various compiler improvements consolidated from multiple commits

Commit information is from https://github.com/avidal/django-pyodbc

2012-06-28 13:44:33 -0500: 6f2dfa3 - Fix bug when generating insert queries on django < 1.4.
2012-06-20 15:13:39 -0500: 6b9ca0a - Use SCOPE_IDENTITY in INSERT queries to get the inserted id.
2012-02-09 11:21:00 -0600: c2bc6de - Fix bug when inserting with a specific primary key.
2012-02-07 10:46:54 -0600: b1ecdc4 - Fixed bug in regards to bulk inserting.
2012-02-03 15:46:11 -0600: c7ca41d - Make it backwards compatible.
2012-02-03 12:48:13 -0600: 0dd232b - Deal with bulk_insert related changes.

Author: avidal

django_pyodbc/compiler.py

@@ -280,23 +280,54 @@ def as_sql(self):
         qn = self.connection.ops.quote_name
         opts = self.query.model._meta
         result = ['INSERT INTO %s' % qn(opts.db_table)]
-        result.append('(%s)' % ', '.join([qn(c) for c in self.query.columns]))
+
+        has_fields = bool(self.query.fields)
+        fields = self.query.fields if has_fields else [opts.pk]
+        columns = [f.column for f in fields]
+
+        result.append('(%s)' % ', '.join([qn(c) for c in columns]))
+
+        if has_fields:
+            params = values = [
+                [
+                    f.get_db_prep_save(getattr(obj, f.attname) if self.query.raw else f.pre_save(obj, True), connection=self.connection)
+                    for f in fields
+                ]
+                for obj in self.query.objs
+            ]
+        else:
+            values = [[self.connection.ops.pk_default_value()] for obj in self.query.objs]
+            params = [[]]
+            fields = [None]
+
+        placeholders = [
+            [self.placeholder(field, v) for field, v in zip(fields, val)]
+            for val in values
+        ]
+
         if self.return_id and self.connection.features.can_return_id_from_insert:
+            params = params[0]
             output = 'OUTPUT inserted.%s' % qn(opts.pk.column)
             result.append(output)
-        values = [self.placeholder(*v) for v in self.query.values]
-        result.append('VALUES (%s)' % ', '.join(values))
-        params = self.query.params
-        sql = ' '.join(result)
+            result.append("VALUES (%s)" % ", ".join(placeholders[0]))
+            return [(" ".join(result), tuple(params))]
+
+        sql, params = [
+            (" ".join(result + ["VALUES (%s)" % ", ".join(p)]), vals)
+            for p, vals in zip(placeholders, params)
+        ]
 
+        # This section deals with specifically setting the primary key,
+        # or using default values if necessary
         meta = self.query.get_meta()
         if meta.has_auto_field:
             # db_column is None if not explicitly specified by model field
             auto_field_column = meta.auto_field.db_column or meta.auto_field.column
 
-            if auto_field_column in self.query.columns:
+            if auto_field_column in columns:
                 quoted_table = self.connection.ops.quote_name(meta.db_table)
-                if len(self.query.columns) == 1 and not params:
+                # If there are no fields specified in the insert..
+                if not has_fields:
                     sql = "INSERT INTO %s DEFAULT VALUES" % quoted_table
                 else:
                     sql = "SET IDENTITY_INSERT %s ON;\n%s;\nSET IDENTITY_INSERT %s OFF" % \