linq - 我可以在 LINQ to Entities 的 SELECT 中执行子查询以填充模型中的列表吗？

Question

.Select中是否可以有子查询？ LINQ to Entities 的一部分查询以填写 List<string>在我的 View 模型中？我找到了 Use Linq To Entities subquery within Select clause to fetch a field value但是当我尝试这样做时，我收到错误消息:

NotImplementedException: Microsoft.Data.Entity.Query.ResultOperators.Internal.QueryAnnotationResultOperator

这可能与 Entity Framework 7 和 ASP.Net 5 MVC 6 有关吗？

var model = _DbContext.ReleaseVersions
                        .OrderByDescending(rv => rv.DateReleased)
                        .Select(rv => new ReleaseNotesVM()
                        {
                            ID = rv.ID,
                            CurrentVersion = string.Concat(rv.Major, '.', rv.Minor, '.', rv.Patch),
                            ReleaseNotes = _DbContext.ReleaseNotes
                                                    .Where(rn => rn.ReleaseVersionID == rv.ID)
                                                    .Include(rn => rn.ReleaseVersion)
                                                    .Select(rn => rn.Note)
                                                    .ToList()
                        }).FirstOrDefault();

正在填充的 ViewModel:

public class ReleaseNotesVM
{
    public byte ID { get; set; }
    public string CurrentVersion { get; set; }
    public DateTime CurrentVersionReleaseDate { get; set; }
    public IEnumerable<SelectListItem> VersionList { get; set; }
    public byte SelectedVersionID { get; set; }
    public ICollection<string> ReleaseNotes { get; set; }
}

数据模型:

public class ReleaseVersion
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public byte ID { get; set; }

    public DateTime DateReleased { get; set; }
    public byte Major { get; set; }
    public byte Minor { get; set; }
    public byte Patch { get; set; }

    public virtual ICollection<ReleaseNote> ReleaseNotes { get; set; }
}
public class ReleaseNote
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ID { get; set; }

    public string Note { get; set; }
    public byte ReleaseVersionID { get; set; }

    [ForeignKey("ReleaseVersionID")]
    public ReleaseVersion ReleaseVersion { get; set; }
}

Answer 1

如果我假设正确，您必须在 ReleaseVersions 之间建立一对多关系。和 ReleaseNotes ，这意味着 ReleaseVersion 中应该有导航属性类指的是 ReleaseNotes 的集合，使您能够像这样重写代码:

var model = _DbContext.ReleaseVersions
                    .Include(rv => rv.ReleaseNotes)
                    .OrderByDescending(rv => rv.DateReleased)
                    .Select(rv => new ReleaseNotesVM
                    {
                        ID = rv.ID,
                        CurrentVersion = string.Concat(rv.Major, '.', rv.Minor, '.', rv.Patch),
                        ReleaseNotes = rv.ReleaseNotes.Select(rn => rn.Note).ToList()
                    }).FirstOrDefault();

更新

使用 List<string> ReleaseNotes而不是 ICollection<string>在 ReleaseNotesVM .