Fix error when altering Part table that uses "master" keyword

CHANGELOG.md

@@ -1,5 +1,8 @@
 ## Release notes
 
+### Upcoming
+- Fixed - Fix altering a part table that uses the "master" keyword - PR [#991](https://github.com/datajoint/datajoint-python/pull/991)
+
 ### 0.14.0 -- Feb 13, 2023
 - Added - `json` data type ([#245](https://github.com/datajoint/datajoint-python/issues/245)) PR [#1051](https://github.com/datajoint/datajoint-python/pull/1051)
 - Fixed - Activating a schema requires all tables to exist even if `create_tables=False` PR [#1058](https://github.com/datajoint/datajoint-python/pull/1058)

datajoint/user_tables.py

@@ -238,3 +238,7 @@ def drop(self, force=False):
             raise DataJointError(
                 "Cannot drop a Part directly.  Delete from master instead"
             )
+
+    def alter(self, prompt=True, context=None):
+        # without context, use declaration context which maps master keyword to master table
+        super().alter(prompt=prompt, context=context or self.declaration_context)

tests/test_alter.py

@@ -1,4 +1,5 @@
 from nose.tools import assert_equal, assert_not_equal
+import re
 from .schema import *
 
 
@@ -27,6 +28,33 @@ class Experiment(dj.Imported):
     """
 
 
+@schema
+class Parent(dj.Manual):
+    definition = """
+    parent_id: int
+    """
+
+    class Child(dj.Part):
+        definition = """
+        -> Parent
+        """
+        definition_new = """
+        -> master
+        ---
+        child_id=null: int
+        """
+
+    class Grandchild(dj.Part):
+        definition = """
+        -> master.Child
+        """
+        definition_new = """
+        -> master.Child
+        ---
+        grandchild_id=null: int
+        """
+
+
 def test_alter():
     original = schema.connection.query(
         "SHOW CREATE TABLE " + Experiment.full_table_name
@@ -44,3 +72,25 @@ def test_alter():
     ).fetchone()[1]
     assert_not_equal(altered, restored)
     assert_equal(original, restored)
+
+
+def test_alter_part():
+    # https://github.com/datajoint/datajoint-python/issues/936
+
+    def verify_alter(table, attribute_sql):
+        definition_original = schema.connection.query(
+            f"SHOW CREATE TABLE {table.full_table_name}"
+        ).fetchone()[1]
+        table.definition = table.definition_new
+        table.alter(prompt=False)
+        definition_new = schema.connection.query(
+            f"SHOW CREATE TABLE {table.full_table_name}"
+        ).fetchone()[1]
+        assert (
+            re.sub(f"{attribute_sql},\n  ", "", definition_new) == definition_original
+        )
+
+    verify_alter(table=Parent.Child, attribute_sql="`child_id` .* DEFAULT NULL")
+    verify_alter(
+        table=Parent.Grandchild, attribute_sql="`grandchild_id` .* DEFAULT NULL"
+    )