Non-relational field given in select_related: ' '. Choices are: (none)

Question

I have two models from different apps:

class Measure(models.Model):
    date = models.DateTimeField(default="2018-01-23 15:55")
    average = models.FloatField(default=0)

class Sensor(models.Model):
    measure=models.ForeignKey(Measure, on_delete=models.CASCADE)
    value= models.FloatField(default=0)

I'm calling all data coming from sensors as follow:

new_context = Sensor.objects.select_related('measure__date')

However, I receive this error:

django.core.exceptions.FieldError: Non-relational field given in select_related: 'date'. Choices are: (none)

from documentation, I should be using select_related instead of prefetch_related, and the call seems to be coherent.

Am I missing something?

Graffito

Just do Sensor.objects.select_related('measure'). After that you may get the attributes from the queryset. – Seduction

Similar issues can arise when upgrading old Django code. This type of error would silently fail before Django 1.10 (or 1.8 for non-nested). See release notes for 1.10 and 1.8. – Structure

Answer 1

In select_related only fields that are ForeignKey should be set. In your case the issue it that date field is a DateTimeField and not ForeignKey.

So in order to solve it just do it:

new_context = Sensor.objects.select_related('measure')

You can see examples of using syntax in docs.

Sarmentum

thanks! By doing this if I call print (new_context[0]) i get Sensor object (688). However, if I do print (new_context[0].date) then I get the error AttributeError: 'Sensor' object has no attribute 'date'. How is that possible? – Graffito

@Graffito ].measure.date – Unalloyed