many-to-many in list display django

Question

class PurchaseOrder(models.Model):     product = models.ManyToManyField('Product')     vendor = models.ForeignKey('VendorProfile')     dollar_amount = models.FloatField(verbose_name='Price')   class Product(models.Model):    products = models.CharField(max_length=256)     def __unicode__(self):        return self.products 

I have that code. Unfortunately, the error comes in admin.py with the ManyToManyField

class PurchaseOrderAdmin(admin.ModelAdmin):     fields = ['product', 'dollar_amount']     list_display = ('product', 'vendor') 

The error says:

'PurchaseOrderAdmin.list_display[0]', 'product' is a ManyToManyField which is not supported.

However, it compiles when I take 'product' out of list_display. So how can I display 'product' in list_display without giving it errors?

edit: Maybe a better question would be how do you display a ManyToManyField in list_display?

Answer 1

You may not be able to do it directly. From the documentation of list_display

ManyToManyField fields aren’t supported, because that would entail executing a separate SQL statement for each row in the table. If you want to do this nonetheless, give your model a custom method, and add that method’s name to list_display. (See below for more on custom methods in list_display.)

You can do something like this:

class PurchaseOrderAdmin(admin.ModelAdmin):     fields = ['product', 'dollar_amount']     list_display = ('get_products', 'vendor')      def get_products(self, obj):         return "\n".join([p.products for p in obj.product.all()]) 

OR define a model method, and use that

class PurchaseOrder(models.Model):     product = models.ManyToManyField('Product')     vendor = models.ForeignKey('VendorProfile')     dollar_amount = models.FloatField(verbose_name='Price')      def get_products(self):         return "\n".join([p.products for p in self.product.all()]) 

and in the admin list_display

list_display = ('get_products', 'vendor')