Update migration query to make it work with existing view (#2308)

Signed-off-by: Minkyu Park <minkyu.park.200@gmail.com>

Signed-off-by: Minkyu Park <minkyu.park.200@gmail.com>

Author: fm100

api/src/main/resources/marquez/db/migration/V52__alter_dataset_symlinks.sql

@@ -1,2 +1,28 @@
 /* SPDX-License-Identifier: Apache-2.0 */
-ALTER TABLE dataset_symlinks ALTER COLUMN name TYPE VARCHAR;
+
+DO
+$$
+DECLARE
+    datasets_view_exists boolean;
+    datasets_view_definition text;
+BEGIN
+    SELECT EXISTS (
+        SELECT * FROM information_schema.views
+        WHERE table_schema='public' AND table_name='datasets_view'
+    ) INTO datasets_view_exists;
+
+    IF datasets_view_exists THEN
+        -- Altering is not allowed when the column is being used from views. So here,
+        -- we temporarily drop the view before altering and recreate it.
+        SELECT view_definition FROM information_schema.views
+        WHERE table_schema='public' AND table_name='datasets_view'
+        INTO datasets_view_definition;
+
+        DROP VIEW datasets_view;
+        ALTER TABLE dataset_symlinks ALTER COLUMN name TYPE VARCHAR;
+        EXECUTE format('CREATE VIEW datasets_view AS %s', datasets_view_definition);
+    ELSE
+        ALTER TABLE dataset_symlinks ALTER COLUMN name TYPE VARCHAR;
+    END IF;
+END
+$$ LANGUAGE plpgsql;