Nested transactions

src/transaction.rs

@@ -181,6 +181,21 @@ pub trait WriteTransaction<'env> : ReadTransaction<'env> {
                                              .unwrap_or(ptr::null_mut())))
         }
     }
+
+    /// Begins a new nested transaction inside of this transaction.
+    fn begin_nested_txn<'txn>(&'txn mut self) -> LmdbResult<RwTransaction<'txn>> {
+        let mut nested: *mut ffi::MDB_txn = ptr::null_mut();
+        unsafe {
+            let env: *mut ffi::MDB_env = ffi::mdb_txn_env(self.txn());
+            ffi::mdb_txn_begin(env, self.txn(), 0, &mut nested);
+        }
+        Ok(RwTransaction {
+            txn: nested,
+            _no_sync: marker::NoSync,
+            _no_send: marker::NoSend,
+            _contravariant: marker::ContravariantLifetime::<'env>,
+        })
+    }
 }
 
 /// An LMDB read-only transaction.
@@ -427,6 +442,26 @@ mod test {
         assert!(active.get(db, b"key").is_ok());
     }
 
+    #[test]
+    fn test_nested_txn() {
+        let dir = io::TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path(), io::USER_RWX).unwrap();
+        let db = env.open_db(None).unwrap();
+
+        let mut txn = env.begin_write_txn().unwrap();
+        txn.put(db, b"key1", b"val1", WriteFlags::empty()).unwrap();
+
+        {
+            let mut nested = txn.begin_nested_txn().unwrap();
+            nested.put(db, b"key2", b"val2", WriteFlags::empty()).unwrap();
+            assert_eq!(nested.get(db, b"key1").unwrap(), Some(b"val1"));
+            assert_eq!(nested.get(db, b"key2").unwrap(), Some(b"val2"));
+        }
+
+        assert_eq!(txn.get(db, b"key1").unwrap(), Some(b"val1"));
+        assert_eq!(txn.get(db, b"key2").unwrap(), None);
+    }
+
     #[test]
     fn test_concurrent_readers_single_writer() {
         let dir = io::TempDir::new("test").unwrap();