Fix down SQL for removing columns

migration/sort_title.12.cr

@@ -9,9 +9,86 @@ class SortTitle < MG::Base
 
   def down : String
     <<-SQL
-    -- drop sort_title column to ids and titles
-    ALTER TABLE ids DROP COLUMN sort_title;
-    ALTER TABLE titles DROP COLUMN sort_title;
+    -- remove sort_title column from ids
+    ALTER TABLE ids RENAME TO tmp;
+
+    CREATE TABLE ids (
+      path TEXT NOT NULL,
+      id TEXT NOT NULL,
+      signature TEXT,
+      unavailable INTEGER NOT NULL DEFAULT 0
+    );
+
+    INSERT INTO ids
+    SELECT path, id, signature, unavailable
+    FROM tmp;
+
+    DROP TABLE tmp;
+
+    -- recreate the indices
+    CREATE UNIQUE INDEX path_idx ON ids (path);
+    CREATE UNIQUE INDEX id_idx ON ids (id);
+
+    -- recreate the foreign key constraint on thumbnails
+    ALTER TABLE thumbnails RENAME TO tmp;
+
+    CREATE TABLE thumbnails (
+      id TEXT NOT NULL,
+      data BLOB NOT NULL,
+      filename TEXT NOT NULL,
+      mime TEXT NOT NULL,
+      size INTEGER NOT NULL,
+      FOREIGN KEY (id) REFERENCES ids (id)
+        ON UPDATE CASCADE
+        ON DELETE CASCADE
+    );
+
+    INSERT INTO thumbnails
+    SELECT * FROM tmp;
+
+    DROP TABLE tmp;
+
+    CREATE UNIQUE INDEX tn_index ON thumbnails (id);
+
+    -- remove sort_title column from titles
+    ALTER TABLE titles RENAME TO tmp;
+
+    CREATE TABLE titles (
+      id TEXT NOT NULL,
+      path TEXT NOT NULL,
+      signature TEXT,
+      unavailable INTEGER NOT NULL DEFAULT 0
+    );
+
+    INSERT INTO titles
+    SELECT path, id, signature, unavailable
+    FROM tmp;
+
+    DROP TABLE tmp;
+
+    -- recreate the indices
+    CREATE UNIQUE INDEX titles_id_idx on titles (id);
+    CREATE UNIQUE INDEX titles_path_idx on titles (path);
+
+    -- recreate the foreign key constraint on tags
+    ALTER TABLE tags RENAME TO tmp;
+
+    CREATE TABLE tags (
+      id TEXT NOT NULL,
+      tag TEXT NOT NULL,
+      UNIQUE (id, tag),
+      FOREIGN KEY (id) REFERENCES titles (id)
+        ON UPDATE CASCADE
+        ON DELETE CASCADE
+    );
+
+    INSERT INTO tags
+    SELECT * FROM tmp;
+
+    DROP TABLE tmp;
+
+    CREATE INDEX tags_id_idx ON tags (id);
+    CREATE INDEX tags_tag_idx ON tags (tag);
     SQL
   end
 end