How to add a calculated field to a Django model

Question

I have a simple Employee model that includes firstname, lastname and middlename fields.

On the admin side and likely elsewhere, I would like to display that as:

lastname, firstname middlename 

To me the logical place to do this is in the model by creating a calculated field as such:

from django.db import models from django.contrib import admin  class Employee(models.Model):     lastname = models.CharField("Last", max_length=64)     firstname = models.CharField("First", max_length=64)     middlename = models.CharField("Middle", max_length=64)     clocknumber = models.CharField(max_length=16)     name = ''.join(         [lastname.value_to_string(),         ',',          firstname.value_to_string(),         ' ',          middlename.value_to_string()])      class Meta:         ordering = ['lastname','firstname', 'middlename']  class EmployeeAdmin(admin.ModelAdmin):     list_display = ('clocknumber','name')     fieldsets = [("Name", {"fields":(("lastname", "firstname", "middlename"), "clocknumber")}),         ]  admin.site.register(Employee, EmployeeAdmin) 

Ultimately what I think I need is to get the value of the name fields as strings. The error I am getting is value_to_string() takes exactly 2 arguments (1 given). Value to string wants self, obj. I am not sure what obj means.

There must be an easy way to do this, I am sure I am not the first to want to do this.

Edit: Below is my code modified to Daniel's answer. The error I get is:

django.core.exceptions.ImproperlyConfigured:      EmployeeAdmin.list_display[1], 'name' is not a callable or an      attribute of 'EmployeeAdmin' of found in the model 'Employee'. 

from django.db import models from django.contrib import admin  class Employee(models.Model):     lastname = models.CharField("Last", max_length=64)     firstname = models.CharField("First", max_length=64)     middlename = models.CharField("Middle", max_length=64)     clocknumber = models.CharField(max_length=16)      @property     def name(self):         return ''.join(             [self.lastname,' ,', self.firstname, ' ', self.middlename])      class Meta:         ordering = ['lastname','firstname', 'middlename']  class EmployeeAdmin(admin.ModelAdmin):     list_display = ('clocknumber','name')     fieldsets = [("Name", {"fields":(("lastname", "firstname", "middlename"), "clocknumber")}), ]  admin.site.register(Employee, EmployeeAdmin) 

Answer 1

That's not something you do as a field. Even if that syntax worked, it would only give the value when the class was defined, not at the time you access it. You should do this as a method, and you can use the @property decorator to make it look like a normal attribute.

@property def name(self):     return ''.join(         [self.lastname,' ,', self.firstname, ' ', self.middlename]) 

self.lastname etc appear as just their values, so no need to call any other method to convert them.