“ ForeignKey”对象没有属性

Question

When I try to make migrations for the following models:

class Location(models.Model):
    name = models.CharField(max_length=200)
    latitude = models.FloatField
    longitude = models.FloatField
    altitude = models.IntegerField

    def _str_(self):
        return self.name

    def getLatitude(self):
        return self.latitude

    def getLongitude(self):
        return self.longitude

class Distance(models.Model):
    placeA = models.ForeignKey(Location, on_delete=models.CASCADE)
    placeB = models.ForeignKey(Location, on_delete=models.CASCADE)
    placeAlatitude = placeA.getLatitude()
    placeBlatitude = placeB.getLatitude()
    placeAlongitude = Location.objects.select_related().get(placeA.longitude)
    placeBlongitude = Location.objects.select_related().get(placeB.longitude)
    distance = models.FloatField(default = 0.0)

I am getting the error:

'ForeignKey' object has no attribute 'getLatitude'

I get a similar error if I try to directly access the latitude directly ( placeA.latitude )

What am I doing wrong? I am new to using the Django framework.

Answer 1

In your model, you are defining the structure. You can't use

placeAlatitude = placeA.getLatitude()
placeBlatitude = placeB.getLatitude() 

placeAlatitude and placeBlatitude must be define the type of model. You can't simply return value.

From analyzing your model these two fields are not necessary it is redundant values(same case for placeAlongitude and placeBlongitude). You defined a foreign key relation to location. So you can access longitude and latitude by using that relation.

Answer 2

First of all there is likely an error in your Location model: you here do not construct the FloatField s and IntegerField : you only pass a reference to the class, you do not "call" it. So in order to define these columns, you should add parenthesis:

class Location(models.Model):
    name = models.CharField(max_length=200)
    latitude = models.FloatField
    longitude = models.FloatField
    altitude = models.IntegerField

    # ...

Next you can not define placeAlatitude , etc. with placeA.GetLatitude() , at class level placeA is a ForeignKey object, not a Location , object, you can however define a @property here that will, for a Distance object, fetch the correct attribute of the related objects:

class Distance(models.Model):
    placeA = models.ForeignKey(Location, on_delete=models.CASCADE)
    placeB = models.ForeignKey(Location, on_delete=models.CASCADE)
    distance = models.FloatField(default = 0.0)

    @property
    def (self):
        return self.placeA.latitude

    @property
    def (self):
        return self.placeB.latitude

    @property
    def (self):
        return self.placeA.longitude

    @property
    def (self):
        return self.placeB.longitude