From 27bb553ba0cf026a811a4c28adc7e97d6339f95c Mon Sep 17 00:00:00 2001
From: Jacob Kaplan-Moss <jacob@jacobian.org>
Date: Thu, 2 Mar 2006 00:28:40 +0000
Subject: [PATCH] Added introspection.table_exists() method to db
 instrospection; this is used all over the place in django.db.management and
 will break under database backends that don't support LIMIT.

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2461 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/db/backends/ado_mssql/introspection.py  |  3 +++
 django/db/backends/dummy/introspection.py      |  1 +
 django/db/backends/mysql/introspection.py      | 13 ++++++++++++-
 django/db/backends/postgresql/introspection.py | 11 +++++++++++
 django/db/backends/sqlite3/introspection.py    | 11 +++++++++++
 5 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/django/db/backends/ado_mssql/introspection.py b/django/db/backends/ado_mssql/introspection.py
index b125cc995f..06755ac2ae 100644
--- a/django/db/backends/ado_mssql/introspection.py
+++ b/django/db/backends/ado_mssql/introspection.py
@@ -10,4 +10,7 @@ def get_relations(cursor, table_name):
 def get_indexes(cursor, table_name):
     raise NotImplementedError
 
+def table_exists(cursor, table_name):
+    raise NotImplementedError
+
 DATA_TYPES_REVERSE = {}
diff --git a/django/db/backends/dummy/introspection.py b/django/db/backends/dummy/introspection.py
index c52a812046..f8cc48b23b 100644
--- a/django/db/backends/dummy/introspection.py
+++ b/django/db/backends/dummy/introspection.py
@@ -4,5 +4,6 @@ get_table_list = complain
 get_table_description = complain
 get_relations = complain
 get_indexes = complain
+table_exists = complain
 
 DATA_TYPES_REVERSE = {}
diff --git a/django/db/backends/mysql/introspection.py b/django/db/backends/mysql/introspection.py
index b4389e6030..c18f944d3d 100644
--- a/django/db/backends/mysql/introspection.py
+++ b/django/db/backends/mysql/introspection.py
@@ -1,3 +1,4 @@
+from django.db import transaction
 from django.db.backends.mysql.base import quote_name
 from MySQLdb.constants import FIELD_TYPE
 
@@ -26,7 +27,17 @@ def get_indexes(cursor, table_name):
     for row in cursor.fetchall():
         indexes[row[4]] = {'primary_key': (row[2] == 'PRIMARY'), 'unique': not bool(row[1])}
     return indexes
-
+    
+def table_exists(cursor, table_name):
+    """Returns True if the given table exists."""
+    try:
+        cursor.execute("SELECT 1 FROM %s LIMIT 1" % quote_name(table_name))
+    except:
+        transaction.rollback_unless_managed()
+        return False
+    else:
+        return True
+        
 DATA_TYPES_REVERSE = {
     FIELD_TYPE.BLOB: 'TextField',
     FIELD_TYPE.CHAR: 'CharField',
diff --git a/django/db/backends/postgresql/introspection.py b/django/db/backends/postgresql/introspection.py
index 63893bd15b..99d74e7f40 100644
--- a/django/db/backends/postgresql/introspection.py
+++ b/django/db/backends/postgresql/introspection.py
@@ -1,3 +1,4 @@
+from django.db import transaction
 from django.db.backends.postgresql.base import quote_name
 
 def get_table_list(cursor):
@@ -66,6 +67,16 @@ def get_indexes(cursor, table_name):
         col_name = desc[int(row[0])-1][0]
         indexes[col_name] = {'primary_key': row[2], 'unique': row[1]}
     return indexes
+    
+def table_exists(cursor, table_name):
+    """Returns True if the given table exists."""
+    try:
+        cursor.execute("SELECT 1 FROM %s LIMIT 1" % quote_name(table_name))
+    except:
+        transaction.rollback_unless_managed()
+        return False
+    else:
+        return True
 
 # Maps type codes to Django Field types.
 DATA_TYPES_REVERSE = {
diff --git a/django/db/backends/sqlite3/introspection.py b/django/db/backends/sqlite3/introspection.py
index 0ca971c0d4..413e4b958e 100644
--- a/django/db/backends/sqlite3/introspection.py
+++ b/django/db/backends/sqlite3/introspection.py
@@ -1,3 +1,4 @@
+from django.db import transaction
 from django.db.backends.sqlite3.base import quote_name
 
 def get_table_list(cursor):
@@ -14,6 +15,16 @@ def get_relations(cursor, table_name):
 def get_indexes(cursor, table_name):
     raise NotImplementedError
 
+def table_exists(cursor, table_name):
+    """Returns True if the given table exists."""
+    try:
+        cursor.execute("SELECT 1 FROM %s LIMIT 1" % quote_name(table_name))
+    except:
+        transaction.rollback_unless_managed()
+        return False
+    else:
+        return True
+
 # Maps SQL types to Django Field types. Some of the SQL types have multiple
 # entries here because SQLite allows for anything and doesn't normalize the
 # field type; it uses whatever was given.