When a record returns the IDs of records in a hasMany relationship, Ember Data allows us to opt-in to combine these requests into a single request.
Note: Using hyperlinked related fields to retrieve related records in a single request is preferred over using coalesceFindRequests since there is a limit on the number of records per request on read-only fields due to URL length restrictions.
Suppose you have Ember models:
// app/models/person.js
import DS from 'ember-data';
export default DS.Model.extend({
name: DS.attr('string'),
pets: DS.hasMany('pet', { async: True })
});
// app/models/pet.js
import DS from 'ember-data';
export default DS.Model.extend({
age: DS.attr('number')
});
An out-of-the-box DRF model serializer for Person would return something like this:
GET /api/people/1/
{
"id": 1,
"name": "Fred",
"pets": [1, 2, 3]
}
When Ember Data decides to resolve the pets, by default it would fire 3 separate requests. In this case:
GET /api/pets/1/
{
"id": 1,
"age": 5
}
GET /api/pets/2/
{
"id": 2,
"age": 5
}
GET /api/pets/3/
{
"id": 3,
"age": 6
}
However, if we opt-in to coalesceFindRequests, we can consolidate this into 1 call.
Extend the adapter, and enable coalesceFindRequests:
// app/adapters/application.js
import DRFAdapter from './drf';
export default DRFAdapter.extend({
coalesceFindRequests: true
});
Now, when Ember Data resolves the pets, it will fire a request that looks like this:
GET /api/pets/?ids[]=1&ids[]=2&ids[]=3
All this is great, except Django REST Framework is not quite able to handle such a request out of the box. Thankfully, DRF allows you to plug in custom filters, and writing a filter for this kind of request is super simple.
In your project somewhere, write the following filter:
# myapp/filters.py
from rest_framework import filters
class CoalesceFilterBackend(filters.BaseFilterBackend):
"""
Support Ember Data coalesceFindRequests.
"""
def filter_queryset(self, request, queryset, view):
id_list = request.query_params.getlist('ids[]')
if id_list:
# Disable pagination, so all records can load.
view.pagination_class = None
queryset = queryset.filter(id__in=id_list)
return queryset
Now you just need to add this filter to filter_backends in your views, e.g.:
from myapp.filters import CoalesceFilterBackend
class UserListView(generics.ListAPIView):
queryset = User.objects.all()
serializer = UserSerializer
filter_backends = (CoalesceFilterBackend,)
Or, configure it globally in your DRF settings:
REST_FRAMEWORK = {
'DEFAULT_FILTER_BACKENDS': ('myapp.filters.CoalesceFilterBackend',)
}
Now, when Ember Data sends the coalesced request, DRF will return meaningful data:
GET /api/pets/?ids[]=1&ids[]=2&ids[]=3
[
{
"id": 1,
"age": 5
},
{
"id": 2,
"age": 5
},
{
"id": 3,
"age": 6
}
]