Ticket #1483: 1483-clean.diff

django/db/backends/mysql/introspection.py

@@ -1 +1 @@
 from django.db import transaction
 from django.db.backends.mysql.base import quote_name
+from MySQLdb import ProgrammingError, OperationalError
 from MySQLdb.constants import FIELD_TYPE
+import re
 
+foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) REFERENCES `([^`]*)` \(`([^`]*)`\)")
+
 def get_table_list(cursor):
     "Returns a list of table names in the current database."
     cursor.execute("SHOW TABLES")
@@ -12 +16 @@
     cursor.execute("SELECT * FROM %s LIMIT 1" % quote_name(table_name))
     return cursor.description
 
+def _name_to_index(cursor, table_name):
+    """
+    Returns a dictionary of {field_name: field_index} for the given table.
+    Indexes are 0-based.
+    """
+    return dict([(d[0], i) for i, d in enumerate(get_table_description(cursor, table_name))])
+
 def get_relations(cursor, table_name):
-    raise NotImplementedError
+    """
+    Returns a dictionary of {field_index: (field_index_other_table, other_table)}
+    representing all relationships to the given table. Indexes are 0-based.
+    """
+    my_field_dict = _name_to_index(cursor, table_name)
+    constraints = []
+    relations = {}
+    try:
+        # This should work for MySQL 5.0.
+        cursor.execute("""
+            SELECT column_name, referenced_table_name, referenced_column_name
+            FROM information_schema.key_column_usage
+            WHERE table_name = %s
+                AND referenced_table_name IS NOT NULL
+                AND referenced_column_name IS NOT NULL""", [table_name])
+        constraints.extend(cursor.fetchall())
+    except (ProgrammingError, OperationalError):
+        # Fall back to "SHOW CREATE TABLE", for previous MySQL versions.
+        # Go through all constraints and save the equal matches.
+        cursor.execute("SHOW CREATE TABLE %s" % table_name)
+        for row in cursor.fetchall():
+            pos = 0
+            while True:
+                match = foreign_key_re.search(row[1], pos)
+                if match == None:
+                    break
+                pos = match.end()
+                constraints.append(match.groups())
 
+    # handle constraints. (can't do this in the loop above since we need the cursor in both places)
+    for my_fieldname, other_table, other_field in constraints:
+        other_field_index = _name_to_index(cursor, other_table)[other_field]
+        my_field_index = my_field_dict[my_fieldname]
+        relations[my_field_index] = (other_field_index, other_table)
+    return relations
+
 def get_indexes(cursor, table_name):
     """
     Returns a dictionary of fieldname -> infodict for the given table,