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cookbook/trasactions.md

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+---
+layout: default
+title: How to use database transactions
+---
+
+# How to use database transactions
+
+### Problem
+
+How to use database transactions
+
+
+### Solution
+
+The web.DB class has a method `transaction` which returns a transaction object. The transaction object can be used to commit or rollback a transaction.
+
+    import web
+
+    db = web.databse(dbn="postgres", db="webpy", user="foo", pw="")
+    t = db.transaction()
+    try:
+        db.insert('person', name='foo')
+        db.insert('person', name='bar')
+    except:
+        t.rollback()
+        raise
+    else:
+        t.commit()
+
+With python 2.5+, transaction can be used as with statement also.
+
+    db = web.databse(dbn="postgres", db="webpy", user="foo", pw="")
+     
+    with db.transaction():
+        db.insert('person', name='foo')
+        db.insert('person', name='bar')
+        
+
+It is also possible to have nested transactions.
+
+    def post(title, body, tags):
+        t = db.transaction()
+        try:
+            post_id = db.insert('post', title=title, body=body)
+            add_tags(post_id, tags)
+        except:
+            t.rollback()
+        else:
+            t.commit()
+
+    def add_tags(post_id, tags):
+        t = db.transaction()
+        try:
+            for tag in tags:
+                db.insert('tag', post_id=post_id, tag=tag)
+        except:
+            t.rollback()
+        else:
+            t.commit()
+
+
+Nested transactions are ignored for sqlite as they are not supported.