ASP.NET Core 10.0: Validation Support for Minimal APIs

With ASP.NET Core 10.0, we now have built in validation support for Minimal APIs for request data in following.

• Route parameters, Query Strings
• Header
• Request body

If any validation fails, the runtime returns a 400 Bad Request response with details of the validation errors.

Validations are defined using attributes in the System.ComponentModel.DataAnnotations namespace. We can even create our own validators using,

• Creating custom  ValidationAttribute implementations.
• Implementing the IValidatableObject interface

To register validation services and enable validation, we need to call the following method in the Program.cs.

builder.Services.AddValidation();

Now we can do something like below to validate route parameters.

app.MapGet("/employees/{employeeId}", ([Range(1, int.MaxValue)] int employeeId) =>
{
    // Omitted
});

And if we try the endpoint with an incorrect route parameter, we will get an validation error.

GET {{WebApplication1_HostAddress}}/employees/0
Accept: application/json

Route parameter validation

We can use the similar concept with record types as well.

Say I have the following Employee record that has a annotated property.

internal record Employee([Required] string Name);

And now If I try to make a request to the following endpoint,

app.MapPost("/employees", (Employee employee) =>
{
    // Omitted 
});

With a empty value for name,

POST {{WebApplication1_HostAddress}}/employees
Content-Type: application/json
{
    "name": ""
}

I am getting the following 400 Bad Request.

Request Body Validation

You can disable the validation at the endpoint by calling DisableValidation(), something like below:

app.MapPost("/employees", (Employee employee) =>
    {
        // Omitted
    })
    .DisableValidation();

Hope this helps.

Happy Coding.

Regards,

Jaliya