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Django - Model Fields

Django - Model Fields

Model Fields

Model fields:
- the columns name of the mapped table.
- The fields name should not be python reserve words like clean, save or delete etc.
Django provides various built-in fields types:
- ref: https://docs.djangoproject.com/en/4.2/ref/models/fields/#field-types
Primary key:

Field	Description	Widget
`AutoField()`	An IntegerField that automatically increments.
`BigAutoField()`	A 64-bit integer that automatically increments.
`UUIDField()`	A field for storing universally unique identifiers.

Boolean:

Field	Description	Widget
`BooleanField()`	A true/false field.	`CheckboxInput`

Integer:

Field	Description	Widget
`BigIntegerField()`	A 64-bit integer	`NumberInput`
`IntegerField()`	An integer field	`NumberInput`
`SmallIntegerField()`	Like an IntegerField	`NumberInput`
`PositiveIntegerField()`	An integer field for zero or positive	`NumberInput`

Decimal:

Field	Description	Widget
`DecimalField(max_digits=None, decimal_places=None)`	A fixed-precision decimal number	`NumberInput`
`FloatField()`	A floating-point number field	`NumberInput`

String:

Field	Description	Widget
`CharField(max_length=None)`	A string field, for small- to large-sized strings.	`TextInput`
`EmailField(max_length=254)`	A string field for email	`TextInput`
`TextField()`	A large text field.	`Textarea`
`GenericIPAddressField()`	An IPv4 or IPv6 address string	`TextInput`
`URLField(max_length=200)`	A CharField for a URL	`URLInput`
`SlugField(max_length=50)`	A field for only letters, numbers, underscores or hyphens
`FilePathField()`	Choices limited to the filenames in a certain directory

Date:

Field	Description	Widget
`DateTimeField((auto_now=False, auto_now_add=False)`	A date and time field	`DateTimeInput`
`DateField(auto_now=False, auto_now_add=False)`	A date field	`DateInput`
`TimeField(auto_now=False, auto_now_add=False)`	A time field.	`TimeInput`
`DurationField()`	Periods of time.

Data:

Field	Description
`BinaryField()`	A field to store raw binary data.
`JSONField()`	A field to store JSON encoded data.

File:

Field	Description	Widget
`FileField()`	A file-upload field	`ClearableFileInput.`
`ImageField()`	A image-upload field	`ClearableFileInput`

Relationship fields

Field	Description
`ForeignKey(to, on_delete)`	A many-to-one relationship.
`ManyToManyField(to)`	A many-to-many relationship.
`OneToOneField(to, on_delete, parent_link=False)`	A one-to-one relationship.

Field options

a certain set of field-specific arguments
- ref: https://docs.djangoproject.com/en/4.2/ref/models/fields/#field-options
Constraint

Option	Description	Default
`primary_key`	primary key	NA
`null`	empty values	`False`
`blank`	allowed to be blank	`False`
`choices`	A choice sequence	NA
`default`	default value	NA
`unique`	unique values	NA
`unique_for_date`	unique for date value	NA
`unique_for_month`	unique for month value	NA
`unique_for_year`	unique for year value	NA

Meta

Option	Description	Default
`db_column`	column name
`verbose_name`	A human-readable field name
`db_comment`	comment on column
`db_index`	a database index
`db_tablespace`	tablespace name
`editable`	editability	`True`
`error_messages`	error messages
`help_text`	“help” text for widget
`validators`	A list of validators to run

Example: Upload MP3 Files Using FileField

HTML:

<!-- 
sets the value of enctype attribute: 
  assigns the uploaded file to request.FILE. Otherwise, the file will not be uploaded.
-->
<form
  id="form"
  action="__'music_test_upload'__"
  method="post"
  enctype="multipart/form-data"
>
  __csrf_token__

  <input id="music_name" name="music_name" class="form-control col-md-6 my-2" />

  <!-- 
sets name attribute as 'upload_file':
  the uploaded file can be achieved by the request.FILE["upload_file"]`
 -->
  <input
    id="file"
    type="file"
    class="form-control col-md-6 my-2"
    name="upload_file"
  />
  <button id="btn" class="btn btn-primary" type="submit">submit</button>
</form>

model_py

# the musice class represents the uploaded file in database.
# the FileField is actually the path storing the uploaded file.
# the 'upload_to' attribute:
#   the directory storing files.
#   default: ""
#   actual value is settings.MEDIA_ROOT.
#   example:  `upload_to='music/'` means the directory is `settings.MEDIA_ROOT/music/`。

class Music(models.Model):
    name = models.CharField(max_length=255)
    description = models.CharField(max_length=255, blank=True)
    file = models.FileField(upload_to='music/')

view.py

def music_test_upload(request):
    ''' the view handles upload file page and stores the uploaded file '''
    context = {}
    html = "AppMusic/test.html"
    data = {}

    #when the submit method is post and a file has been submited.
    if request.method == 'POST' and request.FILES['upload_file']:
        music_name = request.POST["music_name"]
        upload_file = request.FILES['upload_file']    # get the uploaed file
        upload_file.name = music_name + ".mp3"        # modify the file name

        # kwag dict for Music model
        submit_data ={}
        submit_data["name"] = music_name
        submit_data["file"] = upload_file   # assign the uploaded file to the file field, whose type is FileField.

        try:
            new_music = Music(**submit_data)
            new_music.save()    # the uploaded file will be save into the target directory.
            print(new_music.file.url)
            data["success"] = "Successfully create a new record !"                 # response msg: success
        except Exception as error:                      # error
            data["error"] = str(error)                  # response msg: error

        context['data'] = data

    return render(request,html,context)

# Note:
# `new_music.file.url`：`FileField`类型的`url`属性是访问上存文件的url。该属性值是：`settings.MEDIA_URL` + `FileField`的`upload_to`属性 + `upload_file.name`。
# 当在前段需要引用上存文件时，可以直接使用``
# 注意：上存的文件与已存在的文件重名，django会自动修改新上存文件的文件名并自动记录在`FileField`字段中。

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