Use separate label generator for column_label naming convention

Fixed bug where a table that would have a column label overlap with a plain
column name, such as "foo.id AS foo_id" vs. "foo.foo_id", would prematurely
generate the ``._label`` attribute for a column before this overlap could
be detected due to the use of the ``index=True`` or ``unique=True`` flag on
the column in conjunction with the default naming convention of
``"column_0_label"``.  This would then lead to failures when ``._label``
were used later to generate a bound parameter name, in particular those
used by the ORM when generating the WHERE clause for an UPDATE statement.
The issue has been fixed by using an alternate ``._label`` accessor for DDL
generation that does not affect the state of the :class:`.Column`.   The
accessor also bypasses the key-deduplication step as it is not necessary
for DDL, the naming is now consistently ``"<tablename>_<columnname>"``
without any subsequent numeric symbols when used in DDL.

Fixes: #4911

Change-Id: Iabf5fd3250738d800d6e41a2a3a27a7ce2405e7d

4 files changed, 39 insertions, 19 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index c6c30629d..5ecec7d6c 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -3022,6 +3022,10 @@ class DDLCompiler(Compiled):
         text = "CREATE "
         if index.unique:
             text += "UNIQUE "
+        if index.name is None:
+            raise exc.CompileError(
+                "CREATE INDEX requires that the index have a name"
+            )
         text += "INDEX %s ON %s (%s)" % (
             self._prepared_index_name(index, include_schema=include_schema),
             preparer.format_table(
@@ -3038,6 +3042,11 @@ class DDLCompiler(Compiled):
 
     def visit_drop_index(self, drop):
         index = drop.element
+
+        if index.name is None:
+            raise exc.CompileError(
+                "DROP INDEX requires that the index have a name"
+            )
         return "\nDROP INDEX " + self._prepared_index_name(
             index, include_schema=True
         )
@@ -3251,7 +3260,8 @@ class DDLCompiler(Compiled):
         text = ""
         if constraint.name is not None:
             formatted_name = self.preparer.format_constraint(constraint)
-            text += "CONSTRAINT %s " % formatted_name
+            if formatted_name is not None:
+                text += "CONSTRAINT %s " % formatted_name
         text += "UNIQUE (%s)" % (
             ", ".join(self.preparer.quote(c.name) for c in constraint)
         )
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index b6462b334..78c434cff 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -4263,7 +4263,11 @@ class ColumnClause(roles.LabeledColumnExprRole, Immutable, ColumnElement):
     def _render_label_in_columns_clause(self):
         return self.table is not None
 
-    def _gen_label(self, name):
+    @property
+    def _ddl_label(self):
+        return self._gen_label(self.name, dedupe_on_key=False)
+
+    def _gen_label(self, name, dedupe_on_key=True):
         t = self.table
 
         if self.is_literal:
@@ -4287,21 +4291,22 @@ class ColumnClause(roles.LabeledColumnExprRole, Immutable, ColumnElement):
                 assert not isinstance(label, quoted_name)
                 label = quoted_name(label, t.name.quote)
 
-            # ensure the label name doesn't conflict with that
-            # of an existing column.   note that this implies that any
-            # Column must **not** set up its _label before its parent table
-            # has all of its other Column objects set up.  There are several
-            # tables in the test suite which will fail otherwise; example:
-            # table "owner" has columns "name" and "owner_name".  Therefore
-            # column owner.name cannot use the label "owner_name", it has
-            # to be "owner_name_1".
-            if label in t.c:
-                _label = label
-                counter = 1
-                while _label in t.c:
-                    _label = label + "_" + str(counter)
-                    counter += 1
-                label = _label
+            if dedupe_on_key:
+                # ensure the label name doesn't conflict with that of an
+                # existing column.   note that this implies that any Column
+                # must **not** set up its _label before its parent table has
+                # all of its other Column objects set up.  There are several
+                # tables in the test suite which will fail otherwise; example:
+                # table "owner" has columns "name" and "owner_name".  Therefore
+                # column owner.name cannot use the label "owner_name", it has
+                # to be "owner_name_1".
+                if label in t.c:
+                    _label = label
+                    counter = 1
+                    while _label in t.c:
+                        _label = label + "_" + str(counter)
+                        counter += 1
+                    label = _label
 
             return coercions.expect(roles.TruncatedLabelRole, label)
 
diff --git a/lib/sqlalchemy/sql/naming.py b/lib/sqlalchemy/sql/naming.py
index 68a6190cf..3fca4e35b 100644
--- a/lib/sqlalchemy/sql/naming.py
+++ b/lib/sqlalchemy/sql/naming.py
@@ -67,7 +67,7 @@ class ConventionDict(object):
         return self._column_X(idx).name
 
     def _key_column_X_label(self, idx):
-        return self._column_X(idx)._label
+        return self._column_X(idx)._ddl_label
 
     def _key_referred_table_name(self):
         fk = self.const.elements[0]
diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index af538af0e..4e8f4a397 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -1434,7 +1434,12 @@ class Column(DialectKWArgs, SchemaItem, ColumnClause):
                     "To create indexes with a specific name, create an "
                     "explicit Index object external to the Table."
                 )
-            Index(None, self, unique=bool(self.unique), _column_flag=True)
+            table.append_constraint(
+                Index(
+                    None, self.key, unique=bool(self.unique), _column_flag=True
+                )
+            )
+
         elif self.unique:
             if isinstance(self.unique, util.string_types):
                 raise exc.ArgumentError(