使用自動映射器將Entity Framework集合映射為逗號分隔的字符串

Question

我有一個家長班：

public class Parent
{
    ...
    public List<Location> Locations { get; set; }
}

位置類別：

public class Location
{
    public int LocationId { get; set; }
    public string Name { get; set; }
}

映射的目標類：

public class Destination
{
    ...
    public string DelimitedLocations { get; set; }
}

我需要使用自動映射器將LocationId列表從Locations映射到以逗號分隔的字符串。

這是我嘗試過的幾件事：

CreateMap<Parent, Destination>().ForMember(d => d.DelimitedLocations , o => o.MapFrom(s => string.Join(",", s.Locations.ToList().Select(t => t.LocationID.ToString()))))

結果：LINQ to Entities無法識別方法'System.String Join（System.String，System.Collections.Generic.IEnumerable`1 [System.String]）'方法，並且該方法無法轉換為商店表達式。

下次嘗試：

CreateMap<Parent, Destination>()..ForMember(d => d.TestPlotLocationsSelected, o => o.MapFrom(s => s.TestPlotLocations.ToList().Select(t => string.Join(",", t.TestPlotLocationID.ToString()))))

結果：類型'System.Collections.Generic.IEnumerable`1 [System.String]'上不存在方法'ToString'。

不知道下一步該怎么做。

Answer 1

選擇語句應類似於

o.Locations.Select(x => x.LocationId).ToList()

演示版

public class Program
{
    public static void Main()
    {
        Initialize();

        var source = new Parent
        {
            Locations = new List<Location>
            {
                new Location {LocationId = 1, Name = "One"},
                new Location {LocationId = 2, Name = "Two"},
                new Location {LocationId = 3, Name = "Three"},
            }
        };

        var destination = Mapper.Map<Parent, Destination>(source);

        Console.ReadLine();
    }

    public static void Initialize()
    {
        MapperConfiguration = new MapperConfiguration(cfg =>
        {
            cfg.CreateMap<Parent, Destination>()
                .ForMember(dest => dest.DelimitedLocations, mo => mo.MapFrom(src =>
                    src.Locations != null
                        ? string.Join(",", src.Locations.Select(x => x.LocationId).ToList())
                        : ""));
        });
        Mapper = MapperConfiguration.CreateMapper();
    }

    public static IMapper Mapper { get; private set; }

    public static MapperConfiguration MapperConfiguration { get; private set; }
}

public class Parent
{
    public List<Location> Locations { get; set; }
}

public class Location
{
    public int LocationId { get; set; }
    public string Name { get; set; }
}

public class Destination
{
    public string DelimitedLocations { get; set; }
}

結果