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Define and set table field

Not all of them are relevant for every field. "length" is relevant only for fields of type "string". "uploadfield" and "authorize" are relevant only for fields of type "upload". "ondelete" is relevant only for fields of type "reference" and "upload". See below for more information.






















Field(fieldname, 

type='string',
length=None,
default=None,
required=False,
requires='<default>',
ondelete='CASCADE',
notnull=False, unique=False,
uploadfield=True,
widget=None,
label=None,
comment=None,
writable=True,
readable=True,
update=None,
authorize=None,
autodelete=False,
represent=None,
compute=None,
uploadfolder=None,
uploadseparate=None,uploadfs=None,
rname=None)

Attributes / Arguments

length sets the maximum length of a "string", "password" or "upload" field. If length is not specified a default value is used but the default value is not guaranteed to be backward compatible. To avoid unwanted migrations on upgrades, we recommend that you always specify the length for string, password and upload fields.

default sets the default value for the field.
The default value is used when performing an insert if a value is not explicitly specified. It is also used to pre-populate forms built from the table using SQLFORM.
Note, rather than being a fixed value, the default can instead be a function (including a lambda function) that returns a value of the appropriate type for the field. In that case, the function is called once for each record inserted, even when multiple records are inserted in a single transaction.

required tells the DAL that no insert should be allowed on this table if a value for this field is not explicitly specified.

requires is a validator or a list of validators. This is not used by the DAL, but it is used by SQLFORM. The default validators for the given types are shown in the next section.

Notice that requires=... is enforced at the level of forms, required=True is enforced at the level of the DAL (insert), while notnull, unique and ondelete are enforced at the level of the database. While they sometimes may seem redundant, it is important to maintain the distinction when programming with the DAL.

uploadfolder while the default is None, most DB adapters will default to uploading files into os.path.join(request.folder, 'uploads'). MongoAdapter does not seem to be doing so at present.

rname provides the field was a "real name", a name for the field known to the database adapter; when the field is used, it is the rname value which is sent to the database. The web2py name for the field is then effectively an alias.

ondelete translates into the "ON DELETE" SQL statement. By default it is set to "CASCADE". This tells the database that when it deletes a record, it should also delete all records that refer to it. To disable this feature, set ondelete to "NO ACTION" or "SET NULL".

ondelete='CASCADE'


notnull=True translates into the "NOT NULL" SQL statement. It prevents the database from inserting null values for the field.

Translates into the "UNIQUE" SQL statement and it makes sure that values of this field are unique within the table. It is enforced at the database level.

uploadfield applies only to fields of type "upload". A field of type "upload" stores the name of a file saved somewhere else, by default on the filesystem under the application "uploads/" folder.
If uploadfield is set to True, then the file is stored in a blob field within the same table and the value of uploadfield is the name of the blob field.

uploadfield=True

Defaults to the application's "uploads/" folder. If set to a different path, files will uploaded to a different folder.

Field(...,uploadfolder=os.path.join(request.folder,'static/temp'))

# will upload files to the "web2py/applications/myapp/static/temp" folder.

uploadseparate if set to True will upload files under different subfolders of the uploadfolder folder. This is optimized to avoid too many files under the same folder/subfolder.

ATTENTION: You cannot change the value of uploadseparate from True to False without breaking links to existing uploads. web2py either uses the separate subfolders or it does not. Changing the behavior after files have been uploaded will prevent web2py from being able to retrieve those files. If this happens it is possible to move files and fix the problem.

uploadfs allows you specify a different file system where to upload files, including an Amazon S3 storage or a remote SFTP storage. This option requires PyFileSystem installed. uploadfs must point to PyFileSystem. uploadfs

widget must be one of the available widget objects, including custom widgets, for example: SQLFORM.widgets.string.widget. A list of available widgets will be discussed later. Each field type has a default widget.

label is a string (or a helper or something that can be serialized to a string) that contains the label to be used for this field in auto-generated forms.

comment is a string (or a helper or something that can be serialized to a string) that contains a comment associated with this field, and will be displayed to the right of the input field in the autogenerated forms.

writable declares whether a field is writable in forms.

readable declares whether a field is readable in forms. If a field is neither readable nor writable, it will not be displayed in create and update forms.

update contains the default value for this field when the record is updated.

compute is an optional function. If a record is inserted or updated, the compute function will be executed and the field will be populated with the function result. The record is passed to the compute function as a dict, and the dict will not include the current value of that, or any other compute field.

authorize can be used to require access control on the corresponding field, for "upload" fields only.

autodelete determines if the corresponding uploaded file should be deleted when the record referencing the file is deleted. For "upload" fields only. However, records deleted by the database itself due to a CASCADE operation will not trigger web2py's autodelete. The web2py Google group has workaround discussions.

autodelete=False

represent can be None or can point to a function that takes a field value and returns an alternate representation for the field value.



db.mytable.name.represent = lambda name,row: name.capitalize()
db.mytable.other_id.represent = lambda id,row: row.myfield
db.mytable.some_uploadfield.represent = lambda value,row:     A('get it', _href=URL('download', args=value))


Related References


Examples

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Sources / Reference

" Web2py Book - Chapter 6 Database Abstraction Level" is licensed under Creative Common License BY-NC-ND 3.0


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