magic-removal: Fixed #1483 -- Added MySQL foreign-key inspection to 'inspectdb'. Thanks, mir@noris.de

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2691 bcc190cf-cafb-0310-a4f2-bffc1f526a37

AUTHORS

@@ -80,6 +80,7 @@ answer newbie questions, and generally made Django that much better:
     mattycakes@gmail.com
     Jason McBrayer <http://www.carcosa.net/jason/>
     michael.mcewan@gmail.com
+    mir@noris.de
     mmarshall
     Eric Moritz <http://eric.themoritzfamily.com/>
     Robin Munn <http://www.geekforgod.com/>

django/db/backends/mysql/introspection.py

@@ -1,6 +1,10 @@
 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."
@@ -12,8 +16,49 @@ def get_table_description(cursor, table_name):
     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())
+
+    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):
     """