Making models.py for Django Rest Framework Primary key and foreign key

Question

I made a models like this:

from django.db import models
import json

# Create your models here.
class Data(models.Model):
node_id = models.ForeignKey("Node", on_delete=models.CASCADE)
timestamp = models.DateTimeField()
vibration = models.IntegerField()
moisture = models.IntegerField()
gps_latitude = models.CharField(max_length=250)
gps_longitude = models.CharField(max_length=250)
gyro_x = models.FloatField()
gyro_y = models.FloatField()
gyro_z = models.FloatField()
accelero_x = models.FloatField()
accelero_y = models.FloatField()
accelero_z = models.FloatField()
displacement = models.IntegerField()


class Node(models.Model):
node_id = models.IntegerField()
latitude = models.CharField(max_length=250)
longitude = models.CharField(max_length=250)
lokasi = models.CharField(max_length=500)

The Data models have endpoint at http://127.0.0.1:8000/api/data/ And Node models have endpoint at http://127.0.0.1:8000/api/node/ I want the node_id in Node class to become a primary key and the node_id from Data class to become a foreign key. I try to post to http://127.0.0.1:8000/api/node/ like this:

    {
    "node_id": 1,
    "latitude": "123",
    "longitude": "123",
    "lokasi": "eer"
}

And then I open the endpoint for Data models at http://127.0.0.1:8000/api/data/ to post some data. On the Node id field, it should be referring to node_id=1, but why it just referring to node object(8) which is the id that generates automatically from Django rest framework?

It makes the post data look like this:

{
"id": 13,
"timestamp": "2020-04-14T20:00:00+07:00",
"vibration": 1,
"moisture": 1,
"gps_latitude": "123",
"gps_longitude": "123",
"gyro_x": 1.0,
"gyro_y": 1.0,
"gyro_z": 1.0,
"accelero_x": 1.0,
"accelero_y": 1.0,
"accelero_z": 1.0,
"displacement": 1,
"node_id": 8}

The "node_id": should be 1 not 8. Is there any wrong with my models?

Answer 1

Depending on the relation, which I supposed is 1:N (Node:Data)

So if you'd rewrite your models to:

class Node(models.Model):
    latitude = models.CharField(max_length=250)
    longitude = models.CharField(max_length=250)
    lokasi = models.CharField(max_length=500)

    def __str__(self):
        return self.lokasi


class Data(models.Model):
    node_id = models.ForeignKey(Node, related_name="data", on_delete=models.CASCADE)
    timestamp = models.DateTimeField()
    vibration = models.IntegerField()
    moisture = models.IntegerField()
    gps_latitude = models.CharField(max_length=250)
    gps_longitude = models.CharField(max_length=250)
    gyro_x = models.FloatField()
    gyro_y = models.FloatField()
    gyro_z = models.FloatField()
    accelero_x = models.FloatField()
    accelero_y = models.FloatField()
    accelero_z = models.FloatField()
    displacement = models.IntegerField()

So now you can assign Node by id when creating Data model, and vice versa you can assign collection of data objects from Node by calling

Node.objects.first().data.all()

Ad: why it just referring to node object(8)

You need to add a __str__ method which will tell Django how to interpret your object when casted to string, so I added a example into your Node class

Node will have id field as Autogenerated Primary key and node_id as ForeignKey to Node

Answer 2

Since you are trying to design the back end for a GPS system, I would recommend checking https://github.com/openwisp/django-rest-framework-gis &https://docs.djangoproject.com/en/dev/ref/contrib/gis/tutorial/ first & having a solid grasp on Django models & query API. this is not exactly a fix for your question but more of a high-level suggestion after checking your codes and other related comments on the thread. These will help you develop GIS API more easily.