ASP.NET Web API query string parameters

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In this video we will discuss using query string parameters in ASP.NET Web API.

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Let us understand query string parameters in ASP.NET Web API with an example.

We want to modify the following Get() method in EmployeesController so that we can retrieve employees by gender
publicclassEmployeesController : ApiController
{
publicIEnumerable<Employee> Get()
{
using (EmployeeDBEntities entities = newEmployeeDBEntities())
{
return entities.Employees.ToList();
}
}
}

 Depending on the value we specify for query string parameter gender, the Get() method should return the data.
Query String Data
http://localhost/api/employees?gender=All All Employees
http://localhost/api/employees?gender=Male Only Male Employees
http://localhost/api/employees?gender=Female Only Female Employees

If the value for gender is not Male, Female or All, then the service should return status code 400 Bad Request. For example, if we specify ABC as the value for gender, then the service should return status code 400 Bad Request with the following message.
Value for gender must be Male, Female or All. ABC is invalid.

Below is the modified Get() method
  1. Gender is being passed as a parameter to the Get() method
  2. Default value is "All". The default value makes the parameter optional
  3. The gender parameter of the Get() method is mapped to the gender parameter sent in the query string
publicHttpResponseMessage Get(string gender = "All")
{
using (EmployeeDBEntities entities = newEmployeeDBEntities())
{
switch (gender.ToLower())
{
case"all":
return Request.CreateResponse(HttpStatusCode.OK,
entities.Employees.ToList());
case"male":
return Request.CreateResponse(HttpStatusCode.OK,
entities.Employees.Where(e => e.Gender.ToLower() == "male").ToList());
case"female":
return Request.CreateResponse(HttpStatusCode.OK,
entities.Employees.Where(e => e.Gender.ToLower() == "female").ToList());
default:
return Request.CreateErrorResponse(HttpStatusCode.BadRequest,
"Value for gender must be Male, Female or All. " + gender + " is invalid.");
}
}
}

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5 comments:

  1. Can anyone please help me with this ?:

    when I am creating the method with return type IHttpActionResult everything is ok, but when I am creating it as above with return type HttpResponseMessage I get the following error :

    Method not found: 'System.Net.Http.HttpRequestMessage System.Web.Http.ApiController.get_Request()'.

    what can I do to make this work ?

    Thank you in advance for your help.

    Reply Delete
    Replies

    1. In Visual Studio, Go to Tools -> NuGet Package Manager -> Manage NuGet Packages for Solution... -> Browse -> Search for "Microsoft.AspNet.WebApi.Client"
      Install it.

      Delete

  2. how to restrict Parameter Manipulation in update user detail page.

    Reply Delete

  3. This comment has been removed by the author.

    Reply Delete

  4. As we know how to use query in get calls, Can we use query string in post calls as well as ?

    Reply Delete

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