default
+-- @param varchar col_type [default=''] Allowed smallint, int, bigint, int2, int4, int8
+-- @raises EXCEPTON on column not found, no linked sequence, more than one linked sequence found
+--
+CREATE OR REPLACE FUNCTION upgrade_serial_to_identity(
+    tbl regclass,
+    col name,
+    identity_type varchar = 'a',
+    col_type varchar = ''
+)
+RETURNS void
+LANGUAGE plpgsql
+AS $$
+DECLARE
+colnum smallint;
+seqid oid;
+count int;
+col_type_oid int;
+col_type_len int;
+current_col_atttypid oid;
+current_col_attlen int;
+BEGIN
+    -- switch between always (default) or default identiy type
+    IF identity_type NOT IN ('a', 'd', 'assigned', 'default') THEN
+        identity_type := 'a';
+    ELSE
+        IF identity_type = 'default' THEN
+            identity_type := 'd';
+        ELSIF identity_type = 'assigned' THEN
+            identity_type := 'a';
+        END IF;
+    END IF;
+    -- find column number, attribute oid and attribute len
+    SELECT attnum, atttypid, attlen
+        INTO colnum, current_col_atttypid, current_col_attlen
+        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 to 'd' for default
+        SET attidentity = identity_type
+        WHERE attrelid = tbl
+            AND attname = col;
+    RAISE NOTICE 'Update to identity for table "%" and columen "%" with type "%"', tbl, col, identity_type;
+
+    -- set type if requested and not empty
+    IF col_type <> '' THEN
+        IF col_type IN ('smallint', 'int', 'bigint', 'int2', 'int4', 'int8') THEN
+            -- rewrite smallint, int, bigint
+            IF col_type = 'smallint' THEN
+                col_type := 'int2';
+            ELSIF col_type = 'int' THEN
+                col_type := 'int4';
+            ELSIF col_type = 'bigint' THEN
+                col_type := 'int8';
+            END IF;
+            -- get the length and oid for selected
+            SELECT oid, typlen INTO col_type_oid, col_type_len FROM pg_type WHERE typname = col_type;
+            -- set only if diff or hight
+            IF current_col_atttypid <> col_type_oid AND col_type_len > current_col_attlen THEN
+                RAISE NOTICE 'Change col type: %', col_type;
+                -- update type
+                UPDATE pg_attribute
+                    SET
+                        atttypid = col_type_oid, attlen = col_type_len
+                    WHERE attrelid = tbl
+                        AND attname = col;
+            END IF;
+        ELSE
+            RAISE NOTICE 'Invalid col type: %', col_type;
+        END IF;
+    END IF;
+END;
+$$;