Question

I want to automatically add some items to a model’s ManyToMany field when it is saved in the Django admin UI. However, calling model.many2manyfield.add() is failing silently

my django app’s models.py

...
class Dashboard(models.Model):
    name = models.TextField()
    url = models.TextField()
    graphs = models.ManyToManyField(Graph, null=True, blank=True)

my django app’s admin.py

from models import Dashboard
...
class DashboardAdmin(GraphAdmin):
    def save_model(self, request, dashboard, form, change):
        dashboard.save()
        graphite_util.sync_dashboard_graphs(dashboard)

...
admin.site.register(Dashboard, DashboardAdmin)

from graphite_util.py:

def sync_dashboard_graphs(dashboard):
    print "Syncing %s " % dashboard

    ...
            graph = None
            try:
                graph = Graph.objects.get(url=url)
            except Graph.DoesNotExist:
                graph = Graph()
                graph.url = url
                graph.save()
            print "adding graph %s to dashboard %s" %(graph, dashboard)
            dashboard.graphs.add(graph) #TODO: why does this fail silently?

Is what I want to do somehow illegal? If so, are there other options?

Thanks!

Answer 1

In principle it should work; however, you’ve got some inconsistencies in your code. For example, you’re looking up the graph based on url. You’ve redacted part of your code, so it’s possible you created the variable in the missing part, but I’m not sure where you would have gotten that info from; you have no access to the request from this method.

However, you could pass the request in to the method from where it’s called in save_model because the request is available there.

Additionally, if you’re simply going to create a graph in the except block, you’re better off using get_or_create.

graph = Graph.objects.get_or_create(url=url)

It basically does the same thing, but much more concisely.