Django Admin App

These days Admin sites are an integral part of any website. Administrators, author and staff members use admin site to manage the content of the main site. Django provides an admin site right out of the box for managing content, so that you can just focus on building features that you need instead of creating old boring admin sites. However, it doesn’t mean that you can’t roll out your own admin site. If Django admin site doesn’t meet your requirements you can create your own admin site from scratch. In this series, however, we will not be doing that. If you are interested in building your own admin site, you have two options. The first is to wait for this series to finish, by then you will have enough knowledge to create your own admin site. The other option is to checkout my [Django 1.10](https://overiq.com/django/1.10/intro-to-django/) series in which I have created an admin site from scratch). With further ado. Let’s get started with Django admin app.

Creating a superuser

To use admin site we first have to create a superuser. In the terminal enter the following command.

First, you will be prompted to enter a username.

Next, enter an email address. This is optional.

Finally, enter a password and confirm it by retyping.

Now you can login into the Django admin site.

Django Admin Site – The First Look

Start the development server if not already running and point your browser to
http://localhost:8000/admin. You will see a login page like this:

Enter username and password and hit enter. On success, you will be redirected to the index page of Django admin site.

The index page shows a list of models available in your project. Currently, it is showing only Group and User models from the django.contrib.auth app (the second app in the INSTALLED_APPS setting). To display models from our djangobin app, we have to do a little configuration, which is the topic of the next section.

The Group model is used to organize permissions and the User model represents a site user. Managing permissions is out of scope for this series. As a result, our discussion will be limited only to the User model.

Click the “Users” links and you will be taken to the User list page, which looks like this:

The list page shows a list of objects from a particular model. The User list page shows a list of User objects in the database. As you can see in the above figure, currently, there is only one User object in the database which we have created in the previous section.

In addition to displaying User objects, the User list page allows us to do the following tasks:

  • Add new user.
  • Modify existing user.
  • Search and filter users.
  • Sort the user data by clicking on the column header.
  • Delete user.

The Django admin site is quite self-explanatory. Any non-technical user should be able to use it without any problem. Try navigating the site on your own. Add some new users and modify existing one, this will give you a better idea of how Django admin site works. In the next section, we will add models from the djangobin app to the Django admin site.

Adding models to Django admin

By default, Django admin site doesn’t load any model from the apps we create. To add a model to the Django admin you have to modify admin.py file available inside every app directory. Open admin.py inside the djangobin app i.e djangobin/django_project/djangobin. At this point, admin.py should look like this:

djangobin/django_project/djangobin/admin.py

Modify the file as follows:

djangobin/django_project/djangobin/admin.py

In line 2, we are importing models from the djangobin app. To add a model to the Django admin site, pass the name of the model to the admin.site.register() method.

Open your browser and visit http://localhost:8000/admin/. You should see models from the djangobin app as follows:

Important features of Django admin

In this section, we will discuss some important aspects of Django admin site. Our discussion will be restricted to the following points:

  1. __str__() method.
  2. Model Relationships.
  3. Data validation.
  4. Django tracking system.
  5. Widgets.

__str__() method

Navigate to the Snippet list page ( i.e http://localhost:8000/admin/djangobin/snippet/) by clicking “Snippets” link in the Django admin home page. You will be displayed a page like this:

So what makes Django admin to show Snippet objects in this form?

By default, Django admin displays the value returned by the __str__() method defined in the model class. For Snippet models, the __str__() method is defined as follows:

djangobin/django_project/djangobin/models.py

Modify the __str__() method of the Snippet model as follows:

Refresh the Snippet list page (http://localhost:8000/admin/djangobin/snippet/) and it should now look like this:

As you can see Django admin site has picked-up our changes in the __str__() method and started displaying language of the snippet. We don’t want these changed to be permanent because in next section will display Snippet’s Language in the separate column. So lets revert back to our original __str__() definition.

Refresh the Snippet list page again, and it should be back to the way it was.

Model Relationships in Django admin site

This is one of the most important things that deserves some explanation. Recall that our
Snippet model has following relationships:

  1. A one-to-many relationship with Author model.
  2. A one-to-many relationship with Language model.
  3. A many-to-many relationship with Tag model.

