Add DROP CONSTRAINT to MySQL for mariadb

Added support for DROP CONSTRAINT to the MySQL Alembic
dialect to support MariaDB 10.2 which now has real
CHECK constraints.  Note this change does **not**
add autogenerate support, only support for op.drop_constraint()
to work.

Change-Id: I15b2425a44e4559b047b61573117fca9a46c8be3
Fixes: #479

diff --git a/alembic/ddl/mysql.py b/alembic/ddl/mysql.py
index aff7561a56e90d5066d515a198e16158577bd538..71b186cd75f344fd7c86d450737a97c5643142da 100644 (file)
--- a/alembic/ddl/mysql.py
+++ b/alembic/ddl/mysql.py
@@ -333,8 +333,11 @@ def _mysql_drop_constraint(element, compiler, **kw):
                   ):
         return compiler.visit_drop_constraint(element, **kw)
     elif isinstance(constraint, schema.CheckConstraint):
-        raise NotImplementedError(
-            "MySQL does not support CHECK constraints.")
+        # note that SQLAlchemy as of 1.2 does not yet support
+        # DROP CONSTRAINT for MySQL/MariaDB, so we implement fully
+        # here.
+        return "ALTER TABLE %s DROP CONSTRAINT %s" % \
+            (compiler.preparer.format_table(constraint.table), constraint.name)
     else:
         raise NotImplementedError(
             "No generic 'DROP CONSTRAINT' in MySQL - "

diff --git a/docs/build/unreleased/479.rst b/docs/build/unreleased/479.rst
new file mode 100644 (file)
index 0000000..feebb89
--- /dev/null
+++ b/docs/build/unreleased/479.rst
@@ -0,0 +1,9 @@
+.. change::
+    :tags: bug, mysql
+    :tickets: 479
+
+    Added support for DROP CONSTRAINT to the MySQL Alembic
+    dialect to support MariaDB 10.2 which now has real
+    CHECK constraints.  Note this change does **not**
+    add autogenerate support, only support for op.drop_constraint()
+    to work.

diff --git a/tests/test_mysql.py b/tests/test_mysql.py
index ac20f9bcaba59047964e98d1814f8c5c3cd7791f..e7b1cf08c32d93c27d1571fa53dc891ff167b792 100644 (file)
--- a/tests/test_mysql.py
+++ b/tests/test_mysql.py
@@ -189,11 +189,10 @@ class MySQLOpTest(TestBase):
         )
 
     def test_drop_check(self):
-        op_fixture('mysql')
-        assert_raises_message(
-            NotImplementedError,
-            "MySQL does not support CHECK constraints.",
-            op.drop_constraint, "f1", "t1", "check"
+        context = op_fixture('mysql')
+        op.drop_constraint("f1", "t1", "check")
+        context.assert_(
+            "ALTER TABLE t1 DROP CONSTRAINT f1"
         )
 
     def test_drop_unknown(self):