flaf/drf-basic.md

## drf-basic.md

      
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              drf-basic.md
            
          
    Warning, I'm a Django beginner. I'm using Django 4.0.2 and DRF 3.13.1. My project (very basic) uses the default SQLite DB and I have 2 questions. Here is my code:
### My models.py ###

from django.db import models


class Template(models.Model):
    name = models.CharField(max_length=300, unique=True)
    root_partition = models.CharField(max_length=300)
    lvm = models.BooleanField()

    def __str__(self):
        return self.name


class VM(models.Model):
    fqdn = models.CharField(max_length=300, unique=True)
    created = models.DateTimeField(auto_now_add=True)
    from_template = models.ForeignKey(Template, on_delete=models.CASCADE)

    def __str__(self):
        return self.fqdn

    class Meta:
        ordering = ['fqdn']

#----------------------------------------------------------------

#### My serializers.py ###

from rest_framework import serializers
from .models import VM, Template

class TemplateSerializer(serializers.ModelSerializer):

    class Meta:
      model = Template
      fields = ['name', 'root_partition', 'lvm']


class VMSerializer(serializers.ModelSerializer):

    class Meta:
      model = VM
      fields = ['fqdn', 'created', 'from_template']

    from_template = serializers.StringRelatedField(many=False, read_only=False)
    #from_template = TemplateSerializer(many=False)

#----------------------------------------------------------------

#### My views.py ###

from django.shortcuts import render
from rest_framework import generics
from .models import VM, Template
from .serializers import VMSerializer, TemplateSerializer

class VMList(generics.ListCreateAPIView):
    queryset = VM.objects.all()
    serializer_class = VMSerializer

class TemplateList(generics.ListCreateAPIView):
    queryset = Template.objects.all()
    serializer_class = TemplateSerializer
GET requests are OK, as you can see:
$ curl -s http://127.0.0.1:8000/api/templates | jq
[
  {
    "name": "redhat-8-5",
    "root_partition": "/dev/root-part",
    "lvm": true
  },
  {
    "name": "ubuntu-20-04",
    "root_partition": "/dev/root-part",
    "lvm": false
  },
  {
    "name": "ubuntu-20-04-lvm",
    "root_partition": "/dev/root/part1",
    "lvm": true
  },
  {
    "name": "redhat-8-3",
    "root_partition": "/dev/root/partx",
    "lvm": true
  }
]

$ curl -s http://127.0.0.1:8000/api/vms | jq
[
  {
    "fqdn": "mariadb.in.ac-versailles.fr",
    "created": "2022-02-11T00:42:33.473687Z",
    "from_template": "ubuntu-20-04-lvm"
  },
  {
    "fqdn": "srv-1.flaf.fr",
    "created": "2022-02-11T00:41:14.897579Z",
    "from_template": "redhat-8-5"
  },
  {
    "fqdn": "toto.domain.tld",
    "created": "2022-02-11T00:41:00.931524Z",
    "from_template": "redhat-8-5"
  },
  {
    "fqdn": "www.google.com",
    "created": "2022-02-12T16:16:24.522782Z",
    "from_template": "redhat-8-3"
  },
  {
    "fqdn": "x.toto.fr",
    "created": "2022-02-12T16:14:51.645851Z",
    "from_template": "redhat-8-3"
  }
]
Question 1: During the second curl above, I have these SQL requests:
(0.000) SELECT "vbot_template"."id", "vbot_template"."name", "vbot_template"."root_partition", "vbot_template"."lvm" FROM "vbot_template" WHERE "vbot_template"."id" = 3 LIMIT 21; args=(3,); alias=default
(0.000) SELECT "vbot_template"."id", "vbot_template"."name", "vbot_template"."root_partition", "vbot_template"."lvm" FROM "vbot_template" WHERE "vbot_template"."id" = 1 LIMIT 21; args=(1,); alias=default
(0.000) SELECT "vbot_template"."id", "vbot_template"."name", "vbot_template"."root_partition", "vbot_template"."lvm" FROM "vbot_template" WHERE "vbot_template"."id" = 1 LIMIT 21; args=(1,); alias=default
(0.000) SELECT "vbot_template"."id", "vbot_template"."name", "vbot_template"."root_partition", "vbot_template"."lvm" FROM "vbot_template" WHERE "vbot_template"."id" = 4 LIMIT 21; args=(4,); alias=default
(0.000) SELECT "vbot_template"."id", "vbot_template"."name", "vbot_template"."root_partition", "vbot_template"."lvm" FROM "vbot_template" WHERE "vbot_template"."id" = 4 LIMIT 21; args=(4,); alias=default

Two identical requests are repeated twice. Why? Why doesn't Django keep a first request in memory to avoid repetition?
Question 2: If I want to POST de VM via the HTML form of the API, only the fqdn is settable and the from_template field is absent. So it's impossible to make a POST. I have an exception because the field from_template is not set:
NOT NULL constraint failed: vbot_vm.from_template_id

Why? How to fix it to allow a POST directly via the HTML form?
Thanks for your help.