不能隐式转换类型 &#39;System.Collections.Generic.List<DTO.ProductivityDTO> &#39; 到 &#39;DTO.ProductivityDTO&#39;

Question

So I'm trying to retrieve data from a database to display it in a table. (This is a WebApi project). The idea is to go through all the prodactivity from the table whose status is 1. Put them in some list and return it. To do this, I need to convert a TBL object to DAL. but here I am stuck. It is unable to perform a conversion and is therefore unwilling to return an object of a different type. I tried to convert in all sorts of ways but it'S out of sync with the type in the controller.

This is my code: (do'nt look at the other functions. Look at the function getProductivityRequest at the end)

UserController.cs

using BL;
using DTO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Cors;

namespace WebApiSystem.Controllers
{
    [EnableCors(origins: "*", headers: "*", methods: "*")]//SupportsCredentials = true    
    [RoutePrefix("api/User")]

    public class UserController : ApiController
    {
        [HttpGet]
        [Route("login/{email}/{pass}")]

        public IHttpActionResult LogIn(string email, string pass)
        {
            UserDTO user = BL.UserService.LogIn(email, pass);
            if (user != null)
                return Ok(user);
            return NotFound();
        }

        [Route("register")]
        public IHttpActionResult Register(UserDTO user)
        {    
            return NotFound();
        }

        [HttpPost]
        [Route("productivity")]

        public IHttpActionResult InsertProductivity([FromBody] ProductivityDTO p)
        {
            bool b = BL.UserService.InsertProductivity(p);
            if (b)
                return Ok(b);
            return BadRequest();
        }

        [HttpGet]
        [Route("getProductivityRequest")]

        public IHttpActionResult GetProductivityRequest()
        {
            return Json(BL.UserService.GetProductivityRequest());
        }    
    }
}

UserService.cs

using DAL;
using DTO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BL
{
    public class UserService
    {
        public static UserDTO LogIn(string email, string pass)
        {
            using (Model2 db = new Model2())
            {
                UserTbl user = db.UserTbl.FirstOrDefault(u => u.UserEmail == email && u.UserPassLogin == pass);
                if (user == null)
                    return null;
                return CONVERTERS.UserConverter.ConvertUsertoDTO(user);
            }
        }
        public static bool InsertProductivity(ProductivityDTO p)
        {
            using (Model2 db = new Model2())
            {
                //conver dal to dto
                ProductivityTbl prod = BL.CONVERTERS.ProductivityConverter.ProductivityDal(p);
                prod.ProductivityStatus = 1;
                db.ProductivityTbl.Add(prod);
                db.SaveChanges();
                return true;
            }
            return false;
        }

        public static ProductivityDTO GetProductivityRequest()//Here I can not convert
        {
            using (Model2 db = new Model2())
            {
                List<ProductivityDTO> PList = new List<ProductivityDTO>();

                foreach (var item in db.ProductivityTbl.ToList())
                {
                    if(item.ProductivityStatus==1)
                    {
                        ProductivityDTO prod = BL.CONVERTERS.ProductivityConverter.ConvertProductivitytoDTO(item);                    
                        PList.Add(prod);
                    }                   
                }
                return (PList);//He's unable to return the object

            }
        }
    }
}

ProductivityConverter.cs (if it's relevant...)

using DTO;
using DAL;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BL.CONVERTERS
{
    class ProductivityConverter
    {
   public static ProductivityDTO ConvertProductivitytoDTO(ProductivityTbl productivity) {
            return new ProductivityDTO
            {
                ProductivyCode = productivity.ProductivyCode,
                ProductivityNum = productivity.ProductivityNum,
                ProductivityStatus = productivity.ProductivityStatus,
                UserCode = productivity.UserCode,
                Cmment = productivity.Cmment,
                Date = productivity.Date

            };

        }

        public static ProductivityTbl ProductivityDal(ProductivityDTO productivity)
        {
            return new ProductivityTbl
            {
                ProductivyCode = productivity.ProductivyCode,
                ProductivityNum = productivity.ProductivityNum,
                ProductivityStatus = productivity.ProductivityStatus,
                UserCode = productivity.UserCode,
                Cmment = productivity.Cmment,
                Date = productivity.Date

            };
  
        }
    }
}

If anyone knows of another way to transfer the data I would love ideas.

Thanks!

Answer 1

Your method returns a ProductivityDTO :

public static ProductivityDTO GetProductivityRequest()

...but you are trying to return PList which is a List<ProductivityDTO> .

Your method signature should be:

public static List<ProductivityDTO> GetProductivityRequest()

Although your comment suggests you can't change the method signature. In which case you need to return just one DTO. How you determine which one is up to you. But if it were just one with a ProductivityStatus of 1 then you could do:

        public static ProductivityDTO GetProductivityRequest()//Here I can not convert
        {
            using (Model2 db = new Model2())
            {
                return BL.CONVERTERS.ProductivityConverter.ConvertProductivitytoDTO(db.ProductivityTbl.FirstOrDefault(p => p.ProductivityStatus == 1)));

            }
        }

Answer 2

Your function is defined to return a single ProductivityDTO .
But your function is building a List<ProductivityDTO> and returning that.

Change your function return type to a collection type, such as:

public static List<ProductivityDTO> GetProductivityRequest()

or

public static IEnumerable<ProductivityDTO> GetProductivityRequest()