Advanced FastAPI Path Parameters: Dynamic Routing and Parameter Validation
FastAPI supports dynamic routing and parameter validation with flexibility and robustness. Basic usage includes paths like `/users/{user_id}`, where parameters can be automatically type-identified (e.g., `int`), and conversion failures return a 422 error. For advanced dynamic routing, it supports automatic type conversion, optional parameters (`Optional` with default values), and regex restrictions (`Path.pattern`), such as for order codes requiring an 8-character combination of uppercase letters/numbers (`^[A-Z0-9]{8}$`). Advanced parameter validation is achieved by setting ranges (`ge`/`le`) via `Path` or using enumeration types, e.g., product IDs must be `ge=1, le=99`, and order types restricted to the enum values `pending/completed/cancelled`. By combining dynamic routing with validation, a general interface is constructed, reducing manual validation code. The Swagger documentation (`/docs`) allows intuitive testing of these rules.
Read MoreFlask URL Construction: The url_for Function and Dynamic Routes
This article introduces the key methods for URL construction and handling in Flask, addressing the maintenance issues of hard-coded URLs. The core lies in the `url_for` function and dynamic routing. The `url_for` function dynamically generates URLs through view function names, avoiding hard-coding. Its basic usage is `url_for('view_function_name', parameter=value)`, such as generating the home page URL with `url_for('index')`. It supports parameter passing, e.g., `url_for('user_profile', user_id=100)` generates `/user/100`. By using `_external=True`, absolute URLs can be created, which are suitable for scenarios like emails or redirects. Dynamic routing allows route rules to include variable parameters, with the syntax `<converter:parameter_name>`. Converters include `int` (integer), `string` (string), and `path` (string with slashes), among others. The parameter name must match the view function parameter, and the type must be consistent; otherwise, a 404 error is returned. When combined, `url_for` is used in templates or views to generate links for dynamic routes. When route rules change, there is no need to modify the code, thus enhancing the maintainability of the project.
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