Add ability to use custom raw sql for `backfill_column_for_type_chang…

…e`'s `type_cast_function`

Fixes #36.

CHANGELOG.md

@@ -1,5 +1,11 @@
 ## master (unreleased)
 
+- Add ability to use custom raw sql for `backfill_column_for_type_change`'s `type_cast_function`
+
+    ```ruby
+    backfill_column_for_type_change(:users, :company_id, type_cast_function: Arel.sql("company_id::integer"))
+    ```
+
 - Fix version safety with `revert`
 
 ## 0.8.2 (2023-09-26)

lib/online_migrations/change_column_type_helpers.rb

@@ -176,6 +176,7 @@ def revert_initialize_columns_type_change(table_name, columns_and_types, **_opti
     #
     # @example With type casting
     #   backfill_column_for_type_change(:users, :settings, type_cast_function: "jsonb")
+    #   backfill_column_for_type_change(:users, :company_id, type_cast_function: Arel.sql("company_id::integer"))
     #
     # @example Additional batch options
     #   backfill_column_for_type_change(:files, :size, batch_size: 10_000)
@@ -202,7 +203,13 @@ def backfill_columns_for_type_change(table_name, *column_names, type_cast_functi
 
         old_value = Arel::Table.new(table_name)[column_name]
         if (type_cast_function = type_cast_functions.with_indifferent_access[column_name])
-          old_value = Arel::Nodes::NamedFunction.new(type_cast_function.to_s, [old_value])
+          old_value =
+            case type_cast_function
+            when Arel::Nodes::SqlLiteral
+              type_cast_function
+            else
+              Arel::Nodes::NamedFunction.new(type_cast_function.to_s, [old_value])
+            end
         end
 
         [tmp_column, old_value]

test/schema_statements/changing_column_type_test.rb

@@ -28,6 +28,7 @@ def setup
         t.text :settings
         t.bigint :star_count
         t.integer :user_id
+        t.string :company_id
 
         t.index :name
         t.foreign_key :users
@@ -207,6 +208,15 @@ def test_backfill_column_for_type_change_type_cast_function
       assert_equal "value", p.reload.settings["key"]
     end
 
+    def test_backfill_column_for_type_change_type_cast_function_as_literal
+      clear_caches
+      p = Project.create!(description: "Required description", company_id: "1")
+
+      change_column_type(:projects, :company_id, :integer, type_cast_function: Arel.sql("company_id::integer"))
+      Project.reset_column_information
+      assert_equal 1, p.reload.company_id
+    end
+
     def test_backfill_column_for_type_change_in_background
       @connection.initialize_column_type_change(:projects, :name, :string)
       m = @connection.backfill_column_for_type_change_in_background(