The same features can be developed quickly for Android and iOS applications and released simultaneously. Django is a popular framework for developing social media platforms such as Pinterest, Instagram, and Reddit. It has utilities to deal with massive amounts of data and handle multiple user interactions every second. Pinterest has around million active users, so it is important to have a high-performing website that has speed and scalability. Pinterest uses Django to handle thousands of users simultaneously and enable managing followers, boards, pins, and posts.

Using the cloud, you can access your files anywhere and from any device. Dropbox is the most famous and popular cloud storage application for documents, videos, graphics, and photos.

Python was used to build the backend and client software of Dropbox. Using Django, developers were able to quickly add features such as user history access, version control option, account synchronization across multiple devices, and file-sharing services.

The Onion is another popular example of a Django website. A satirical newspaper that reports on world news in a humorous manner, The Onion developed an online website version in Since then, all publications, designs, articles have been published online. The Python website was so successful that the company ceased print publishing in Today, it is one of the most famous sources of news. Django was used for developing all the features and functionalities of the site.

Spotify, working on multiple devices, allows users to download and listen to music. It is a famous platform, with many artists releasing their albums directly on it. The Django framework was the perfect choice because of the need for Fast backend and machine learning options.

Disqus is a website comment plugin service that enables users to engage in the comment box. One of the most popular comment plugin options of today, Disqus offers vast customizations using Django. With the capability of handling thousands of users at a time, the development team at Disqus used Django for its scalability, maintainability, and high-performance speeds. The Disqus engineering team, along with using Django extensively in their platform, also developed Sentry, an internal tool for monitoring errors, bugs, and app crashes.

Sentry is open-source software that various companies and organizations use for error checking. Sentry supports more than 30, companies and their projects, including Instagram, Reddit, Prezi, and DataDog. Since security is highly important in Django, Python is often used along with Django in government applications and healthcare websites. The Django website manages more than a million users on a daily basis. Although relatively simple in its design, the NASA website supports high-definition videos of space and most importantly meets the high-security requirements of the company.

These are some examples of popular websites built with Django that showcase its many features. This is best illustrated with an example:.

This is handy for when you are paginating data or want to return the Top 10, say, of a QuerySet. This is because Django creates a primary key automatically when it adds a record to the database. Figure 4. To update records, you change the instance data and call the save method again.

Each subsequent call to the save method will update the record:. To ensure records are updated in the most efficient manner possible, use the update method. Rewriting the above process to use the update method, you get:. You can also use update to modify multiple records.

The return value tells you that update has changed two records in the database. If you check the database, you will also see that all events at the bar have moved to the casino Figure 4. The return value for the delete method lists the total number of records affected one in this example , a dictionary listing the tables affected by the delete operation, and the number of records deleted in each table. To prevent accidental deletion of all the data in a table, Django requires you to use the all method explicitly to delete everything in a table.

This is primarily due to well-established database design best-practice. If you were only saving the venue name in the database, you could get away with repeating the name of the venue multiple times in your database records.

But what about if you wanted to save more information for the venue? Your venue records should also include an address, telephone number, website address and email.

If you add these fields to your events table, you can see that you will end up with a lot of repeated information, not to mention the nightmare of ensuring you update all records if some venue information changes. Database normalization is the process of designing your tables to minimize or eliminate data repetition. In simple terms, normalization is keeping related data in separate tables and linking tables via relationships hence the name relational database.

So, as you would expect, Django makes creating relationships between tables of related information simple. With our venue example, it would be good practice to have all the venue information in one table, and link to that information from the event table. We create this link in Django with a foreign key. Multiple events linking to one venue record is an example of a many-to-one relationship in relational database parlance.

Looking at the relationship in the opposite direction, we get a one-to-many relationship , i. Django provides QuerySet methods for navigating relationships in both directions—from one to many, and from many to one—as you will see shortly. There is one other common database relationship that we need to explore, and that is the many-to-many relationship. An excellent example of a many-to-many relationship is the list of people who are going to an event.

Each event can have many attendees, and each attendee can go to multiple events. To update a non-relation field, provide the new value as a constant. To update ForeignKey fields, set the new value to be the new model instance you want to point to. The update method is applied instantly and returns the number of rows matched by the query which may not be equal to the number of rows updated if some rows already have the new value.

Be aware that the update method is converted directly to an SQL statement. It is a bulk operation for direct updates. Loop over them and call save :. Calls to update can also use F expressions to update one field based on the value of another field in the model. This is especially useful for incrementing counters based upon their current value. For example, to increment the pingback count for every entry in the blog:. If you attempt to introduce a join with an F object, a FieldError will be raised:.

When you define a relationship in a model i. Using the models at the top of this page, for example, an Entry object e can get its associated Blog object by accessing the blog attribute: e.

