Django Tastypie过滤器OR语句

from tastypie.resources import ModelResource
from tastypie import fields
from tastypie.constants import ALL
from django.db.models import Q

from myapp.models import MyModel

class MyModelResource(ModelResource):
    field1 = fields.CharField(attribute='field1')
    field2 = fields.CharField(attribute='field2')

    class Meta:
        queryset = MyModel.objects.all()
        resource_name = 'mymodel'
        filtering = {
            'field1': ALL,
            'field2': ALL,
        }

    def build_filters(self, filters=None):
        if filters is None:
            filters = {}

        orm_filters = super(MyModelResource, self).build_filters(filters)

        if 'q' in filters:
            q = filters['q']
            orm_filters.update({
                'custom_filter': Q(field1__icontains=q) | Q(field2__icontains=q),
            })

        return orm_filters

GET /api/mymodel/?format=json&q=search_term