For reference, this is how the Snippet model is defined.

djangobin/django_project/djangobin/models.py

We can see how Django admin site manages model relationships by adding a new snippet or editing an existing snippet.

Let’s add a new snippet by clicking “ADD SNIPPET +” button at the top right corner of the snippet list page.

Django uses a single-selection <select> box to represent one-to-many relationships. We have two one-to-many relationships. The first is between Snippet and Language and the second is between Snippet and Author. The language and author field of the Snippet model is represented using a single-selection <select> element as follows:

You can also add a new language/author by clicking + link beside the <select> tag. Clicking the + icon opens a pop-up window which allows you to add a new object to the database.

Once a language or author is selected, you can also edit them by clicking yellow pencil icon beside the drop-down.

Similarly, Django uses a multiple-selection <select> box to represent a many-to-many relationship. As a snippet can have one or more than two tags, the multiple selection <select> box allows you to select more than one tag by holding Ctrl key while selecting.

You can also add a new tag by clicking the + link.

The language and the author field of the Snippet model is defined with on_delete parameter set to models.CASCADE. As a result, deleting an author or language will also delete its associated snippets.

Django admin Site Handles Validation

Django admin site automatically provides input validation. Try saving a blank snippet or enter some invalid characters in the Slug field. You will see errors as follows:

In Add snippet (and Change snippet) form, all the fields are required except the title (we are not taking account of created_on field which has auto_now_add parameter set True). The title field is optional because we have set blank=True while defining it in the Snippet model.

Also, note that the Django admin site shows required fields in bold.

Django tracking system.

Django keeps track of the changes you have made to the object. To view the change log click on the “History” link in the object editing page.

If you haven’t made any changes to the object then you will get the following message.

Widgets

The widgets refer to the way a Model field is displayed in the form. Django provides widgets on the basis of field types defined in the model. For example, a
CharField is displayed as an <input> element, ForeignKey as a select-box,
BooleanField as a checkbox and so on. We will learn more about widgets and how to override them in Django Form Basics chapter.

Customizing the List page

Open your browser and visit Language list page (http://localhost:8000/admin/djangobin/language/) by clicking “Languages” link on the index page of Django admin site.

This page is similar to User list page (http://localhost:8000/admin/auth/user/) but there are subtle differences.

  1. Unlike User list page there is no search bar.
  2. No filters on the right-hand side.
  3. The Language model consists of 7 fields (name, lang_code, slug, mime, file_extension, created_on and updated_on) but only name is visible.
  4. We can’t sort by clicking on the column header.

To customize the appearance of models on the list page, we use ModelAdmin class. The ModelAdmin class provides several attributes which allow us to change how a model is displayed in the list page. All these attributes are defined on the subclass of ModelAdmin in the admin.py file of the app. The following is a list of some common attributes of ModelAdmin.

* list_display – It controls which model fields to display on the list page. It accepts a list or tuple of field names. In addition to displaying fields, it also makes them sortable. For example,

This will display data from name, email and created_on fields from the model class and also makes them sortable.

* search_fields – This attribute enables the search function on the list page. It accepts a list or tuple of field names where you want to search. It performs a case-insensitive search. For example:

* ordering – It specifies how the list of objects should be ordered in the list page. It takes a list or tuple of field names. For example:

This will display a list of objects in descending order by name. Note that this option will override the ordering attribute of the inner Meta class.

* list_filter – This attribute activates the filtering bar on the right side of the list page. It accepts a list or tuple of field names. Django automatically provides different shortcuts to filter the objects based on the type of the field. For example, if the field is of type DateField then Django provides Today, Past 7 days, This month and This year shortcuts. Similarly, if the field is of type BooleanField then Django provides All, Yes and No shortcuts.

* date_hierarchy – This attribute is specially designed to provide an intelligent date based drill-down navigation just above Action select box. It takes a string, not a list or tuple. As date_hierarchy creates date based filter, you are only allowed to specify a field of type DateField or DateTimeField only. Here is how this attribute looks like on the list page.

