Fixed django#5725 -- Fixed varchar column size introspection for MySQL

Thanks ferdonline for the initial patch and Karen Tracey for the related post on django-users.

Author: claudep

django/db/backends/mysql/introspection.py

@@ -36,9 +36,20 @@ def get_table_list(self, cursor):
  return [row[0] for row in cursor.fetchall()]
 
  def get_table_description(self, cursor, table_name):
- "Returns a description of the table, with the DB-API cursor.description interface."
+ """
+ Returns a description of the table, with the DB-API cursor.description interface."
+ """
+ # varchar length returned by cursor.description is an internal length,
+ # not visible length (#5725), use information_schema database to fix this
+ cursor.execute("""
+ SELECT column_name, character_maximum_length FROM information_schema.columns
+ WHERE table_name = %s AND table_schema = DATABASE()
+ AND character_maximum_length IS NOT NULL""", [table_name])
+ length_map = dict(cursor.fetchall())
+
  cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
- return cursor.description
+ return [line[:3] + (length_map.get(line[0], line[3]),) + line[4:]
+ for line in cursor.description]
 
  def _name_to_index(self, cursor, table_name):
  """

tests/regressiontests/introspection/tests.py

@@ -89,6 +89,11 @@ def test_get_table_description_types(self):
  [datatype(r[1], r) for r in desc],
  ['IntegerField', 'CharField', 'CharField', 'CharField', 'BigIntegerField']
  )
+ # Check also length of CharFields
+ self.assertEqual(
+ [r[3] for r in desc if datatype(r[1], r) == 'CharField'],
+ [30, 30, 75]
+ )
 
  # Oracle forces null=True under the hood in some cases (see
  # https://docs.djangoproject.com/en/dev/ref/databases/#null-and-empty-strings)