Filtering in ASP.NET Core 2.0 Web API

• Download source code from Github

Problem

How to implement filtering in ASP.NET Core Web API.

Solution

To an empty project, update Startup class to add services and middleware for MVC:

public void ConfigureServices(
            IServiceCollection services)
        {
            services.AddSingleton<IMovieService, MovieService>();

            services.AddMvc();
        }

        public void Configure(
            IApplicationBuilder app,
            IHostingEnvironment env)
        {
            app.UseDeveloperExceptionPage();
            app.UseMvcWithDefaultRoute();
        }

Add model to hold filtering data:

public class FilteringParams
    {
        public string FilterBy { get; set; } = "";
    }

Add a service and domain model:

public interface IMovieService
    {
        List<Movie> GetMovies(FilteringParams filteringParams);
    }
    public class MovieService : IMovieService
    {
        public List<Movie> GetMovies(FilteringParams filteringParams)
        {
            var query = this.movies.AsQueryable();

            var filterBy = filteringParams.FilterBy.Trim().ToLowerInvariant();
            if (!string.IsNullOrEmpty(filterBy))
            {
                query = query
                       .Where(m => m.LeadActor.ToLowerInvariant().Contains(filterBy)
                       || m.Title.ToLowerInvariant().Contains(filterBy)
                       || m.Summary.ToLowerInvariant().Contains(filterBy));
            }

            return query.ToList();
        }
    }

    public class Movie
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public int ReleaseYear { get; set; }
        public string Summary { get; set; }
        public string LeadActor { get; set; }
    }

Add output models (to send data via API):

public class MovieOutputModel
    {
        public int Count { get; set; }
        public List<MovieInfo> Items { get; set; }
    }

    public class MovieInfo
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public int ReleaseYear { get; set; }
        public string Summary { get; set; }
        public string LeadActor { get; set; }
        public DateTime LastReadAt { get; set; }
    }

Add a controller for the API with service injected via constructor:

[Route("movies")]
    public class MoviesController : Controller
    {
        private readonly IMovieService service;

        public MoviesController(IMovieService service)
        {
            this.service = service;
        }

        [HttpGet(Name = "GetMovies")]
        public IActionResult Get(FilteringParams filteringParams)
        {
            var model = service.GetMovies(filteringParams);
            
            var outputModel = new MovieOutputModel
            {
                Count = model.Count,
                Items = model.Select(m => ToMovieInfo(m)).ToList(),
            };
            return Ok(outputModel);
        }
    }

Output:

Discussion

Let’s walk through the sample code step-by-step:

1. Filtering information is usually received via query parameters. The POCO FilteringParams simply hold this information and passes to service (or repository).
2. Service will then filter the data and returns a list.
3. We build our output model MovieOutputModel and return status code 200(OK). The output model contains:
   1. Total number of items returned by the server.
   2. List of movies. As discussed in the previous post (CRUD), we map the domain model to an output model (MovieInfo in this case).