Let’s put some of the attributes to test. Open admin.py inside the djangobin app and create a class named LanguageAdmin which inherits from admin.ModelAdmin class as follows:

djangobin/django_project/djangobin/admin.py

To register the changes outlined by the LanguageAdmin class we pass its name as a second argument to the register() method which registers its corresponding model.

Refresh the Language list page and it will look like this:

Before we move ahead, let’s add some more classes in admin.py file to customize the appearance of Snippet and Tag models.

djangobin/django_project/djangobin/admin.py

Customizing Forms

To customize forms, the admin.ModelAdmin class provides following attributes.

1. fields – By default, the order of appearance of fields in the forms is same as that of fields in the model class. To change the order, list the fields in the order you want as a list or tuple. For example,

This will display the "title" field followed by the "created_on" field and then the "author" field at last.

In addition to ordering the field, you can also use this attribute to remove one or more fields from being edited/added entirely.

2. filter_horizontal – This attribute can only be used with ManyToManyField. By default, ManyToManyField field is displayed using a multiple selection <select> box. Selecting records from a small list is easy but what if there are hundreds or thousands of records? To make the selection easier Django provides filter_horizontal attribute. It accepts list or tuple of the field names of type ManyToManyField. It then creates a nice interface which allows searching through the records as well as view available records and chosen records.

Let’s use this attribute to change the way tags field of the Snippet model is rendered. Open admin.py and add filter_horizontal attribute towards the end of SnippetAdmin class as follows:

djangobin/django_project/djangobin/admin.py

Visit Add snippet or Change Snippet page. You will see a widget like this:

3. raw_id_fields – There is no doubt that filter_horizontal makes record selection easier. But if you have hundreds or thousands of records, loading all these at once could take a while. The solution is to use raw_id_fields instead of filter_horizontal.

It accepts list or tuple of the field names of type ManyToManyField or ForeignKey and creates an input box ( <input type="text" ... /> ) where you can enter primary key of the record.

Open admin.py file and comment out the filter_horizontal attribute we have added to SnippetAdmin class in the previous step. And then add raw_id_fields attribute just below it.

djangobin/django_project/djangobin/admin.py

Visit Add Snippet or Change snippet page again. You should see tags field like this.

To enter the data click on the search-icon beside the input box and a pop-window will open which allows you to select and search through the records.

4. prepopulated_fields – This attribute automatically adds content to the field. It accepts a dictionary mapping field names to the fields it should pre-populate form. It is commonly used to create slugs. For example:

This will pre-populate the slug field from the title field using JavaScript.

Open admin.py and add prepopulated_fields attribute to the TagAdmin class as follows:

djangobin/django_project/djangobin/admin.py

Visit Add tag page (http://localhost:8000/admin/djangobin/tag/add/) and enter some data in the title field. You will that notice the slug field automatically gets populated in real time.

The prepopulated_fields attribute only pre-populate field while adding new a record, it will not pre-populate the field when you update a record.

5. readonly_fields – This attribute makes the fields read-only. It accepts field names as list or tuple.

As things stand, when we create a new snippet, we are required enter data in highlighted_code, slug and hits fields. If you think about it entering data into these field doesn’t really make much sense, no matter whether you are adding a snippet or updating an existing snippet. This is especially true for highlighted_code and slug fields. The former contains the HTML code generated by the Pygments package and the later contains a unique identifier to access the snippets. A better approach would be to make these fields read-only and somehow provide data to them automatically while saving the snippet.

Let’s start by making these fields read-only. Once again open admin.py and add readonly_fields attribute to SnippetAdmin like this:

djangobin/django_project/djangobin/admin.py

Save the file and visit Add snippet (or change snippet) page. You should see a page like this:

Notice that all the three fields are pushed at the end of the page, this happens because Django first displays editable fields followed by read-only fields. We can easily change this behavior using the fields attribute we discussed earlier in this section. Just after readonly_fields attribute in the SnippetAdmin class, add the fields attribute as follows:

djangobin/django_project/djangobin/admin.py

Refresh the Add snippet page and you will see all the field listed in the same order as specified in the fields attribute.

