CODEWITHSUNDEEP
pythondjangofunctionobjectdjango-models
Stephen
Stephen

Reputation: 6319

How to use "get_or_create()" in Django?

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.

Upvotes: 327

Views: 377829

Answers (8)

Super Kai - Kazuya Ito
Super Kai - Kazuya Ito

Reputation: 1

get_or_create() returns the tuple which contains 2 values and the 1st value is an object and the 2nd value is the boolean value which indicates that a new object is created or not as shown below:

 # 1st   # 2nd
(object, boolean)

So, if you want both an object and a boolean value, put one more variable created after customer.source as shown below:

                 # Here
customer.source, created = Source.objects.get_or_create(name="Website")
# object         # boolean

And, if you want only an object without a boolean value, put [0] just after get_or_create() as shown below:

                                                       # Here ↓↓↓
customer.source = Source.objects.get_or_create(name="Website")[0]
# object

And, if you want only a boolean value without an object put [1] just after get_or_create() as shown below:

                                               # Here ↓↓↓
created = Source.objects.get_or_create(name="Website")[1]
# boolean

Upvotes: 4

alfonsoolavarria
alfonsoolavarria

Reputation: 1225

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.

Upvotes: 1

SHUBHAM JHA
SHUBHAM JHA

Reputation: 11

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]
 ```

Upvotes: 1

Tushar Patil
Tushar Patil

Reputation: 1479

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.

Upvotes: 35

Astra
Astra

Reputation: 11211

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")

Upvotes: 532

jbondia
jbondia

Reputation: 273

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")

Upvotes: 24

wlashell
wlashell

Reputation: 898

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

Upvotes: 7

Tobu
Tobu

Reputation: 25426

get_or_create returns a tuple.

customer.source, created = Source.objects.get_or_create(name="Website")

Upvotes: 46

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