# Exclude-By Primary Author

## Example Overview

- **Objective**: This example showcases how to dynamically exclude certain options in one field based on the selection in another field using `django_tomselect`. Specifically, the "Contributing Authors" field excludes the "Primary Author" selection to prevent redundant choices. Also, if no Primary Author is selected, the Contributing Authors field will remain empty.
  - **Problem Solved**: Maintaining data integrity and logical consistency.

- **Use Case**:
  - Assigning roles to users where overlapping responsibilities are invalid (e.g., primary and secondary roles in a project).
  - Preventing duplicate selections in multi-step forms or hierarchical data inputs.

**Visual Examples**

![Screenshot: Exclude-By Primary Author](https://raw.githubusercontent.com/OmenApps/django-tomselect/refs/heads/main/docs/images/exclude-by-primary-author.png)


## Key Code Segments

### Forms
The form uses `TomSelectModelChoiceField` for the "Primary Author" and `TomSelectModelMultipleChoiceField` for "Contributing Authors". The `exclude_by` parameter ensures contributing authors exclude the selected primary author.

:::{admonition} Form Definition
:class: dropdown

```python
class ExcludeByPrimaryAuthorForm(forms.Form):
    """Form with dependent fields demonstrating exclude_by functionality."""

    primary_author = TomSelectModelChoiceField(
        config=TomSelectConfig(
            url="autocomplete-author",
            value_field="id",
            label_field="name",
            css_framework="bootstrap5",
        ),
    )

    contributing_authors = TomSelectModelMultipleChoiceField(
        config=TomSelectConfig(
            url="autocomplete-author",
            value_field="id",
            label_field="name",
            exclude_by=("primary_author", "id"),
            css_framework="bootstrap5",
            placeholder=_("Select contributing authors..."),
            highlight=True,
            max_items=None,
            plugin_remove_button=PluginRemoveButton(),
        ),
        attrs={"class": "form-control mb-3"},
        required=False,
    )
```
:::

**Explanation**:
- The `exclude_by` parameter in the `contributing_authors` field ensures that any selected "Primary Author" is removed from the available options in the "Contributing Authors" field.
- The `RemoveButton` plugin improves user interaction by enabling quick removal of selected contributing authors.

### Templates
The form is rendered in the `exclude_by.html` template, highlighting the exclusion mechanism between the two fields.

:::{admonition} Template Code
:class: dropdown

```html
{% extends 'example/base_with_bootstrap5.html' %}

{% block extra_header %}
    {{ form.media }}
    <style>
        .helptext {
            font-size: 10px;
            color: #757575;
        }
    </style>
{% endblock %}

{% block content %}
    <div class="card">
        <div class="card-header">
            <h2>Exclude-By Primary Author Demo</h2>
        </div>
        <div class="card-body">
            <div class="pb-5">
                This page demonstrates how to exclude available options based on the selected value of another field.
                In this case, the options for Contributing Author include all except the selected Primary Author.
            </div>
            <form>
                {% csrf_token %}
                {{ form.as_div }}
            </form>
        </div>
    </div>
{% endblock %}
```
:::

**Key Elements**:
- Bootstrap 5 for clean and modern styling.
- The exclusion logic is visually reflected in the dropdowns as selections are made.

### Autocomplete Views
The `autocomplete-author` endpoint serves data for both fields, ensuring proper exclusion logic based on the `exclude_by` parameter.

- We override the `get_queryset` method to filter authors based on the selected magazine (if any).
- The `hook_prepare_results` method adds a formatted name to each author result for better readability.

:::{admonition} Autocomplete View
:class: dropdown

```python
class AuthorAutocompleteView(AutocompleteModelView):
    """Autocomplete view for Author model with annotations and advanced searching."""

    model = Author
    search_lookups = [
        "name__icontains",
        "bio__icontains",
    ]
    ordering = ["name"]
    page_size = 20
    value_fields = ["id", "name", "bio", "article_count", "active_articles"]

    list_url = "author-list"
    create_url = "author-create"
    update_url = "author-update"
    delete_url = "author-delete"

    skip_authorization = True

    def get_queryset(self):
        """Return a queryset of authors with article count annotations.

        Annotates:
        - Total number of articles by author
        - Number of active articles by author
        - Articles by magazine (as a string list)
        """
        queryset = super().get_queryset().with_details()

        # Filter by magazine if specified
        magazine_id = self.request.GET.get("magazine")
        if magazine_id:
            queryset = queryset.filter(article__magazine_id=magazine_id)

        return queryset

    def hook_prepare_results(self, results: list[dict[str, Any]]) -> list[dict[str, Any]]:
        """Add formatted_name to each result."""
        for author in results:
            author["formatted_name"] = f"{author['name']} ({author['article_count']} articles)"
        return results
```
:::

## Design and Implementation Notes

- **Key Features**:
  - Dynamic exclusion using `exclude_by`.

- **Design Decisions**:
  - Chose `TomSelectModelMultipleChoiceField` for contributing authors to allow multi-selection.
  - The `exclude_by` parameter ensures clean and efficient backend filtering without additional custom JavaScript.

- **Potential Extensions**:
  - Add metadata to the dropdown options, such as the number of articles authored.
  - Extend the exclusion logic to handle multiple fields (e.g., exclude all team leads from a team member selection).

See the Article List and Create example for a more comprehensive demonstration, which includes this functionality.