Django Validation in a Text Flowchart
Published: 2024-06-02 19:34:59

In Django, form validation is an important process that ensures the data submitted by users is accurate and safe before being processed or stored. This process is structured into multiple stages, each handling different aspects of validation and cleaning.

Understanding these stages is essential for developers who wish to customize or extend the validation behavior in their applications.

The validation process begins with the `form.is_valid()` method, which initiates the overall validation sequence. This method triggers several functions that work in tandem to clean and validate each field in the form:

**`Field.to_python()`**: Converts the input value to the correct datatype. If the conversion fails, it raises a `ValidationError`.

**`Field.validate()`**: Handles field-specific validation that cannot be managed by validators. This method does not alter the value but raises a `ValidationError` if the data is invalid.

**`Field.run_validators()`**: Executes all the validators associated with the field, aggregating any errors into a single `ValidationError`.

**`Field.clean()`**: Coordinates the execution of `to_python()`, `validate()`, and `run_validators()`, ensuring they run in the correct order and propagate any errors that arise.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/8culdzgyheupg91nxmf0.png)

After these individual field validation methods, Django allows for further customization with `form.clean_<fieldname>()` methods, which handle validation specific to individual form fields beyond the type-specific checks.

At the end, the `form.clean()` method provides a place for cross-field validation, allowing developers to enforce rules that involve multiple form fields.

Throughout this process, any function can raise a `ValidationError`, which halts the validation sequence and returns the error. This structured approach ensures that data is thoroughly checked and cleaned before any further processing, maintaining the integrity and security of the application.

```
Form Data Input
       |
       v
+-----------------+
| form.is_valid() |
| Initiates form  |
| validation      |
+-----------------+
       |
       v
+-------------------+
| Field.to_python() |
| Converts value to |
| correct datatype  |
+-------------------+
       |
       v
+------------------+
| Field.validate() |
| Handles field-   |
| specific         |
| validation       |
+------------------+
       |
       v
+-----------------------+
| Field.run_validators()|
| Runs field's          |
| validators            |
+-----------------------+
       |
       v
+---------------------+
| Field.clean()       |
| Runs to_python(),   |
| validate(), and     |
| run_validators()    |
+---------------------+
       |
       v
+--------------------------+
| form.clean_<fieldname>() |
| Cleans specific field    |
| attribute                |
+--------------------------+
       |
       v
+------------------+
| Form.clean()     |
| Validates       |
| multiple form   |
| fields          |
+------------------+
       |
       v
+----------------+
| Validated Data |
+----------------+
```

**References**:

- Form and field validation | Django documentation. (n.d.). Django Project. https://docs.djangoproject.com/en/5.0/ref/forms/validation/