Add new "all columns" naming convention tokens

Added new naming convention tokens ``column_0N_name``, ``column_0_N_name``,
etc., which will render the names / keys / labels for all columns referenced
by a particular constraint in a sequence.  In order to accommodate for the
length of such a naming convention, the SQL compiler's auto-truncation
feature now applies itself to constraint names as well, which creates a
shortened, deterministically generated name for the constraint that will
apply to a target backend without going over the character limit of that
backend.

Additional notes:

1. the SQLite dialect had a format_index method that was apparently not
used, removed.

2. the naming convention logic has been applying the foreign key
remote column spec to the naming convention, and not the actual
column name.  In the case where the referenced Table object uses
.key inside the columns and these are what ForeignKey() references,
the naming convention was doing the wrong thing.   The patch here
fixes this, however this isn't noted in the migration notes.

Fixes: #3989
Change-Id: Ib24f4754b886676096c480fc54b2e5c2463ac99a

1 files changed, 26 insertions, 16 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 27ee4afc6..459e0ba2c 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -2621,17 +2621,7 @@ class DDLCompiler(Compiled):
         else:
             schema_name = None
 
-        ident = index.name
-        if isinstance(ident, elements._truncated_label):
-            max_ = self.dialect.max_index_name_length or \
-                self.dialect.max_identifier_length
-            if len(ident) > max_:
-                ident = ident[0:max_ - 8] + \
-                    "_" + util.md5_hex(ident)[-4:]
-        else:
-            self.dialect.validate_identifier(ident)
-
-        index_name = self.preparer.quote(ident)
+        index_name = self.preparer.format_index(index)
 
         if schema_name:
             index_name = schema_name + "." + index_name
@@ -3162,11 +3152,31 @@ class IdentifierPreparer(object):
         if isinstance(constraint.name, elements._defer_name):
             name = naming._constraint_name_for_table(
                 constraint, constraint.table)
-            if name:
-                return self.quote(name)
-            elif isinstance(constraint.name, elements._defer_none_name):
-                return None
-        return self.quote(constraint.name)
+
+            if name is None:
+                if isinstance(constraint.name, elements._defer_none_name):
+                    return None
+                else:
+                    name = constraint.name
+        else:
+            name = constraint.name
+
+        if isinstance(name, elements._truncated_label):
+            if constraint.__visit_name__ == 'index':
+                max_ = self.dialect.max_index_name_length or \
+                    self.dialect.max_identifier_length
+            else:
+                max_ = self.dialect.max_identifier_length
+            if len(name) > max_:
+                name = name[0:max_ - 8] + \
+                    "_" + util.md5_hex(name)[-4:]
+        else:
+            self.dialect.validate_identifier(name)
+
+        return self.quote(name)
+
+    def format_index(self, index):
+        return self.format_constraint(index)
 
     def format_table(self, table, use_schema=True, name=None):
         """Prepare a quoted table and schema name."""