Correct way to use get_or_create?
Question:
I’m trying to use get_or_create for some fields in my forms, but I’m getting a 500 error when I try to do so.
One of the lines looks like this:
customer.source = Source.objects.get_or_create(name="Website")
The error I get for the above code is:
Cannot assign "(<Source: Website>, False)": "Customer.source"
must be a "Source" instance.
Answers:
get_or_create returns a tuple.
customer.source, created = Source.objects.get_or_create(name="Website")
From the documentation get_or_create:
# get_or_create() a person with similar first names.
p, created = Person.objects.get_or_create(
first_name='John',
last_name='Lennon',
defaults={'birthday': date(1940, 10, 9)},
)
# get_or_create() didn't have to create an object.
>>> created
False
Explanation:
Fields to be evaluated for similarity, have to be mentioned outside defaults. Rest of the fields have to be included in defaults. In case CREATE event occurs, all the fields are taken into consideration.
It looks like you need to be returning into a tuple, instead of a single variable, do like this:
customer.source,created = Source.objects.get_or_create(name="Website")
The issue you are encountering is a documented feature of get_or_create.
When using keyword arguments other than “defaults” the return value of get_or_create is an instance. That’s why it is showing you the parens in the return value.
you could use customer.source = Source.objects.get_or_create(name="Website")[0] to get the correct value.
Here is a link for the documentation:
http://docs.djangoproject.com/en/dev/ref/models/querysets/#get-or-create-kwargs
get_or_create() returns a tuple:
customer.source, created = Source.objects.get_or_create(name="Website")
-
created → has a boolean value, is created or not.
-
customer.source → has an object of get_or_create() method.
Following @Tobu answer and @mipadi comment, in a more pythonic way, if not interested in the created flag, I would use:
customer.source, _ = Source.objects.get_or_create(name="Website")
get_or_create method would actually return a tuple.
The trick with the get_or_create method is that it actually returns a tuple of (object, created). The first element is an instance of the model you are trying to retrieve and the second is a boolean flag to tell if the instance was created or not. True means the instance was created by the get_or_create method and False means it was retrieved from the database
So you can do something like to get the source instance
``` customer.source = Source.objects.get_or_create(name="Website")[0]
```
Important warning.
you should take care of the following before using the get_or_create , https://docs.djangoproject.com/en/4.0/ref/models/querysets/.
….
Warning
This method is atomic assuming that the database enforces uniqueness of the keyword arguments (see unique or unique_together). If the fields used in the keyword arguments do not have a uniqueness constraint, concurrent calls to this method may result in multiple rows with the same parameters being inserted.
I’m trying to use get_or_create for some fields in my forms, but I’m getting a 500 error when I try to do so.
One of the lines looks like this:
customer.source = Source.objects.get_or_create(name="Website")
The error I get for the above code is:
Cannot assign "(<Source: Website>, False)": "Customer.source"
must be a "Source" instance.
get_or_create returns a tuple.
customer.source, created = Source.objects.get_or_create(name="Website")
From the documentation get_or_create:
# get_or_create() a person with similar first names.
p, created = Person.objects.get_or_create(
first_name='John',
last_name='Lennon',
defaults={'birthday': date(1940, 10, 9)},
)
# get_or_create() didn't have to create an object.
>>> created
False
Explanation:
Fields to be evaluated for similarity, have to be mentioned outside defaults. Rest of the fields have to be included in defaults. In case CREATE event occurs, all the fields are taken into consideration.
It looks like you need to be returning into a tuple, instead of a single variable, do like this:
customer.source,created = Source.objects.get_or_create(name="Website")
The issue you are encountering is a documented feature of get_or_create.
When using keyword arguments other than “defaults” the return value of get_or_create is an instance. That’s why it is showing you the parens in the return value.
you could use customer.source = Source.objects.get_or_create(name="Website")[0] to get the correct value.
Here is a link for the documentation:
http://docs.djangoproject.com/en/dev/ref/models/querysets/#get-or-create-kwargs
get_or_create() returns a tuple:
customer.source, created = Source.objects.get_or_create(name="Website")
-
created→ has a boolean value, is created or not. -
customer.source→ has an object ofget_or_create()method.
Following @Tobu answer and @mipadi comment, in a more pythonic way, if not interested in the created flag, I would use:
customer.source, _ = Source.objects.get_or_create(name="Website")
get_or_create method would actually return a tuple.
The trick with the get_or_create method is that it actually returns a tuple of (object, created). The first element is an instance of the model you are trying to retrieve and the second is a boolean flag to tell if the instance was created or not. True means the instance was created by the get_or_create method and False means it was retrieved from the database
So you can do something like to get the source instance
``` customer.source = Source.objects.get_or_create(name="Website")[0]
```
Important warning.
you should take care of the following before using the get_or_create , https://docs.djangoproject.com/en/4.0/ref/models/querysets/.
….
Warning
This method is atomic assuming that the database enforces uniqueness of the keyword arguments (see unique or unique_together). If the fields used in the keyword arguments do not have a uniqueness constraint, concurrent calls to this method may result in multiple rows with the same parameters being inserted.