How to get reverse related objects using Schema?

[EMUNES]

It's pretty convenient to return objects with nested foreign-key objects using ninja. However, I find no tutorial to return objects including reverse related objects using ninja.

Say I have a Django PostComment model whose foreign-key field points to Post object. And for API I want to return a list of Post objects each includes all comments that points to it. Is it possible to do so using Schemas and if so how should I customize the api code?

I'm new to ninja, Thanks for any hint :)

[vitalik]

Hi @EMUNES

Try the folloing:

from typing import List
from ninja import Schema, Field

class CommentSchema(Schema):
    # define your comment attrs here:
    id: int
    message: str

class PostSchema(Schema):
    id: str
    title: str
    comments: List[CommentSchema] = Field(..., alias='postcomment_set')  # postcomment_set is based on your model or related attr



@api.get('/posts', response=List[PostSchema])
def list_posts(reqiest):
     return Post.objects.all() 

[rngallen]

Hello I want to use pre_fetch_related and select_related to reduce number of database queries
My schema are as follows

class OrderOutSchema(Schema):
    id: int
    customer: CustomerOrderSchema
    order_number: str
    order_date: date
    reference: str
    product: ProductOrderSchema
    vessel: VesselOrderSchema
    quantity: Decimal
    trucks: int
    created: datetime
    updated: datetime
    created_by: CreatedByOrderSchema
    order_lines: List[OrderLineOutSchema]

class OrderLineOutSchema(Schema):
    id: int
    order_id: int
    line: int
    driver: DriverOrderLineSchema
    truck: TruckOrderLineSchema
    loading_date: date

my query is

    qs = Order.objects.all().select_related("customer", "product", "vessel", "created_by").prefetch_related("order_lines") 
    if order_number:
        qs = qs.filter(Q(order_number__icontains=order_number))
    offset = (page - 1) * per_page
    qs = qs[offset : offset + per_page]
    return HTTPStatus.OK, qs

but how can I use select _related on OrderLineOutSchema for driver(DriverOrderLineSchema) and truck(TruckOrderLineSchema)??? Other wise for every line on I should query Truck Model and Driver Model respectively.

[EMUNES]

Thanks a lot. I didn't expect that I can get reverse objects simply by declaring them in Schema. This is really convenient. I will definitely try this in my future project.

[jet10000]

Please add it to document

[quroom]

I think so.

[mohanish2504]

Does nested objects support support async?

[MiltosD]

I tried comments: List[CommentSchema] = Field(..., alias='postcomment_set') and got

Input should be a valid list [type=list_type, input_value=<django.db.models.fields....bject at 0x7f3d69345110>, input_type=create_reverse_many_to_one_manager.<locals>.RelatedManager]

[vitalik]

@MiltosD need to see more of your code