Custom Query with NestedField not behaving as expected

[bailey-heit]

Let's say we have 2 tables and a many_to_many table: \

product

| id | name | ...  | 
_________________________
| 4 | paper | ... | 
| 5 | string | ... | 
| 6 | water | ... | 
| 7 | paint |  ... | 

customer

| id | name | ... | 
_________________________
| 11 | bobby | ... | 
| 12 | sally | ... | 
| 13 | billy | ... | 
| 14 | joel |  ... | 

product_2_customer

id | c_id | p_id|
_________________________
108 | 4 | 11 | 
109 | 4 | 12 |
117 | 5 | 13 | 
119 | 6 | 13 | 
120 | 7 | 13 | 

Our Product Serializer looks something like:

class ProductSerializer(NestedModelSerializer):
        ... 
        customers = NestedField(CustomerSerializer, required=False, many=True, create_ops=["add"], update_ops=["add", "remove"])

Our Customer Model looks something like:

class Product():
         name = models.CharField(max_length=128)
         ...
         customers = models.ManyToManyField('Person', through="TreatmentRun2Person", blank=True)

When we run a default query on products, we get the expected results. For example, the customer object with id=13 associated with product id=5 is correctly returned.

 { 
...
    "customers": [
                {
                    "id": 13,
                    "first_name": "billy",
                    "last_name": "jean"
                }
            ],
...
}

However, when we run a custom query, ie /api/products/?&query={attributes,created_at,persons{id,first_name,last_name},suppliers{id,name}} then for product 5, the customer object returned is 13 repeated 3 times (for each time it's associated with a product). Better demonstrated:

 { 
...
    "customers": [
                {
                    "id": 13,
                    "first_name": "billy",
                    "last_name": "jean"
                },
                {
                    "id": 13,
                    "first_name": "billy",
                    "last_name": "jean"
                },
               {
                    "id": 13,
                    "first_name": "billy",
                    "last_name": "jean"
                }
            ],
...
}

This is not the behavior we would expect and we were wondering why the behavior changes when the query filter is applied? Thank you.