Django Models – Data Field Type
Fields are a crucial part of a relational database storing data. Each field determines a data type that can store a specific type of data. Django provides several field types. A field type is written in PascalCase. Some field types require specific arguments. For example, max_length is required for CharField. In this section, we'll explain key data field types.
Field types for strings
CharField
This field type is one of the most frequently used field types. This field can store small-to-large strings.
Key Arguments
max_length: Required argument. Without this argument, Django gives an error message. Using this argument, you can specify the maximum length of the field.
TextField
This field is used to store a large text.
Key Arguments
max_length: Optional argument. Using this argument, you can specify the maximum length of the field.
SlugField
This field is used to store strings of alphabets, numbers, underscores, or hyphens, which are generally used in URLs.
Key Arguments
max_length: Optional argument. If you don't specifymax_length, a default of50is used.
URLField
This field is used to store a URL validated by a URL validator.
Key Arguments
max_length: Optional argument. If you don't specifymax_length, a default of200is used.
Field types for Logic
BooleanField
This field is used to store a True or False value. In a form input, this field usually becomes a check box input.
3. Field types for Numbers
IntegerField
This field is used to store an integer. According to the Django documentation, Values from -2147483648 to 2147483647 are safe in all databases supported by Django.
PositiveIntegerField
This field is used to store a positive integer or zero value. According to the Django documentation, Values from 0 to 2147483647 are safe in all databases supported by Django.
FloatField
This field is used to store a floating-point number represented in Python by a float instance.
DecimalField
This field is used to store a fixed-precision decimal number, represented in Python by a decimal instance.
Key Arguments
decimal_places: Required argument. Using this argument, you can specify the number of decimal places to store the number.max_digits: Required argument. Using this argument, you can specify the maximum number of digits allowed in the number. This number must be greater than or equal todecimal_places.
Note: Floating-point number vs. decimal number
Floating-point numbers in FloatField are handled in binary numbers. In some cases, calculations using this field may not be very accurate, but the data processing speed tends to be faster.
Decimal numbers in DecimalField are handled in decimal numbers. Calculations using this field are more accurate, but the data processing speed tends to be slower.
AutoField
This field is used to store an integer that automatically increments. This type of field is used for primary key IDs. Django gives each model an auto-incrementing primary key by default, so you usually won’t need to use this field type.
4. Field types for Date & Time
DateField
This field is used to store a date, represented in Python by a datetime.date instance.
Key Arguments
auto_now_add: Optional argument. This option is often used for thecreated_atcolumn in a database table. When this argument is True, the value in the field is set with the current date when the record object is first created.auto_now: Optional argument. This option is often used for theupdated_atcolumn in a database table. When this argument is True, the value in the field is updated with the current date when the record object is updated and saved.
DateTimeField
This field is used to store date and time, represented in Python by a datetime.datetime instance.
Key Arguments
The auto_now_add and auto_now options are optional arguments for this field type.
TimeField
This field is used to store time, represented in Python by a datetime.time instance.
Key Arguments
The auto_now_add and auto_now options are optional arguments for this field type.
Tips: Editable timestamp
When auto_now_add or auto_now argument is True, you won't be able to modify the field (DateField or DateTimeField) as it is used for the auto-generated timestamp. If you want to modify the field, you need to try another implementation using imported modules like the ones below.
- For DateField:
default=date.today- fromdatetime.date.today() - For DateTimeField:
default=timezone.now- fromdjango.utils.timezone.now()
We'll explain this in the later section of this chapter.
5. Field types for Files
ImageField
This field is used to store image file information. The Pillow library is required to use this field type.
Key Arguments
upload_to: Required argument. Using this argument, you can specify the location (subdirectory) to save an uploaded image file. This argument only specifies a subdirectory path. The main directory for uploading files is defined in the settings.py file –MEDIA_ROOTandMEDIA_URL. If you are not creating a subdirectory, you can use a blank for the option value (upload_to=' '). We'll explain how to edit settings.py for media file handling later.height_field: Optional argument. Using this argument, you can specify the height of the image.width_field: Optional argument. Using this argument, you can specify the width of the image.
Note: Pillow
Pillow is a Python Imaging Library (PIL) fork that adds image processing capabilities to the Python interpreter. When you use ImageField in Django, you need this library in your app.
FileField
This field is used to store file information. Using this field type, you can handle other-than-image files.
Key Arguments
There are optional arguments for this field type, such as upload_to and storage.
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