Body was inferred but the method does not allow inferred body parameters:error

I faced the below error when I worked with Aspnet minimal Api.

crit: Microsoft.AspNetCore.Hosting.Diagnostics[6]
Application startup exception
System.InvalidOperationException: Body was inferred but the method does not allow inferred body parameters.
Below is the list of parameters that we found:
Parameter | Source
---------------------------------------------------------------------------------
user | Body (Inferred)
Did you mean to register the "Body (Inferred)" parameter(s) as a Service or apply the [FromServices] or [FromBody] attribute?

this error occurred because I made get method and in the parameters, I try to receive a UserInputModel which is not allowed in the get request and to fix I changed MapGet to MapPost.

wrong one:
app.MapGet("/sinun", sinup);
async Task<string> sinup(UserInputModel user)
{......

correct one:
//correct version
app.MapPost("/sinun", sinup);
async Task<string> sinup(UserInputModel user)
...
{


More information about the error

The error message occurs during the startup of an ASP.NET Core application, and it's a System.InvalidOperationException. This indicates that something is wrong with how a method in your application is handling its parameters, specifically related to inferring body parameters.

Breakdown of the Error Message:

1. "Application startup exception":

   • This indicates that the error occurred during the startup phase of your ASP.NET Core application, preventing it from running correctly.

2. "Body was inferred but the method does not allow inferred body parameters":

   • The framework inferred that one of the method parameters (user) should be bound from the body of the HTTP request, but the method you're using does not allow parameters to be inferred in this way.
   • Typically, when a parameter is expected to be provided in the body of a request (e.g., in JSON format), it needs to be explicitly marked with the [FromBody] attribute.

3. "Below is the list of parameters that we found":

   • The message lists the parameters the framework found and how they were inferred:

    Parameter           | Source
    ---------------------------------------------------------------------------------
    user                | Body (Inferred)
   

• In this case, it inferred that user should come from the request body.

1. "Did you mean to register the 'Body (Inferred)' parameter(s) as a Service or apply the [FromServices] or [FromBody] attribute?":
   • This part of the message suggests possible fixes:
     • Use [FromBody]: If the user parameter is supposed to come from the body of the HTTP request, explicitly mark it with [FromBody].
     • Use [FromServices]: If the user parameter is meant to be injected from a service (like a dependency), you should use [FromServices].

Example Scenario:

Suppose you have a method like this in your controller:

public IActionResult Register(User user)
{
    // Registration logic
}

If this method is meant to handle a POST request with a User object in the body, you need to specify where the user parameter should come from:

public IActionResult Register([FromBody] User user)
{
    // Registration logic
}

Why the Error Happens:

• ASP.NET Core's minimal APIs and some modern frameworks allow parameters to be inferred from various parts of the request (like the body, query string, or route), but this only works in certain contexts.
• In your case, it appears that the method is not configured to allow inference, or the framework couldn't determine the source of the parameter correctly.

How to Fix:

1. Explicitly Specify Parameter Sources:

   • If the user parameter should come from the request body, add the [FromBody] attribute to it:

    public IActionResult Register([FromBody] User user)
    {
        // Your logic here
    }
   

2. Ensure Method Signature Matches Expected Usage:

   • Make sure the method is designed to accept parameters as intended (e.g., from the body, services, query string, etc.).

3. Check the Routing and Middleware Setup:

   • Verify that your application is configured correctly in terms of routing and middleware. Misconfigurations can sometimes cause these kinds of issues.

By addressing these issues, the application should be able to start without encountering this exception.