From Scratch: Flask Form Handling and WTForms Validation
This article introduces the core knowledge of handling forms in Flask using the Flask-WTF extension. Flask-WTF is built on WTForms and provides form creation, validation, and CSRF protection. For environment preparation, install `flask` and `flask-wtf`. The core is defining form classes that inherit from `FlaskForm`, using field types like `StringField` and `PasswordField`, and pairing them with validators such as `DataRequired` and `Email` to define rules (e.g., non-empty, format, length). In view functions, instantiate the form and use `form.validate_on_submit()` to handle POST requests and validate data integrity. Templates should use `form.hidden_tag()` to generate CSRF tokens and loop through `form.xxx.errors` to display error messages. After successful validation, retrieve data from `form.xxx.data` and combine it with database storage (e.g., SQLAlchemy). Key process: Define form class → View processing → Template rendering → Data validation and processing. Use WTForms validators to implement checks for non-empty, format, etc., combined with CSRF protection for security, enabling rapid construction of reliable form systems.
Read MoreFlask Form Handling: Complete Process from User Input to Data Display
This article introduces the complete process of implementing form handling using Flask and Flask-WTF, suitable for web development scenarios requiring user information collection. First, install the Flask and Flask-WTF extensions, then create form classes by inheriting the `FlaskForm` class, defining fields (e.g., username, password) and validation rules (required, length, email format, etc.). In Flask applications, view functions must handle GET (rendering the form) and POST (validating submitted data) requests. Use `form.validate_on_submit()` to check the request type and validate data. If validation fails, error messages are stored in `form.<field>.errors`, and templates display errors through loops. Templates must include `form.hidden_tag()` to enable CSRF protection and avoid form submission failures. Key details include: setting `SECRET_KEY` to ensure CSRF security, using redirects to prevent duplicate submissions, and encrypting stored data (e.g., passwords with bcrypt). The complete workflow is: user fills out form → frontend validation → backend validation → data processing → result display. Advanced features can extend to custom validators, multi-form handling, or file uploads. This article helps quickly master core skills of Flask form implementation from definition to data processing.
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