Django admin: handling relations with large tables

One of the reasons, that Django became so popular, is that it provides a set of flexible administrative tools. You may setup your data management dashboard in relatively short time using some predefined classess.

A typical object admin view consists of a ModelForm of an appropriate model, and some basic actions (save, add, delete).  As you probably know, foreign keys are often represented as HTML select inputs. This works cool, when the related table is not vertically long, for example: electronic equipment brands. In such cases the combobox works well.

Imagine a situation when, the foreign key points to a user record,  a purchase order, or any other relation that does not have a limited number of rows. According to the previous example, the combo box should have thousands of options. This is a real performance killer, the ORM has to fetch the whole user/purchase order table in order to display a single object in an editable admin view. Don't be surprised if your query gets killed with the "2006 - MySQL server has gone away" status.

There is a simple way to solve this: instead of selecting the whole table for presenting available options, we may present only the currently related object (its primary key). To achieve this, we must mark the foreign keys as raw_id_fields. Below sample usage:

 

class PurchaseReportAdmin(admin.ModelAdmin):                                                                   
    #(...) other fields                                                                                 
    raw_id_fields = ['purchase_order']
admin.site.register(PurchaseReport, PurchaseReportAdmin )

Yes, it's as simple as that. Keep in mind, that in many cases using raw id fields won't be necessary, but when it come to vertically huge tables - it's a good time/performance saving solution.

Cheers!
KR