Adding new download formats

While the Aristotle-MDR framework has a PDF download extension, it may be desired to download metadata stored within a registry in a variety of download formats. Rather than include these within the Aristotle-MDR core codebase, additional download formats can be developed included via the download API.

Downloads architecture

There are two parts to the downloads module

  • Django views will serve and it will start a job with Celery that will yield a download file asynchronously.
  • Celery will have the tasks registered from the downloads class. Celery worker will add the file to a redis cache.

Creating a download module

A download module is a specialised class, that sub-classes aristotle_mdr.downloader.Downloader and provides an appropriate get_download_config and download or get_bulk_download_config and bulk_download methods.

A download module is just a Django app that includes a specific set of files for generating downloads. The only files required in your app are:

  • - to declare the app as a python module
  • - where your download classes will be stored

Other modules can be written, for example a download module may define models for recording a number of times an item is downloaded.

Writing a metadata_register

Your downloader class must contain a register of download types and the metadata concept types which this module provides downloads for. This takes one of the following forms which define which concepts can be downloaded as in the output format:

class CSVExample(Downloader):
    download_type = "csv"
    metadata_register = {'aristotle_mdr': ['valuedomain']}

class XLSExample(Downloader):
    download_type = "xls"
    metadata_register = {'aristotle_mdr': ['__all__']}

class PDFExample(Downloader):
    download_type = "pdf"
    metadata_register = '__template__'

class TXTExample(Downloader):
    download_type = "txt"
    metadata_register = '__all__'

Describing these options, these classes specifies the following downloads:

  • csv provides downloads for Value Domains in the Aristotle-MDR module
  • xls provides downloads for all metadata types in the Aristotle-MDR module
  • pdf provides downloads for items in all modules, only if they have a download template
  • txt provides downloads for all metadata types in all modules

Each download class must also define a class method with the following signature:

def get_download_config(cls, request, iid):
    return properties, iid

This is a download config which creates the json serializable properties for the request. This will ensure that the task can be passed on to Celery, which requires the objects to be json serializable.

The arguments are

  • request - the request object that was used to call the download view. The current user trying to download the item can be gotten by calling request.user.
  • iid - This is the id of the item that needs to be downloaded

The return arguments are:

  • properties - This will save essential information like user email(can be used by celery to get user object) and title of the document(to be displayed to the user while the download is generated).
  • iid - This would be same as the input argument in most cases. It is present to manipulate the iid if required.

Each download class must also define a static method with the following signature:

def download(properties, iid):

A shared task is a celery worker hook which will register this function as a celery task This is called from Aristotle-MDR when it catches a download type that has been registered for this module. The arguments are:

  • properties - This will contain all the variables required by celery task to prepare the download.
  • iid - the id of the item to be downloaded, to be retrieved from the database.

Note: If a download method is called the user has been verified to have permissions to view the requested item only. Permissions for other items will have to be checked within the download method.

The get_bulk_download_config and bulk_download method works in same fashion as get_download_config and download respectively.

For more information see the Downloader class below:

class aristotle_mdr.downloader.Downloader(item_ids: typing.List[int], user_id: typing.Union[int, NoneType], options: typing.Dict[str, typing.Any] = {}, override_bulk: bool = False)[source]

Base class used by all downloaders Subclasses must override the create_file method

Required class properties:

  • description: a description of the downloader type
  • download_type: the extension or name of the download to support
  • icon_class: the font-awesome class
  • metadata_register: can be one of:
    • a dictionary with keys corresponding to django app labels and values as lists of models within that app the downloader supports
    • the string “__all__” indicating the downloader supports all metadata types
    • the string “__template__” indicating the downloader supports any metadata type with a matching download template
create_file() → django.core.files.base.File[source]

Create the file object, should be overwritten by subclasses See below for examples

download() → str[source]

Get the url for this downloads file, creating it if necessary

classmethod get_class_info() → typing.Dict[str, typing.Any][source]

Used as context instead of passing classes to templates


Gets a storage class object (use media to get default media class instead of dl class)

retrieve_file(filename: str) → typing.Union[str, NoneType][source]

Use default storage class to retrieve file if it exists

store_file(filename: str, content: django.core.files.base.File) → str[source]

Use default storage class to store file

How the download view works