CODEWITHSUNDEEP
djangodjango-models
Coderji
Coderji

Reputation: 7745

Django - Modify field value after every query

I am fairly new to Django coming from Laravel background. I would like to modify a field value everytime I query it. For example, every time you query firstname@User you return the Capitalized firstname. In Laravel this is known as Accessors but apparantely Accessors have different meaning in Django. For my case, I have a key-value table called Meta where the value field can be of any type:

class Meta(models.Model):
    key = models.CharField(max_length=30)
    value = models.TextField()
    model = models.ForeignKey('Model', on_delete=models.CASCADE)

and upon getting the value Meta.objects.get(key='foo'), I would like to return ast.literal_eval(value) to convert the string expression to the correct respective type. I did some research and only found the following:

What is the best choice to apply this function for everytime I query value filtering by the key

Upvotes: 0

Views: 338

Answers (2)

MaximeK
MaximeK

Reputation: 2061

a @property is a good approach, but if you will access a lot of time ast.literal_eval and the processing is costly, you can overrride the save method:

def __init__(self, *args, **kwargs):                                         
    super(Meta, self).__init__(*args, **kwargs)                         
    self.__original_value = self.value

def save(self, **kwargs):
    if self.__original_value != self.value:
        self.value = ast.literal_eval(self.value)
    super(Meta, self).save()

The init will pick the value before the update

Upvotes: 1

Daniel Roseman
Daniel Roseman

Reputation: 599630

You could use a custom field, but the easiest thing here is to use a property.

class Meta(models.Model):
    value = models.TextField()

    @property
    def converted_value(self):
        return ast.literal_eval(self.value)

Now you can access my_meta.converted_value whenever you need that converted value.

Upvotes: 2

Related Questions