helpers

helpers Package

database

Mongo Engine interaction utilities.

qirest_client.helpers.database.get_or_create(klass, key, **non_key)

This function stands in for the Mongo Engine get_or_create collection method which was deprecated in mongoengine v0.8.0 and dropped in mongoengine v0.10.0, since MongoDB does not support transactions.

If there is an object of the given Mongo Engine data model class which matches the given secondary key, then that object is returned. Otherwise, a new object is created with the content prescribed by both the primary and non-primary parameters.

The create step is an upsert, i.e. a new object is created if and only if it does not yet exist. The upsert allows for the small possibility that an object is created after the fetch attempt but before the create attempt. In that situation, the existing object non-key content is modified and the modified object is returned.

Note:

The idiom used in this function modifies the solution proposed in http://stackoverflow.com/questions/25846462/mongoengine-replacing-get-or-create-with-upsert-update-one/25863633#25863633. That StackOverflow work-around returns the following error:

ValueError: update only works with $ operators

The work-around to the StackOverflow work-around is to call the data model class update_one method rather than modify.

Parameters:

• klass – the Mongo Engine data model class
• key – the secondary key {attribute: value} dictionary
• non_key – the non-key {attribute: value} dictionary

Returns:

the existing or new object