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RoutePrefix attribute in Web API

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we will discuss the use of RoutePrefix attribute with an example. 

RoutePrefix attribute : As you can see from the example below, all the routes in the StudentsController start with the same prefix - api/students

public class StudentsController : ApiController
{
    [Route("api/students")]
    public IEnumerable<Student> Get()

    [Route("api/students/{id}")]
    public Student Get(int id)


    [Route("api/students/{id}/courses")]
    public IEnumerable<string> GetStudentCourses(int id)
}



The common prefix "api/students" can be specified for the entire controller using the [RoutePrefix] attribute as shown below. This eliminates the need to repeat the common prefix "api/students" on every controller action method.

[RoutePrefix("api/students")]
public class StudentsController : ApiController
{
    [Route("api/students")]
    public IEnumerable<Student> Get()

    [Route("api/students/{id}")]
    public Student Get(int id) 

    [Route("api/students/{id}/courses")]
    public IEnumerable<string> GetStudentCourses(int id)
}

However, sometimes you may want to override the route prefix. Let us understand this with an example.

Right click on the models folder, and add a new class file. Name it "Teacher.cs". Copy and paste the following code.

namespace WebAPI.Models
{
    public class Teacher
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

Add the following GetTeachers() method to the "StudentsController".

public IEnumerable<Teacher> GetTeachers()
{
    List<Teacher> teachers = new List<Teacher>()
    {
        new Teacher() { Id = 1, Name = "Rob" },
                new Teacher() { Id = 2, Name = "Mike" },
        new Teacher() { Id = 3, Name = "Mary" }
    };

    return teachers;
}

So at this point, "StudentsController" class is as shown below

[RoutePrefix("api/students")]
public class StudentsController : ApiController
{
    static List<Student> students = new List<Student>()
    {
        new Student() { Id = 1, Name = "Tom" },
        new Student() { Id = 2, Name = "Sam" },
        new Student() { Id = 3, Name = "John" }
    };

    [Route("")]
    public IEnumerable<Student> Get()
    {
        return students;
    }

    [Route("{id}")]
    public Student Get(int id)
    {
        return students.FirstOrDefault(s => s.Id == id);
    }

    [Route("{id}/courses")]
    public IEnumerable<string> GetStudentCourses(int id)
    {
        if (id == 1)
            return new List<string>() { "C#", "ASP.NET", "SQL Server" };
        else if (id == 2)
            return new List<string>() { "ASP.NET Web API", "C#", "SQL Server" };
        else
            return new List<string>() { "Bootstrap", "jQuery", "AngularJs" };
    }

    public IEnumerable<Teacher> GetTeachers()
    {
        List<Teacher> teachers = new List<Teacher>()
    {
        new Teacher() { Id = 1, Name = "Rob" },
        new Teacher() { Id = 2, Name = "Mike" },
        new Teacher() { Id = 3, Name = "Mary" }
    };

        return teachers;
    }
}

We want GetTeachers() method to be mapped to URI "/api/teachers".  

[Route("api/teachers")]
public IEnumerable<Teacher> GetTeachers()
{
    List<Teacher> teachers = new List<Teacher>()
    {
        new Teacher() { Id = 1, Name = "Rob" },
        new Teacher() { Id = 2, Name = "Mike" },
        new Teacher() { Id = 3, Name = "Mary" }
    };

    return teachers;
}

If we use the [Route] attribute on GetTeachers() method as shown above and when we navigate to /api/teachers, we get the following error.
No HTTP resource was found that matches the request URI 'http://localhost:65116/api/teachers'.

But if we navigate to /api/students/api/teachers then we get the list of teachers. This is because of the [RoutePrefix("api/students")] attribute on StudentsController. So there is definitely a need to override the RoutePrefix used on the StudentsController. To override the RoutePrefix use ~ as shown below

[Route("~/api/teachers")]
public IEnumerable<Teacher> GetTeachers()
{
    List<Teacher> teachers = new List<Teacher>()
    {
        new Teacher() { Id = 1, Name = "Rob" },
        new Teacher() { Id = 2, Name = "Mike" },
        new Teacher() { Id = 3, Name = "Mary" }
    };

    return teachers;
}

With this change GetTeachers() action method is mapped to URI "/api/teachers" as expected.

What is the use of RoutePrefix attribute
RoutePrefix attribute is used to specify the common route prefix at the controller level to eliminate the need to repeat that common route prefix on every controller action method

How to override the route prefix 
Use ~ character to override the route prefix

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