Django Array contains a field

Question

I am using Django, with mongoengine. I have a model Classes with an inscriptions list, And I want to get the docs that have an id in that list.

classes = Classes.objects.filter(inscriptions__contains=request.data['inscription'])

Answer 1

Here's a general explanation of querying ArrayField membership:

Per the Django ArrayField docs, the __contains operator checks if a provided array is a subset of the values in the ArrayField.

So, to filter on whether an ArrayField contains the value "foo", you pass in a length 1 array containing the value you're looking for, like this:

# matches rows where myarrayfield is something like ['foo','bar']
Customer.objects.filter(myarrayfield__contains=['foo'])

The Django ORM produces the @> postgres operator, as you can see by printing the query:

print Customer.objects.filter(myarrayfield__contains=['foo']).only('pk').query
>>> SELECT "website_customer"."id" FROM "website_customer" WHERE "website_customer"."myarrayfield_" @> ['foo']::varchar(100)[]

If you provide something other than an array, you'll get a cryptic error like DataError: malformed array literal: "foo" DETAIL: Array value must start with "{" or dimension information.