Making a generic query / getbyspecification in web api controller?

Question

I have a typical API with some CRUD operations. I typically need to get certain objects, based on different parameters.

One way to do it would be to have methods like:

GetProjectsByCustomerId(int customerId);
GetProjectsBySigneeId(int signeeId);

However, in my service layer (ProjectService in this case) I usually use a method such as the following where ProjectSpecification typically has quite a lot of fields and even lists:

public IEnumerable<Project> GetBySpecification(ProjectSpecification projectSpecification)

That means, in my dream world I would like to have endpoints such as:

/api/projects (empty specification, return full list)
/api/projects?customerid=2 (gets projects for customer with id 2)
/api/projects?signeeid=2,3 (get projects with signee id 2 and 3)

My question is - how is this done

My first attempt was adding this in my ProjectController (calling my ProjectService):

public class ProjectsController : ApiController
{
    public IEnumerable<Project> GetProjects(ProjectSpecification projectSpecification)
    {
        var projects = _projectService.GetBySpecification(projectSpecification);
        return projects;
    }
}

But lets say I open this URL:

/api/Projects?CustomerId=2

This is not parsed into a ProjectSpecification viewmodel. However, if I change my controller signature to:

public IEnumerable<Project> GetProjects(int customerid) { }

It would work, because it's a simple type.

I could of course build some parameter-hell, but I guess there is something super obvious MVC magic I am missing - probably in the routing? :-)

Show ProjectSpecification as part of the example. Also look into the FromUri attribute on the parameter — Nkosi
– Nkosi, Commented Aug 15, 2017 at 14:26
The ProjectSpecification class would work fine, but you may need to build a custom model binder (not hard at all). Alternatively you may want to look at OData which pretty much does this for you anyway. — DavidG
– DavidG, Commented Aug 15, 2017 at 14:27
@DavidG I think you're right that ODATA would probably be what I want, but for the purpose here lets stick with REST. What would be the simplest example of a custom modal binder here? (Thanks btw =) ) — Lars Holdgaard
– Lars Holdgaard, Commented Aug 15, 2017 at 14:29
Take a look here: learn.microsoft.com/en-us/aspnet/core/mvc/advanced/… — DavidG
– DavidG, Commented Aug 15, 2017 at 14:30
For web api look at this learn.microsoft.com/en-us/aspnet/web-api/overview/… . [FromUri] should be simple enough for this scenario. — Nkosi
– Nkosi, Commented Aug 15, 2017 at 14:31

Nkosi · Accepted Answer · 2017-08-15 14:43:45Z

1

Referencing documentation

Parameter Binding in ASP.NET Web API : [FromUri]

To force Web API to read a complex type from the URI, add the [FromUri] attribute to the parameter.

For example assuming

public class ProjectSpecification {
    public int CustomerId { get; set; }
    //...other properties
}

public class ProjectsController : ApiController {
    [HttpGet]
    public IHttpActinoResult GetProjects([FromUri]ProjectSpecification projectSpecification) {
        return Ok(projectSpecification);
    }
}

The client can put the CustomerId value in the query string.

For example:

/api/Projects?CustomerId=2

and Web API will use them to construct a ProjectSpecification with the CustomerId set to 2 .

answered Aug 15, 2017 at 14:43

Nkosi

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