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Route Parameters in Asp.net Core

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Route Parameters in Asp.net Core
Types of Route Parameters
Required Parameters:
Syntax: Enclosed in curly braces {}.
Behavior: Must be provided in the URL for the route to match. If not present, the request won’t match this endpoint.
Example: /products/{id} (The id parameter is required).
Optional Parameters:
Syntax: Enclosed in curly braces {} and followed by a question mark ?.
Behavior: Can be omitted from the URL. If not present, the parameter’s value will be null.
Example: /products/details/{id?} (The id parameter is optional).
Parameters with Default Values:
Syntax: Enclosed in curly braces {}, followed by an equals sign =, and then the default value.
Behavior: If not provided in the URL, the parameter will take the specified default value.
Example: /employee/profile/{EmployeeName=harsha} (The EmployeeName parameter defaults to “harsha”).
Code:
// … (UseRouting and other middleware) …
 
app.UseEndpoints(endpoints =>
{
    // Required Parameters
    endpoints.Map(“files/{filename}.{extension}”, async context =>
    {
        string? fileName = Convert.ToString(context.Request.RouteValues[“filename”]);
        string? extension = Convert.ToString(context.Request.RouteValues[“extension”]);
 
        await context.Response.WriteAsync($”In files – {fileName} – {extension}”);
    });
 
    // Default Parameter
    endpoints.Map(“employee/profile/{EmployeeName=harsha}”, async context =>
    {
        string? employeeName = Convert.ToString(context.Request.RouteValues[“employeename”]);
        await context.Response.WriteAsync($”In Employee profile – {employeeName}”);
    });
 
    // Optional Parameter
    endpoints.Map(“products/details/{id?}”, async context => {
        if (context.Request.RouteValues.ContainsKey(“id”))
        {
            int id = Convert.ToInt32(context.Request.RouteValues[“id”]);
            await context.Response.WriteAsync($”Products details – {id}”);
        }
        else
        {
            await context.Response.WriteAsync($”Products details – id is not supplied”);
        }
    });
});
 
// … (Fallback middleware) …
 
Required Parameters Example:
The route files/{filename}.{extension} expects both filename and extension to be present in the URL (e.g., /files/sample.txt).
The endpoint handler extracts these values from context.Request.RouteValues and uses them in the response.
Default Parameter Example:
The route employee/profile/{EmployeeName=harsha} has a default value for EmployeeName.
If you visit /employee/profile, the response will be “In Employee profile – harsha”.
If you visit /employee/profile/john, the response will be “In Employee profile – john”.
Optional Parameter Example:
The route products/details/{id?} allows the id parameter to be omitted.
If you visit /products/details/123, it will show the product details for ID 123.
If you visit /products/details, it will indicate that the ID was not provided.

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