Accommodate column-based naming conventions for pk constraint

Repaired / implemented support for primary key constraint naming
conventions that use column names/keys/etc as part of the convention. In
particular, this includes that the :class:`.PrimaryKeyConstraint` object
that's automatically associated with a :class:`.schema.Table` will update
its name as new primary key :class:`_schema.Column` objects are added to
the table and then to the constraint. Internal failure modes related to
this constraint construction process including no columns present, no name
present or blank name present are now accommodated.

Fixes: #5919
Change-Id: Ic2800b50f4a4cd5978bec48cefea0a2e198e0123

3 files changed, 47 insertions, 11 deletions

diff --git a/lib/sqlalchemy/sql/events.py b/lib/sqlalchemy/sql/events.py
index deaa992af..18c0e8c60 100644
--- a/lib/sqlalchemy/sql/events.py
+++ b/lib/sqlalchemy/sql/events.py
@@ -209,6 +209,12 @@ class DDLEvents(event.Events):
 
         """
 
+    def _sa_event_column_added_to_pk_constraint(self, const, col):
+        """internal event hook used for primary key naming convention
+        updates.
+
+        """
+
     def column_reflect(self, inspector, table, column_info):
         """Called for each unit of 'column info' retrieved when
         a :class:`_schema.Table` is being reflected.
diff --git a/lib/sqlalchemy/sql/naming.py b/lib/sqlalchemy/sql/naming.py
index 130ec6875..005c41683 100644
--- a/lib/sqlalchemy/sql/naming.py
+++ b/lib/sqlalchemy/sql/naming.py
@@ -39,12 +39,22 @@ class ConventionDict(object):
     def _key_table_name(self):
         return self.table.name
 
-    def _column_X(self, idx):
+    def _column_X(self, idx, attrname):
         if self._is_fk:
-            fk = self.const.elements[idx]
-            return fk.parent
+            try:
+                fk = self.const.elements[idx]
+            except IndexError:
+                return ""
+            else:
+                return getattr(fk.parent, attrname)
         else:
-            return list(self.const.columns)[idx]
+            cols = list(self.const.columns)
+            try:
+                col = cols[idx]
+            except IndexError:
+                return ""
+            else:
+                return getattr(col, attrname)
 
     def _key_constraint_name(self):
         if isinstance(self._const_name, (type(None), _defer_none_name)):
@@ -61,13 +71,13 @@ class ConventionDict(object):
         # note this method was missing before
         # [ticket:3989], meaning tokens like ``%(column_0_key)s`` weren't
         # working even though documented.
-        return self._column_X(idx).key
+        return self._column_X(idx, "key")
 
     def _key_column_X_name(self, idx):
-        return self._column_X(idx).name
+        return self._column_X(idx, "name")
 
     def _key_column_X_label(self, idx):
-        return self._column_X(idx)._ddl_label
+        return self._column_X(idx, "_ddl_label")
 
     def _key_referred_table_name(self):
         fk = self.const.elements[0]
@@ -161,10 +171,28 @@ def _constraint_name_for_table(const, table):
         return None
 
 
+@event.listens_for(
+    PrimaryKeyConstraint, "_sa_event_column_added_to_pk_constraint"
+)
+def _column_added_to_pk_constraint(pk_constraint, col):
+    if pk_constraint._implicit_generated:
+        # only operate upon the "implicit" pk constraint for now,
+        # as we have to force the name to None to reset it.  the
+        # "implicit" constraint will only have a naming convention name
+        # if at all.
+        table = pk_constraint.table
+        pk_constraint.name = None
+        newname = _constraint_name_for_table(pk_constraint, table)
+        if newname:
+            pk_constraint.name = newname
+
+
 @event.listens_for(Constraint, "after_parent_attach")
 @event.listens_for(Index, "after_parent_attach")
 def _constraint_name(const, table):
     if isinstance(table, Column):
+        # this path occurs for a CheckConstraint linked to a Column
+
         # for column-attached constraint, set another event
         # to link the column attached to the table as this constraint
         # associated with the table.
@@ -173,10 +201,11 @@ def _constraint_name(const, table):
             "after_parent_attach",
             lambda col, table: _constraint_name(const, table),
         )
+
     elif isinstance(table, Table):
         if isinstance(const.name, (conv, _defer_name)):
             return
 
         newname = _constraint_name_for_table(const, table)
-        if newname is not None:
+        if newname:
             const.name = newname
diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index 34bedbc6a..127b12e81 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -1777,6 +1777,8 @@ class Column(DialectKWArgs, SchemaItem, ColumnClause):
 
         table._columns.replace(self)
 
+        self.table = table
+
         if self.primary_key:
             table.primary_key._replace(self)
         elif self.key in table.primary_key:
@@ -1786,8 +1788,6 @@ class Column(DialectKWArgs, SchemaItem, ColumnClause):
                 % (self.key, table.fullname)
             )
 
-        self.table = table
-
         if self.index:
             if isinstance(self.index, util.string_types):
                 raise exc.ArgumentError(
@@ -3838,7 +3838,6 @@ class PrimaryKeyConstraint(ColumnCollectionConstraint):
         are already present.
 
         """
-
         # set the primary key flag on new columns.
         # note any existing PK cols on the table also have their
         # flag still set.
@@ -3854,6 +3853,8 @@ class PrimaryKeyConstraint(ColumnCollectionConstraint):
         PrimaryKeyConstraint._autoincrement_column._reset(self)
         self.columns.replace(col)
 
+        self.dispatch._sa_event_column_added_to_pk_constraint(self, col)
+
     @property
     def columns_autoinc_first(self):
         autoinc = self._autoincrement_column