.. highlight:: rst
.. index:: view-mixin ; Index


.. _ref-view-mixin:

==========
View Mixin
==========

**Overview**

This mixin is designed to enhance Django class-based views (CBVs) that work with forms specifically related to tagging functionality. Its primary purpose is to streamline the process of passing relevant arguments directly to the initialization (`__init__`) method of your custom `TagMeModelForm`.  This ensures that the form has all the necessary information to render and handle tagged fields correctly.

**Key Functionality**

* **Inheritance:**
    - It inherits from Django's `FormMixin`, which is a common base class for CBVs that work with forms. This gives it access to the core form handling methods in Django views.
* **Custom `get_form` Method:**
    - It overrides the standard `get_form` method. This is the method Django calls to instantiate the form for the view.
    - It ensures that the form class used is a subclass of `TagMeModelFormMixin`. This is essential because the `TagMeModelFormMixin` contains the logic for handling tagged fields. If the form class is not compatible, it raises an `ImproperlyConfigured` exception to prevent unexpected behavior.
    - It constructs a dictionary of keyword arguments (`form_kwargs`) to pass to the form's `__init__` method.
    - It checks if the `user` is already in `form_kwargs` (it may have been added by other mixins or the view itself). If not, it adds the current `request.user` to `form_kwargs`.
    - It crucially adds the `model_verbose_name` (the human-readable name of the model associated with the form) to `form_kwargs`. This is the piece of information that the `TagMeModelFormMixin` needs to identify the correct model and its tagged fields.

**Simplified Diagram (Graphviz)**

.. graphviz::


  digraph {
    rankdir=LR;

    TagMeViewMixin [shape=box, style=filled, fillcolor=lightblue, label="TagMeViewMixin"];
    FormMixin [shape=box, style=filled, fillcolor=lightgray, label="FormMixin (Django)"];
    TagMeModelFormMixin [shape=box, style=filled, fillcolor=lightgreen, label="TagMeModelFormMixin"];

    TagMeViewMixin -> FormMixin [label="Inherits", arrowhead=empty];
    TagMeViewMixin -> TagMeModelFormMixin [label="Works with", arrowhead=vee, style=dashed];
  }

**Key Points**

* **Integration with `TagMeModelFormMixin`:**  The core purpose of `TagMeViewMixin` is to seamlessly pass information to the `TagMeModelFormMixin`, specifically the user and the model's verbose name. This allows the form mixin to handle tagged fields correctly.
* **Customization Point:** If you have additional arguments that need to be passed to the form, you can easily extend this mixin's `get_form` method to include them.
* **Error Handling:** It includes a check to ensure that the form used with this mixin is compatible, raising an exception if it's not, to avoid unexpected behavior.