Behind the scenes, this functionality is implemented by Python descriptors. All examples in this section use the sample Blog , Author and Entry models defined at the top of this page. If a model has a ForeignKey , instances of that model will have access to the related foreign object via an attribute of the model. You can get and set via a foreign-key attribute. Forward access to one-to-many relationships is cached the first time the related object is accessed.

Subsequent accesses to the foreign key on the same object instance are cached. If a model has a ForeignKey , instances of the foreign-key model will have access to a Manager that returns all instances of the first model.

By default the RelatedManager used for reverse relations is a subclass of the default manager for that model. If you would like to specify a different manager for a given query you can use the following syntax:. A synopsis of each is below, and complete details can be found in the related objects reference.

To assign the members of a related set, use the set method with an iterable of object instances. For example, if e1 and e2 are Entry instances:. If the clear method is not available, all objects in the iterable will be added without removing any existing elements. Every addition, creation and deletion is immediately and automatically saved to the database.

Both ends of a many-to-many relationship get automatic API access to the other end. Another difference from one-to-many relationships is that in addition to model instances, the add , set , and remove methods on many-to-many relationships accept primary key values. For example, if e1 and e2 are Entry instances, then these set calls work identically:.

One-to-one relationships are very similar to many-to-one relationships. If you define a OneToOneField on your model, instances of that model will have access to the related object via an attribute of the model. The related model in a one-to-one relationship also has access to a Manager object, but that Manager represents a single object, rather than a collection of objects:.

If no object has been assigned to this relationship, Django will raise a DoesNotExist exception. Instances can be assigned to the reverse relationship in the same way as you would assign the forward relationship:.

Other object-relational mappers require you to define relationships on both sides. The answer lies in the app registry. Whenever a new model class is created, Django adds backward-relationships to any related models. Otherwise, backwards relations may not work properly. Queries involving related objects follow the same rules as queries involving normal value fields.

When specifying the value for a query to match, you may use either an object instance itself, or the primary key value for the object. Offline Django 3. Django is a registered trademark of the Django Software Foundation. Django The web framework for perfectionists with deadlines. Documentation Search: Search. Getting Help el es fr id it ja ko pl pt-br zh-hans Language: en 1. See also save takes a number of advanced options not described here.

Manager object at AttributeError: "Manager isn't accessible via Blog instances. For example, to get a QuerySet of blog entries from the year , use filter like so: Entry. How this is possible Python has the ability to define functions that accept arbitrary name-value arguments whose names and values are evaluated at runtime.

Note The behavior of filter for queries that span multi-value relationships, as described above, is not implemented equivalently for exclude. Changed in Django 3. Note Simply printing the queryset will not populate the cache. To demonstrate, we will use the following example model: from django. Note The lookup examples given above implicitly use the exact lookup. Note Due to the way in which key-path queries work, exclude and filter are not guaranteed to produce exhaustive sets.

Warning Since any string could be a key in a JSON object, any lookup other than those listed below will be interpreted as a key lookup. The field will always output a list of countries in this mode. For example:. An object used to represent a country, instantiated with a two character country code, three character code, or numeric code. It can be compared to other objects as if it was a string containing the country code and when evaluated as text, returns the country code.

Output the css classes needed to display an HTML element as the correct flag from within a single sprite image that contains all flags. For multiple flag resolutions, use sprite-hq. You might also want to consider using aria-label for better accessibility:.

A widget is included that can show the flag image after the select box updated with JavaScript when the selection changes. Pass a layout text argument to the widget to change the positioning of the flag and widget.

The default layout is:. You can also use the CountrySelectWidget as the widget for this field if you want the flag image after the select box. If you have your country code stored in a different place than a CountryField you can use the template tag to get a Country object and have access to all of its properties:.

The values can also use a more complex dictionary format. By default, these initial countries are not repeated again in the alphanumerically sorted list. It defaults to:. To customize an individual field, rather than rely on project level settings, create a Countries subclass which overrides settings.

Then just reference this class in a field. For example, this CountryField uses a custom country list that only includes the G8 countries:. Other Python packages can add attributes to the Country object by using entry points in their setup script. The entry point name phone will be the new attribute name on the Country object.

Use the following mixin with your model serializer:. This mixin handles both standard and multi-choice country fields. For lower level use or when not dealing with model fields , you can use the included CountryField serializer field. You can optionally instantiate the field with the countries argument to specify a custom Countries instance.

By default, the field will output just the country code. A Country graphene object type is included that can be used when generating your schema. This log shows interesting changes that happen for each version, latest versions first. It can be assumed that translations have been updated each release, and any new translations added. May 11, May 9, Mar 17, Dec 5, Aug 18, Mar 26, Mar 20, Feb 27, Sep 11,