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copied!<h1>Django</h1> <p><a href="https://docs.djangoproject.com/en/dev/ref/models/querysets/#update-or-create" rel="nofollow"><strong>update_or_create</strong></a> (from Django official documentation)</p> <pre><code>update_or_create(defaults=None, **kwargs) </code></pre> <p><em>New in Django 1.7 version.</em></p> <p>A convenience method for updating an object with the given <code>kwargs</code>, creating a new one if necessary. The <code>defaults</code> is a dictionary of (field, value) pairs used to update the object.</p> <p>Returns a tuple of <code>(object, created)</code>, where <code>object</code> is the created or updated object and <code>created</code> is a boolean specifying whether a new object was created.</p> <p>The <code>update_or_create</code> method tries to fetch an object from database based on the given <code>kwargs</code>. If a match is found, it updates the fields passed in the <code>defaults</code> dictionary.</p> <p>This is meant as a shortcut to boilerplatish code. For example:</p> <pre><code>try: obj = Person.objects.get(first_name='John', last_name='Lennon') for key, value in updated_values.iteritems(): setattr(obj, key, value) obj.save() except Person.DoesNotExist: updated_values.update({'first_name': 'John', 'last_name': 'Lennon'}) obj = Person(**updated_values) obj.save() </code></pre> <p>This pattern gets quite unwieldy as the number of fields in a model goes up. The above example can be rewritten using <code>update_or_create()</code> like so:</p> <pre><code>obj, created = Person.objects.update_or_create( first_name='John', last_name='Lennon', defaults=updated_values) </code></pre> <p>For detailed description how names passed in kwargs are resolved see <a href="https://docs.djangoproject.com/en/dev/ref/models/querysets/#django.db.models.query.QuerySet.get_or_create" rel="nofollow"><code>get_or_create()</code></a>.</p> <p>As described above in <a href="https://docs.djangoproject.com/en/dev/ref/models/querysets/#django.db.models.query.QuerySet.get_or_create" rel="nofollow"><code>get_or_create()</code></a>, this method is prone to a race-condition which can result in multiple rows being inserted simultaneously if uniqueness is not enforced at the database level.</p> <h1>AppEngine</h1> <p>Not so lucky yet, as Matt has mentioned earlier, it may not be a common use case. Perhaps in AppEngine it's not so much of such use case. </p>

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