- The MySQL dialect now supports CAST on types that are constructed

as :class:`.TypeDecorator` objects.

3 files changed, 23 insertions, 4 deletions

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index 1356c8eba..85681fbba 100644
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -25,6 +25,12 @@
 
     .. change::
         :tags: bug, mysql
+
+        The MySQL dialect now supports CAST on types that are constructed
+        as :class:`.TypeDecorator` objects.
+
+    .. change::
+        :tags: bug, mysql
         :tickets: 3237
 
         A warning is emitted when :func:`.cast` is used with the MySQL
diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 0a999a85f..0d2c36189 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -1683,9 +1683,12 @@ class MySQLCompiler(compiler.SQLCompiler):
     def get_from_hint_text(self, table, text):
         return text
 
-    def visit_typeclause(self, typeclause):
-        type_ = typeclause.type.dialect_impl(self.dialect)
-        if isinstance(type_, sqltypes.Integer):
+    def visit_typeclause(self, typeclause, type_=None):
+        if type_ is None:
+            type_ = typeclause.type.dialect_impl(self.dialect)
+        if isinstance(type_, sqltypes.TypeDecorator):
+            return self.visit_typeclause(typeclause, type_.impl)
+        elif isinstance(type_, sqltypes.Integer):
             if getattr(type_, 'unsigned', False):
                 return 'UNSIGNED INTEGER'
             else:
diff --git a/test/dialect/mysql/test_compiler.py b/test/dialect/mysql/test_compiler.py
index 23341b9d2..304c31012 100644
--- a/test/dialect/mysql/test_compiler.py
+++ b/test/dialect/mysql/test_compiler.py
@@ -392,11 +392,22 @@ class SQLTest(fixtures.TestBase, AssertsCompiledSQL):
             (m.MSVarBinary, "CAST(t.col AS BINARY)"),
             (m.MSVarBinary(32), "CAST(t.col AS BINARY)"),
 
+            (Interval, "CAST(t.col AS DATETIME)"),
+
         ]
 
         for type_, expected in specs:
             self.assert_compile(cast(t.c.col, type_), expected)
 
+    def test_cast_type_decorator(self):
+        class MyInteger(sqltypes.TypeDecorator):
+            impl = Integer
+
+        type_ = MyInteger()
+        t = sql.table('t', sql.column('col'))
+        self.assert_compile(
+            cast(t.c.col, type_), "CAST(t.col AS SIGNED INTEGER)")
+
     def test_unsupported_casts(self):
 
         t = sql.table('t', sql.column('col'))
@@ -413,7 +424,6 @@ class SQLTest(fixtures.TestBase, AssertsCompiledSQL):
 
             (m.MSYear, "t.col"),
             (m.MSYear(2), "t.col"),
-            (Interval, "t.col"),
 
             (Boolean, "t.col"),
             (BOOLEAN, "t.col"),