Remove ORM elements from annotations at the schema level.

Fixed issue where when constructing constraints from ORM-bound columns,
primarily :class:`.ForeignKey` objects but also :class:`.UniqueConstraint`,
:class:`.CheckConstraint` and others, the ORM-level
:class:`.InstrumentedAttribute` is discarded entirely, and all ORM-level
annotations from the columns are removed; this is so that the constraints
are still fully pickleable without the ORM-level entities being pulled in.
These annotations are not necessary to be present at the schema/metadata
level.

Fully implemented coercions for constraint columns within
schema.py, including for FK referenced columns.

Fixes: #5001
Change-Id: I895400dd979310be034085d207f096707c635909

1 files changed, 15 insertions, 2 deletions

diff --git a/lib/sqlalchemy/sql/coercions.py b/lib/sqlalchemy/sql/coercions.py
index 95aee0468..b45ef3991 100644
--- a/lib/sqlalchemy/sql/coercions.py
+++ b/lib/sqlalchemy/sql/coercions.py
@@ -147,6 +147,13 @@ class RoleImpl(object):
         raise exc.ArgumentError(msg, code=code)
 
 
+class _Deannotate(object):
+    def _post_coercion(self, resolved, **kw):
+        from .util import _deep_deannotate
+
+        return _deep_deannotate(resolved)
+
+
 class _StringOnly(object):
     def _resolve_for_clause_element(self, element, argname=None, **kw):
         return self._literal_coercion(element, **kw)
@@ -461,7 +468,9 @@ class TruncatedLabelImpl(_StringOnly, RoleImpl, roles.TruncatedLabelRole):
             return elements._truncated_label(element)
 
 
-class DDLExpressionImpl(_CoerceLiterals, RoleImpl, roles.DDLExpressionRole):
+class DDLExpressionImpl(
+    _Deannotate, _CoerceLiterals, RoleImpl, roles.DDLExpressionRole
+):
 
     _coerce_consts = True
 
@@ -470,11 +479,15 @@ class DDLExpressionImpl(_CoerceLiterals, RoleImpl, roles.DDLExpressionRole):
 
 
 class DDLConstraintColumnImpl(
-    _ReturnsStringKey, RoleImpl, roles.DDLConstraintColumnRole
+    _Deannotate, _ReturnsStringKey, RoleImpl, roles.DDLConstraintColumnRole
 ):
     pass
 
 
+class DDLReferredColumnImpl(DDLConstraintColumnImpl):
+    pass
+
+
 class LimitOffsetImpl(RoleImpl, roles.LimitOffsetRole):
     def _implicit_coercions(self, element, resolved, argname=None, **kw):
         if resolved is None: