Django rest framework Serializer Save() problem - django

Question

Hi there i am new ot django and django rest framework and i am having torouble when using serializers with PrimarayKeyTelatedFields() the code below is my code for my models.py
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=50)
age = models.IntegerField(default=0)
class Book(models.Model):
name = models.CharField(max_length=40)
author = models.ForeignKey(to=Author, on_delete=models.CASCADE)
below is my serializer code
from rest_framework import serializers
from books.models import Book, Author
class BookSerializer(serializers.ModelSerializer):
author_id = serializers.PrimaryKeyRelatedField(many=False,
queryset=Author.objects.all())
class Meta:
model = Book
fields = ['id', 'name', 'author_id']
class AuthorSerializer(serializers.ModelSerializer):
class Meta:
model = Author
fields = ['id', 'name', 'age']
and when i try to execute following commands in shell
>>from books.api.serializers import BookSerializer, AuthorSerializer
>> play1 = BookSerializer(data = { 'author_id':1 ,'name':'book1' })
>>play1.is_valid()
True
>>play1.save()
After executing above i got the huge error as i pasted below
Traceback (most recent call last):
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 1988, in get_prep_value
return int(value)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'Author'
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\rest_framework\serializers.py", line 962, in create
instance = ModelClass._default_manager.create(**validated_data)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\query.py", line 514, in create
obj.save(force_insert=True, using=self.db)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 806, in save
self.save_base(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 857, in save_base
updated = self._save_table(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 1000, in _save_table
results = self._do_insert(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 1041, in _do_insert
return manager._insert(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\query.py", line 1434, in _insert
return query.get_compiler(using=using).execute_sql(returning_fields)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1620, in execute_sql
for sql, params in self.as_sql():
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1547, in as_sql
value_rows = [
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1548, in <listcomp>
[
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1549, in <listcomp>
self.prepare_value(field, self.pre_save_val(field, obj))
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1487, in prepare_value
value = field.get_db_prep_save(value, connection=self.connection)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\related.py", line 1126, in get_db_prep_save
return self.target_field.get_db_prep_save(value, connection=connection)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 910, in get_db_prep_save
return self.get_db_prep_value(value, connection=connection, prepared=False)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 2668, in get_db_prep_value
value = self.get_prep_value(value)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 1990, in get_prep_value
raise e.__class__(
TypeError: Field 'id' expected a number but got <Author: Author object (1)>.
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\rest_framework\serializers.py", line 212, in save
self.instance = self.create(validated_data)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\rest_framework\serializers.py", line 981, in create
raise TypeError(msg)
TypeError: Got a `TypeError` when calling `Book.objects.create()`. This may be because you have a writable field on the serializer class that is not a valid argument to `Book.objects.create()`. You may need to make the field read-only, or override the BookSerializer.create() method to handle this correctly.
Original exception was:
Traceback (most recent call last):
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 1988, in get_prep_value
return int(value)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'Author'
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\rest_framework\serializers.py", line 962, in create
instance = ModelClass._default_manager.create(**validated_data)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\query.py", line 514, in create
obj.save(force_insert=True, using=self.db)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 806, in save
self.save_base(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 857, in save_base
updated = self._save_table(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 1000, in _save_table
results = self._do_insert(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\base.py", line 1041, in _do_insert
return manager._insert(
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\query.py", line 1434, in _insert
return query.get_compiler(using=using).execute_sql(returning_fields)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1620, in execute_sql
for sql, params in self.as_sql():
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1547, in as_sql
value_rows = [
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1548, in <listcomp>
[
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1549, in <listcomp>
self.prepare_value(field, self.pre_save_val(field, obj))
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\sql\compiler.py", line 1487, in prepare_value
value = field.get_db_prep_save(value, connection=self.connection)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\related.py", line 1126, in get_db_prep_save
return self.target_field.get_db_prep_save(value, connection=connection)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 910, in get_db_prep_save
return self.get_db_prep_value(value, connection=connection, prepared=False)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 2668, in get_db_prep_value
value = self.get_prep_value(value)
File "C:\Users\Admin\AppData\Local\Programs\Python\Python38\lib\site-packages\django\db\models\fields\__init__.py", line 1990, in get_prep_value
raise e.__class__(
TypeError: Field 'id' expected a number but got <Author: Author object (1)>.

Answer 1

you passed here an object instead of id..
author_id = serializers.PrimaryKeyRelatedField(many=False,
queryset=Author.objects.all())
you should pass an id like this
author_id = serializers.PrimaryKeyRelatedField(many=False,
queryset=Author.objects.get(id=request.user.id))
Remember whatever you queried it should be an int value not str or object

Answer 2

Cause
The problem is caused by setting author_id with serializer.PrimaryKeyRelatedField
Explanation
Django will internally auto-create an attribute for related fields (ForeignKey, OneToOneField, ...) with the suffix _id appending to the declared field name. The data type of this field is a number. In this case, the author field in Book will have an attribute called author_id. The problem comes from serializer.PrimaryKeyRelatedField returning a model instance in the serializer's validated data, causing field author_id to be set with Author instance. Resulting in an error.
Solution
Rename author_id attribute to author.
class BookSerializer(serializers.ModelSerializer):
author = serializers.PrimaryKeyRelatedField(queryset=Author.objects.all())
class Meta:
model = Book
fields = ['id', 'name', 'author']