MongoDB AppEngine Connector

Info

See the mongodb site for more information. See github for the latest source.

Author

Mike Dirolf <mike@10gen.com>

About

The MongoDB AppEngine Connector provides a drop-in replacement for App Engine's datastore API, using MongoDB as a backend.

Questions and Support

Questions about the MongoDB AppEngine Connector should be directed to the mongodb-user group.

Usage

The following steps can be used to get Google AppEngine working with MongoDB:

Install MongoDB

Instructions for installing MongoDB on your platform can be found on the mongodb site.

After installing, start an instance of mongod on the default port:

$ mongod run

Get the Google AppEngine Code

In order to use the connector, you must patch the AppEngine source distribution, which can be found here and checked out via:

$ svn checkout http://googleappengine.googlecode.com/svn/trunk/ googleappengine-read-only

Be sure that you meet all the pre-requisites listed in the README in the resulting directory.

Patch the AppEngine Code

This adapter has been tested against revision 77 from Google AppEngine's svn repository. To find the revision number of the repository that you checked out, go into the root of the repository and type:

$ svn info

To apply the patch, do the following from a command line:

$ cd googleappengine-read-only
$ cd python/ # need to do this if you checked out all the different AE languages
$ patch -p0 < gae_patch.diff

you should see output similar to:

patching file dev_appserver.py
patching file google/appengine/tools/dev_appserver.py

If you see no error messages, your patching was successful.

Set the MongoDB Connector Directory

In the AppEngine distribution, we patched dev_appserver.py in the previous step, and now we need to edit it by hand. Open the file in your favorite editor, and look for the line:

"PATH/TO/MONGO-APPENGINE-CONNECTOR/DIRECTORY"

and change it to the appropriate value. Remember to keep the double quotes.

Install PyMongo, the Python Driver for MongoDB

If you've already installed the MongoDB python driver - PyMongo - you can skip this step.

To install PyMongo:

$ easy_install pymongo

Run the Tests

Once AppEngine is patched, pymongo is installed, and MongoDB is up and running, you can test the installation by running the adapter's unit tests.

To do so, simply start AE via the SDK's start script dev_appserver.py with the full path to the test/test_site directory in the adapter distribution. So, starting in the root of the AppEngine SDK:

$ ./dev_appserver.py /my/path/to/mongodb-appengine-connector/test/test_site

Then, if you direct your browser to http://localhost:8080 you should see a single test page that begins with:

Datastore API
Test a simple db example...
Test that ids get incremented properly between sessions...
Slightly less simple db test...
Test db exceptions...
Test a delete...
Test a delete on an unsaved object...
...

As long as you don't see the word FAIL all tests have passed.

Other Notes

• Right now, the Connection cannot be configured. It attempts to connect to a standalone MongoDB instance on localhost:27017.
• Transactions are unsupported. When any operation requiring transactions is performed a warning will be logged and the operation will be performed transaction-less.
• DateTime values get rounded to the nearest millisecond when saved to MongoDB. This is a limitation of MongoDB's date representation, and is not specific to this adaptor.
• In order to actually create indexes the dev_appserver must be run with the --require-indexes option. Running with this option will probably add significant overhead, since each time the dev_appserver checks to see if it should create an index a query is performed.
• Index creation ignores the "Ancestor" option. This option would just create an index on '_id', which MongoDB creates automatically anyway.

Authors

• Mike Dirolf (mdirolf)
  • Original implementation
• Tobias Rodabel (Tobias)
  • Fixes and maintenance for newer versions of AppEngine