Can't save new objects in Django full-text search with PostgreSQL - django

Question

I'm following this post on how to add full-text functionality to my Django app. I have the following model:
class CustomUser(AbstractUser):
email = models.EmailField(_('email address'), unique=True)
class Author(models.Model):
user = models.OneToOneField(settings.AUTH_USER_MODEL,on_delete = models.CASCADE)
name = models.CharField(max_length = 250)
alternative_names = ArrayField(models.CharField(max_length = 250),blank=True,null=True)
name_norm = models.CharField(max_length = 250,blank=True,null = True)
slug = models.CharField(max_length = 250,unique = True)
photo = models.ImageField(upload_to = 'imgs/users/%Y/%m/%d',blank = True)
search_vector = SearchVectorField(null=True)
def save(self, *args, **kwargs):
self.search_vector = (SearchVector('name', weight='A') )
super().save(*args, **kwargs)`enter code here`
And when I try to save a new author with save:
autor = Author(user = utilizador,name = author_name,alternative_names = alternative_names,name_norm = name_norm,slug = slug)
autor.save()
I get the error:
Traceback (most recent call last):
File "populate_v2.py", line 140, in <module>
autor.save()
File "/home/mwon/NewArquivoOpiniao/webapp/colunadeopiniao/accounts/models.py", line 57, in save
super().save(*args, **kwargs)
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/base.py", line 748, in save
self.save_base(using=using, force_insert=force_insert,
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/base.py", line 785, in save_base
updated = self._save_table(
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/base.py", line 890, in _save_table
results = self._do_insert(cls._base_manager, using, fields, returning_fields, raw)
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/base.py", line 927, in _do_insert
return manager._insert(
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/manager.py", line 82, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/query.py", line 1204, in _insert
return query.get_compiler(using=using).execute_sql(returning_fields)
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1393, in execute_sql
for sql, params in self.as_sql():
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1336, in as_sql
value_rows = [
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1337, in <listcomp>
[self.prepare_value(field, self.pre_save_val(field, obj)) for field in fields]
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1337, in <listcomp>
[self.prepare_value(field, self.pre_save_val(field, obj)) for field in fields]
File "/home/mwon/NewArquivoOpiniao/env3.8/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1263, in prepare_value
raise ValueError(
ValueError: Failed to insert expression "SearchVector(Col(accounts_author, accounts.Author.name), weight=A)" on accounts.Author.search_vector. F() expressions can only be used to update, not to insert.
Django version: 3.0.11

Answer 1

F() expressions can only be used to update, not to insert.
I'm no expert on VectorField, but maybe the weight='A' is causing the F() expression. Does it work without weight, as shown in the tutorial you refer to?
Otherwise, try an update:
Author.objects.all().update(search_vector=SearchVector('name', weight='A'))

Answer 2

The error message is saying that you are trying to insert a value into the search_vector field when creating a new object of Author, but the SearchVector class only supports updating existing objects, not creating new ones. To solve this, you can change the implementation of the save method to update the search_vector field after the object has been created:
def save(self, *args, **kwargs):
super().save(*args, **kwargs)
Author.objects.filter(pk=self.pk).update(search_vector=SearchVector('name', weight='A'))
This way, you can create the object first, and then update the vector.