How would you implement a dependency requiring multi-source parameters?
Tests if you know FastAPI resolves dependency params like endpoint params. Great answers annotate each parameter with its source inside the dependency so FastAPI injects them independently. Red flag: manually parsing Request or merging values in the endpoint.
Tests deep familiarity with FastAPI's dependency injection engine. A strong answer explains that dependency callables are treated like path operations: FastAPI inspects the signature and resolves each parameter using annotations like Path, Header, Query, or Cookie. You declare the dependency with annotated parameters and inject it via Depends. The framework handles sub-dependencies recursively. Red flags include manually parsing Request or extracting values in the endpoint rather than letting FastAPI resolve them automatically.
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