While we are it, let’s make the slug field of Tag model read-only. In the admin.py, comment out prepopulated_fields = {'slug': ('name',)} and then add
readonly_fields attribute to TagAdmin as follows:

djangobin/django_project/djangobin/admin.py

We have made some fields read-only. In the next section, we will see how we can automatically provide data to them.

Before we leave this section, it is important to mention that model fields of type DateField and DateTimeField whose auto_now_add or auto_now parameter is set to True will not appear in Django admin site, even if you add their names to the fields attribute.

In fact, doing so raises a FieldError exception.

Customizing object creation by overriding save() method

The save() method of the models.Model class is called everytime you create or update an object. To customize the object creation we can override the save() method in our model class.

Let’s start by overriding save() method for the Snippet model.

Open models.py and add the save() method after the get_absolute_url() method as follows:

djangobin/django_project/djangobin/models.py

In line 15, the if statement checks whether self.slug exists or not. If it doesn’t then it means that the save() method is called to create the snippet. On the other hand, if self.slug exists, save() method is called to update the snippet. This condition is necessary otherwise, the save() method would change the slug after every update.

In line 17, We call highlight() method of the Snippet model to do the actual highlighting and then we assign its result to the highlighted_code field.

In line 18, we are checking whether self.title contains a value or not. If it doesn’t, we set a default value of "Untitled".

At last, in line 20, we call the overridden save() method to save the result to the database.

After these changes visit Add snippet page and try submitting a snippet or two.

Notice how the data is automatically populated in the highlighted_code, slug, and hits fields. The save() method is run every time you create or update a Snippet object.

You might have noticed that you are still required to submit at-least one tag to create a Snippet object. The Snippet model has many-to-many relationship with the Tag model. We can make the Tag field optional by setting blank=True. Open models.py in djangobin app and update it as follows:

To commit the change create a migration using the makemigrations command:

Then, commit the migration using the migrate command:

Visit Add snippet page again and create a new snippet. You will find that you no longer require submitting tags to create a new snippet.

Let’s now shift our attention to the Tag model.

Just like Snippet objects, we want to create Tag objects without entering any data in the slug field. We have already made slug read-only in the preceding section. The only thing remaining is to override the save() method in the Tag model and set the value of value slug field there. Open model.py file and update it to include the save() method as follows:

In the save() method we are using the slugify() function provided by Django to create the slug from the name field. Recall that slug can only contain letters, numbers, underscores and hyphens. If the value of name field is "enter the dragon" then the slugify() function will return "enter-the-dragon". Also, notice that we are not testing whether slug field contains any value or not because we want the save() method to recreate the slug after every update.

From now on you will be able to create new Tags without entering any value in the slug field.

Changing Field Labels

The form labels in Django admin site uses the field names from the models. If the field name in the model is name then form label will be Name. If label consists of multiple words separated by underscore like pub_date, then form label will be Pub date.

We can explicitly specify the field label using the verbose_name parameter while defining the field in the model class. Open models.py file and add verbose_name to name field in Language model as follows:

djangobin/django_project/djangobin/models.py

To commit the changes use makemigrations and migrate commands as usual.

Visit Add language (or Change language) page to see the changed label.

Adding Help Text to Snippet Form

In Django Models Basics lesson, we have discussed a field option called help_text. If you recall, the help_text option species a string which serve as a description of the field.

Visit Add Snippet (or Change snippet) page and you will get a form like this:

As you can see, the Add snippet form consists of 3 read-only fields: Highlighted Code, Hits and Slug. First time visitor to this page may get confused about how to use this fields. Since we are automatically providing data to these fields, we should explicitly tell users that these fields are read-only and will be populated automatically while saving the snippet.

To add help_text parameter open models.py file in the djangobin app and modify Snippet model as follows:

djangobin/django_project/djangobin/models.py

Once again run makemigrations and migrate command to commit changes. Refresh the Add snippet (or Change snippet) page to see the help text:

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