- The "auto-attach" feature of constraints such as :class:`.UniqueConstraint`

and :class:`.CheckConstraint` has been further enhanced such that
when the constraint is associated with non-table-bound :class:`.Column`
objects, the constraint will set up event listeners with the
columns themselves such that the constraint auto attaches at the
same time the columns are associated with the table.  This in particular
helps in some edge cases in declarative but is also of general use.
fixes #3341

1 files changed, 37 insertions, 17 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index e022c5768..3aeba9804 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -2390,24 +2390,44 @@ class ColumnCollectionMixin(object):
         self._pending_colargs = [_to_schema_column_or_string(c)
                                  for c in columns]
         if _autoattach and self._pending_colargs:
-            columns = [
-                c for c in self._pending_colargs
-                if isinstance(c, Column) and
-                isinstance(c.table, Table)
-            ]
+            self._check_attach()
 
-            tables = set([c.table for c in columns])
-            if len(tables) == 1:
-                self._set_parent_with_dispatch(tables.pop())
-            elif len(tables) > 1 and not self._allow_multiple_tables:
-                table = columns[0].table
-                others = [c for c in columns[1:] if c.table is not table]
-                if others:
-                    raise exc.ArgumentError(
-                        "Column(s) %s are not part of table '%s'." %
-                        (", ".join("'%s'" % c for c in others),
-                            table.description)
-                    )
+    def _check_attach(self, evt=False):
+        col_objs = [
+            c for c in self._pending_colargs
+            if isinstance(c, Column)
+        ]
+        cols_w_table = [
+            c for c in col_objs if isinstance(c.table, Table)
+        ]
+        cols_wo_table = set(col_objs).difference(cols_w_table)
+
+        if cols_wo_table:
+            assert not evt, "Should not reach here on event call"
+
+            def _col_attached(column, table):
+                cols_wo_table.discard(column)
+                if not cols_wo_table:
+                    self._check_attach(evt=True)
+            self._cols_wo_table = cols_wo_table
+            for col in cols_wo_table:
+                col._on_table_attach(_col_attached)
+            return
+
+        columns = cols_w_table
+
+        tables = set([c.table for c in columns])
+        if len(tables) == 1:
+            self._set_parent_with_dispatch(tables.pop())
+        elif len(tables) > 1 and not self._allow_multiple_tables:
+            table = columns[0].table
+            others = [c for c in columns[1:] if c.table is not table]
+            if others:
+                raise exc.ArgumentError(
+                    "Column(s) %s are not part of table '%s'." %
+                    (", ".join("'%s'" % c for c in others),
+                        table.description)
+                )
 
     def _set_parent(self, table):
         for col in self._pending_colargs: