Hands-On Full：Stack Web Development with ASP.NET Core

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Query strings

A query string is data that's sent as part of the URL that is not suitable for use as part of the hierarchical structure of the URL (where / separates between different levels of the hierarchy). Typically, the query string is the part that comes after the question mark in the URL and uses the & sign to separate between the different values. For example, the GiveNTake application allows the user to search for products in a specific location, and to constraint the search only to products that have an image attached to them. This API is exposed through a URL in the following format:

/api/products/searchcategory/category/subcategory?location=XXX&imageonly=true

ASP.NET Core automatically matches any value in the query string to a method parameter with the same name (this value is case-insensitive); therefore, the method in the controller is implemented like this:

[HttpGet("searchcategory/{category}/{subcategory=all}/")]
public string[] SearchByProducts(string category,string subcategory, string location="all", bool imageOnly=false )
{
    return new[]
    {
        $"Category: {category}, Subcategory: {subcategory}, Location: {location}, Only with Images: {imageOnly}"
    };
}

Run the application and navigate to
http://localhost:[port]/api/products/searchcategory/furniture/kitchen?location=center&imageonly=true.

Your browser should show a result similar to this:

By default, simple types are automatically mapped from the request query string to method parameters with the same name. If needed, you can force ASP.NET Core to map a method parameter to a query string value with a different name by using the [FromQuery("name")] attribute. The [FromQuery] attribute also allows you to force the binding to a complex type.

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