Why is my FastAPI endpoint being called when a different endpoint with identical path parameters is defined later?

Multiple API Endpoints with Identical Path Parameter

When designing RESTful APIs using FastAPI, it's possible to define multiple endpoints with different paths but a shared path parameter. However, in cases where endpoint execution becomes inconsistent, it's crucial to address potential configuration issues.

Consider the following router file in FastAPI:

<code class="python"># GET API Endpoint 1
@router.get("/project/{project_id}/{employee_id}")
async def method_one(
    project_id: str, organization_id: str, session: AsyncSession = Depends(get_db)
):
    # Controller method execution

# GET API Endpoint 2
@router.get("/project/details/{project_id}")
async def method_two(
    project_id: str, session: AsyncSession = Depends(get_db)
):
    # Controller method execution

# GET API Endpoint 3
@router.get("/project/metadata/{project_id}")
async def method_three(
    project_id: str, session: AsyncSession = Depends(get_db)
):
    # Controller method execution</code>

When invoking API endpoints 2 and 3, unexpectedly, method_one's controller is executed instead of the expected method_two and method_three. This anomaly requires a careful examination of the configuration.

FastAPI evaluates endpoints in the sequence they are defined. Hence, project/{project_id}/{employee_id} will be evaluated first. Subsequently, any request to endpoints 2 and 3 will trigger endpoint 1.

Solution:

To resolve this issue, reorder the endpoint definitions in the router file, ensuring that endpoints 2 and 3 are defined before endpoint 1:

<code class="python"># GET API Endpoint 2
@router.get("/project/details/{project_id}")
    # ...

# GET API Endpoint 3
@router.get("/project/metadata/{project_id}")
    # ...

# GET API Endpoint 1
@router.get("/project/{project_id}/{employee_id}")
    # ...</code>

By reordering the endpoints, the appropriate controller methods will be executed upon API endpoint invocation.

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