Allow passoing ExcludeConstraint to DropConstraint.from_constraint

Added support for ``op.drop_constraint()`` to support PostrgreSQL
``ExcludeConstraint`` objects, as well as other constraint-like objects
that may be present in third party dialects, by resolving the ``type_``
parameter to be ``None`` for this case.   Autogenerate has also been
enhanced to exclude the ``type_`` parameter from rendering within this
command when  ``type_`` is ``None``.  Pull request courtesy David Hills.

Fixes: #1300
Closes: #1301
Pull-request: #1301
Pull-request-sha: b8643d1

Change-Id: I25599d24a8bba455ab1d9b88843d8d84627a72d5

Author: DJHills

alembic/autogenerate/render.py

@@ -398,22 +398,21 @@ def _add_check_constraint(constraint, autogen_context):
 def _drop_constraint(
     autogen_context: AutogenContext, op: ops.DropConstraintOp
 ) -> str:
-    if autogen_context._has_batch:
-        template = "%(prefix)sdrop_constraint" "(%(name)r, type_=%(type)r)"
-    else:
-        template = (
-            "%(prefix)sdrop_constraint"
-            "(%(name)r, '%(table_name)s'%(schema)s, type_=%(type)r)"
-        )
+    prefix = _alembic_autogenerate_prefix(autogen_context)
+    name = _render_gen_name(autogen_context, op.constraint_name)
+    schema = _ident(op.schema) if op.schema else None
+    type_ = _ident(op.constraint_type) if op.constraint_type else None
 
-    text = template % {
-        "prefix": _alembic_autogenerate_prefix(autogen_context),
-        "name": _render_gen_name(autogen_context, op.constraint_name),
-        "table_name": _ident(op.table_name),
-        "type": op.constraint_type,
-        "schema": (", schema=%r" % _ident(op.schema)) if op.schema else "",
-    }
-    return text
+    params_strs = []
+    params_strs.append(repr(name))
+    if not autogen_context._has_batch:
+        params_strs.append(repr(_ident(op.table_name)))
+        if schema is not None:
+            params_strs.append(f"schema={schema!r}")
+    if type_ is not None:
+        params_strs.append(f"type_={type_!r}")
+
+    return f"{prefix}drop_constraint({', '.join(params_strs)})"
 
 
 @renderers.dispatch_for(ops.AddColumnOp)

alembic/operations/ops.py

@@ -171,7 +171,7 @@ def from_constraint(cls, constraint: Constraint) -> DropConstraintOp:
             sqla_compat.constraint_name_or_none(constraint.name),
             constraint_table.name,
             schema=constraint_table.schema,
-            type_=types[constraint.__visit_name__],
+            type_=types.get(constraint.__visit_name__),
             _reverse=AddConstraintOp.from_constraint(constraint),
         )
 

docs/build/unreleased/1300.rst

@@ -0,0 +1,12 @@
+.. change::
+    :tags: bug, operations
+    :tickets: 1300
+
+    Added support for ``op.drop_constraint()`` to support PostrgreSQL
+    ``ExcludeConstraint`` objects, as well as other constraint-like objects
+    that may be present in third party dialects, by resolving the ``type_``
+    parameter to be ``None`` for this case.   Autogenerate has also been
+    enhanced to exclude the ``type_`` parameter from rendering within this
+    command when  ``type_`` is ``None``.  Pull request courtesy David Hills.
+
+

tests/test_op.py

@@ -808,6 +808,11 @@ def test_drop_constraint_type(self):
         op.drop_constraint("foo_bar_bat", "t1", type_="foreignkey")
         context.assert_("ALTER TABLE t1 DROP CONSTRAINT foo_bar_bat")
 
+    def test_drop_constraint_type_generic(self):
+        context = op_fixture()
+        op.drop_constraint("foo_bar_bat", "t1")
+        context.assert_("ALTER TABLE t1 DROP CONSTRAINT foo_bar_bat")
+
     def test_drop_constraint_legacy_type(self):
         """#1245"""
         context = op_fixture()

tests/test_postgresql.py

@@ -1263,6 +1263,30 @@ def test_inline_exclude_constraint_text(self):
             "name='TExclID'))",
         )
 
+    def test_drop_exclude_constraint(self):
+        """test for #1300"""
+
+        autogen_context = self.autogen_context
+
+        m = MetaData()
+        t = Table(
+            "TTable", m, Column("XColumn", String), Column("YColumn", String)
+        )
+
+        op_obj = ops.DropConstraintOp.from_constraint(
+            ExcludeConstraint(
+                (t.c.XColumn, ">"),
+                where=t.c.XColumn != 2,
+                using="gist",
+                name="t_excl_x",
+            )
+        )
+
+        eq_ignore_whitespace(
+            autogenerate.render_op_text(autogen_context, op_obj),
+            "op.drop_constraint('t_excl_x', 'TTable')",
+        )
+
     def test_json_type(self):
         eq_ignore_whitespace(
             autogenerate.render._repr_type(JSON(), self.autogen_context),