Django writing custom fields



Again, these are just short descriptions of the most common field options. As with ForeignKey , you can also create recursive relationships an object with a many-to-many relationship to itself and relationships to models not yet defined.

Meta appears in will be the one that is used; for example, this means that if multiple parents contain a Meta class, only the first one is going to be used, and all others will be ignored.

A proxy model must inherit from exactly one non-abstract model class. The CommonInfo model cannot be used as a normal Django model, since it is an abstract base class. You do this by creating instances of the intermediate model:. You can create, delete and update instances of the proxy model and all the data will be saved as if you were using the original non-proxied model.

Continuing our example from above, you could change the default manager used when you query the Person model like this: See the Many-to-many relationship model example for a full example.

The last method in this example is a property. It uses the quoting syntax of your particular database engine. Create an abstract class for the new manager. Once you have MytypeField , you can use it in any model, just like any other Field type:. The better way of doing this would be to make the parameter specifiable at run time — i.

If one of the existing model fields cannot be used to fit your purposes, or if you wish to take advantage of some less common database column types, you can create your own field class. You can then put extra fields on the intermediate model. For our musician example, the code would look something like this: For example see save for documentation of the parameters it accepts: In this example, the verbose name is "person's first name": Here are a couple of tips to make things go more smoothly: In particular, any new instances of Person will also be accessible through MyPerson , and vice-versa:.

Another way to access the same information is by querying the many-to-many reverse relationship from a Person object:. Django uses this in its admin interface, and any time it needs to figure out a URL for an object.

The trick is to tell Django how to handle saving and loading such an object. Normal Python attributes can be overridden if you wish. If you do override this method, you must return the value of the attribute at the end.

Our HandField accepts most of the standard field options see the list below , but we ensure it has a fixed length, since it only needs to hold 52 card values plus their suits; characters in total.

However, there are a few limited cases where the child inherits behavior from the parent: The column type, which tells the database what kind of data to store e. See the field documentation for examples and details. It is not a way to replace the Person or any other model everywhere with something of your own creation. If True , this field is the primary key for the model. Full coverage of creating your own fields is provided in Writing custom model fields. Fields are specified by class attributes.

This sets things up so that the proxy model is an exact copy of the storage structure of the original model when data is saved. This allows you to use backend-specific conversion logic if it is required. This is the class that knows how to convert your first class back and forth between its permanent storage form and the Python form. Django will, from time to time, extend the capabilities of built-in model methods, adding new arguments. For example, if the models for your application live in the module myapp.

IntegerField 'pass' is a reserved word! The first class is the Python object that your users will manipulate. This tells Django how to calculate the URL for an object. The model instance reference has a complete list of methods automatically given to each model. Django offers ways to define the three most common types of database relationships: Keep in mind that normal Python name resolution rules apply. For example, the description for CharField is: If not, you should subclass the Field class, from which everything is descended.

For many uses, this type of model inheritance will be exactly what you want. The remove method is disabled for similar reasons. You might only be wanting to take advantage of custom database column types and deal with the data as standard Python types in your models; strings, or floats, for example.

None are required, and adding class Meta to a model is completely optional. Once a subclass of File is created, the new FileField subclass must be told to use it. They are always in sync with the parent model since they directly inherit its fields and managers. The default HTML widget to use when rendering a form field e.

To do this simply provide descriptive text in a description class attribute of your custom field. If you forget, Django will raise a validation error. All of the fields of Place will also be available in Restaurant , although the data will reside in a different database table. Here are a couple of tips to make things go more smoothly:.

However, there is a lot of detail about the membership that you might want to collect, such as the date at which the person joined the group.