Skip UniqueConstraint marked by unique=True in tometadata

Fixes an issue where a Column would be copied with unique=True
and at the same time the UniqueConstraint would also be copied,
leading to duplicate UniqueConstraints in the target table,
when tometadata() is used.   Imitates the same logic used
by index=True/Index to avoid duplicates.  For some reason
a fix was implemented for Index long ago but never for
UniqueConstraint.

Change-Id: Ie622ee912a6fb8bf0ea900a8b09d78c7ebc79fc0
Fixes: #3721

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index 5f9521c4792778beaedb569afbf499ea3427b7e2..b59ab392e548707fe34e0fedacdf99aca1cef770 100644 (file)
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -18,6 +18,14 @@
 .. changelog::
     :version: 1.0.14
 
+    .. change::
+        :tags: bug, sql
+        :tickets: 3721
+
+        Fixed bug whereby :meth:`.Table.tometadata` would make a duplicate
+        :class:`.UniqueConstraint` for each :class:`.Column` object that
+        featured the ``unique=True`` parameter.
+
     .. change::
         :tags: bug, engine, postgresql
         :tickets: 3716

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index 64692644cf4ef023fa8183449e951ca9f156b3a7..cb01a49e36c57198fae4ea8be20583ab8a073aad 100644 (file)
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -852,8 +852,14 @@ class Table(DialectKWArgs, SchemaItem, TableClause):
                         schema if referred_schema == self.schema else None)
                 table.append_constraint(
                     c.copy(schema=fk_constraint_schema, target_table=table))
-
             elif not c._type_bound:
+                # skip unique constraints that would be generated
+                # by the 'unique' flag on Column
+                if isinstance(c, UniqueConstraint) and \
+                    len(c.columns) == 1 and \
+                        list(c.columns)[0].unique:
+                    continue
+
                 table.append_constraint(
                     c.copy(schema=schema, target_table=table))
         for index in self.indexes:

diff --git a/test/sql/test_metadata.py b/test/sql/test_metadata.py
index 449956fcd46f889f98c56a7d38a2ec0f731a33d7..344cfefa5eae7ef65034409d9ea1156431b67859 100644 (file)
--- a/test/sql/test_metadata.py
+++ b/test/sql/test_metadata.py
@@ -1113,6 +1113,34 @@ class ToMetaDataTest(fixtures.TestBase, ComparesTables):
         eq_(str(table_c.join(table2_c).onclause),
             'mytable.myid = othertable.myid')
 
+    def test_unique_true_flag(self):
+        meta = MetaData()
+
+        table = Table('mytable', meta, Column('x', Integer, unique=True))
+
+        m2 = MetaData()
+
+        t2 = table.tometadata(m2)
+
+        eq_(
+            len([
+                const for const
+                in t2.constraints
+                if isinstance(const, UniqueConstraint)]),
+            1
+        )
+
+    def test_index_true_flag(self):
+        meta = MetaData()
+
+        table = Table('mytable', meta, Column('x', Integer, index=True))
+
+        m2 = MetaData()
+
+        t2 = table.tometadata(m2)
+
+        eq_(len(t2.indexes), 1)
+
 
 class InfoTest(fixtures.TestBase):
     def test_metadata_info(self):