cast json values on write to be consistent with reading from the db.

See also commit 5ac2341fab

activerecord/CHANGELOG.md

@@ -1,3 +1,18 @@
+*   Type cast json values on write, so that the value is consistent
+    with reading from the database.
+
+    Example:
+
+        x = JsonDataType.new tags: {"string" => "foo", :symbol => :bar}
+
+        # Before:
+        x.tags # => {"string" => "foo", :symbol => :bar}
+
+        # After:
+        x.tags # => {"string" => "foo", "symbol" => "bar"}
+
+    *Severin Schoepke*
+
 *   `ActiveRecord::Store` works together with PG `hstore` columns.
     Fixes #12452.
 

activerecord/lib/active_record/connection_adapters/postgresql/oid.rb

@@ -249,6 +249,10 @@ module ActiveRecord
         end
 
         class Json < Type
+          def type_cast_for_write(value)
+            ConnectionAdapters::PostgreSQLColumn.json_to_string value
+          end
+
           def type_cast(value)
             return if value.nil?
 

activerecord/test/cases/adapters/postgresql/json_test.rb

@@ -49,6 +49,13 @@ class PostgresqlJSONTest < ActiveRecord::TestCase
     JsonDataType.reset_column_information
   end
 
+  def test_cast_value_on_write
+    x = JsonDataType.new payload: {"string" => "foo", :symbol => :bar}
+    assert_equal({"string" => "foo", "symbol" => "bar"}, x.payload)
+    x.save
+    assert_equal({"string" => "foo", "symbol" => "bar"}, x.reload.payload)
+  end
+
   def test_type_cast_json
     assert @column