How to calculate total for all model objects that have another common value

Question

Trying to create a calculation column in a table where it returns the sum of all allocated_hours for any db row that has a matching user_id. Currently I am getting "0" in the column for each item. What am I missing here? Thanks for the help.

Note that I am using django tables2.

#model.py
class Allocation(models.Model):
    user_id = models.ForeignKey(Resource)
    project_id = models.ForeignKey(Project)
    week = models.DateField(default=timezone.now)
    allocated_hours = models.IntegerField(default=0)
    actual_hours = models.IntegerField(default=0)



    def __str__(self):
        return '%s - %s' % (self.user_id, self.project_id)

    def allocation_total(self):
        alltotal = 0
        for i in Allocation.objects.values_list('user_id'):
            if i == Allocation.user_id:
                alltotal += Allocation.allocated_hours
        return alltotal

-

#tables.py
class Project_Resource_table(tables.Table):
    role = tables.Column(accessor='user_id.resource_type')
    name = tables.Column(accessor='user_id.resource_name')
    allocation = tables.Column(accessor='allocation_total')

class Meta:
    model = Allocation
    exclude = ('id', 'user_id', 'project_id', 'week', 'allocated_hours', 'actual_hours')
    sequence = ('role', 'name', 'allocation')

Answer 1

I was able to work around the issue with a new function.

    def total_allocation(self):
        a = Allocation.objects.filter(project_id=self.project_id)
        total = 0
        for i in a:
            if i.user_id == self.user_id:
                total += i.allocated_hours
        return total

Thanks for the suggestions. Still curious if there is a way for me to do this in tables.py rather than adding it to my models.py. I was unable to get that to work.