Fix duplicated constraints when using expressions

Fixed issue where using :meth:`.Operations.create_table` in conjunction
with a :class:`.CheckConstraint` that referred to table-bound
:class:`.Column` objects rather than string expressions would be added to
the parent table twice, resulting in an incorrect DDL sequence. Pull
request courtesy Nicolas CANIART.

Fixes: #1004
Closes: #1005
Pull-request: https://github.com/sqlalchemy/alembic/pull/1005
Pull-request-sha: 2fe5c5297bcde990096571a047039c451aa876f6

Change-Id: I2bf48701968fe59a6766f8f8879320b1bfd75774

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/test_op.py b/tests/test_op.py
index 11d2c1b..677b7bc 100644
--- a/tests/test_op.py
+++ b/tests/test_op.py
@@ -882,6 +882,27 @@ class OpTest(TestBase):
         ck = [c for c in t1.constraints if isinstance(c, CheckConstraint)]
         eq_(ck[0].name, "ck_1")
 
+    def test_create_table_with_check_constraint_with_expr(self):
+        context = op_fixture()
+        foo_id = Column("foo_id", Integer)
+        t1 = op.create_table(
+            "some_table",
+            Column("id", Integer, primary_key=True),
+            foo_id,
+            CheckConstraint(foo_id > 5, name="ck_1"),
+        )
+        context.assert_(
+            "CREATE TABLE some_table ("
+            "id INTEGER NOT NULL, "
+            "foo_id INTEGER, "
+            "PRIMARY KEY (id), "
+            "CONSTRAINT ck_1 CHECK (foo_id > 5))"
+        )
+
+        ck = [c for c in t1.constraints if isinstance(c, CheckConstraint)]
+        eq_(ck[0].name, "ck_1")
+        eq_(len(ck), 1)
+
     def test_create_table_unique_constraint(self):
         context = op_fixture()
         t1 = op.create_table(