属性表达式无效.表达式应表示一个属性 [英] The properties expression is not valid. The expression should represent a property

问题描述

我有这两个实体

public class Song : IPathHavingEntity
    {
        public int Id { get; set; }
        [Required]
        public string Path { get; set; }
        [Required]
        public virtual Album Album { get; set; }
        [Required]
        public int TrackNumber { get; set; }
    }

public class Album : IPathHavingEntity
    {
        public int Id { get; set; }
        [Required]
        public string Path { get; set; }
        public virtual IEnumerable<Song> Songs { get; set; }
        [Required]
        public int AlbumNumber { get; set; }
    }

Path是在IPathHavingEntity界面中定义的.

在我的Seed方法中，我只想将歌曲添加到Songs表中(如果它不存在).因此，在添加专辑路径和歌曲路径组合之前，我先检查该路径是否不存在

In my Seed method I want to add a song to the Songs table only if it doesn't exist. For this reason I check that the album path and song path combination don't exist already before adding it thus

context.Songs.AddOrUpdate(
    s => new { FilePath = s.Path, AlbumPath = s.Album.Path }, 
    new Song { TrackNumber = 1, Path = "01 Intro.mp3", Album = one });

问题是我收到此错误

The properties expression 's => new <>f__AnonymousType0``2(FilePath = s.Path, AlbumPath = s.Album.Path)' is not valid. The expression should represent a property: C#: 't => t.MyProperty' VB.Net: 'Function(t) t.MyProperty'. When specifying multiple properties use an anonymous type: C#: 't => new { t.MyProperty1, t.MyProperty2 }' VB.Net: 'Function(t) New With { t.MyProperty1, t.MyProperty2 }'.

The properties expression 's => new <>f__AnonymousType0``2(FilePath = s.Path, AlbumPath = s.Album.Path)' is not valid. The expression should represent a property: C#: 't => t.MyProperty' VB.Net: 'Function(t) t.MyProperty'. When specifying multiple properties use an anonymous type: C#: 't => new { t.MyProperty1, t.MyProperty2 }' VB.Net: 'Function(t) New With { t.MyProperty1, t.MyProperty2 }'.

出什么问题了?

推荐答案

今天，我在一个类似的问题上苦苦挣扎了几个小时，终于得以解决.我不确定这是否适合您的情况，但值得调查.

I struggled with a similar issue for several hours today and was finally able to resolve it. I'm not sure if this will work for your situation but it's worth investigating.

该问题可能是由Song实体的Album属性被标记为virtual引起的.我不是EF专家，但是在初始化您的匿名类型时，我不认为它喜欢virtual属性.为相册路径添加非虚拟属性(但保留virtual导航属性)，如下所示:

The problem may be caused by the Album property of your Song entity being marked as virtual. I'm not an EF expert but I don't think it likes that virtual property when initializing your anonymous type. Add a non-virtual property for the album path (but keep the virtual navigation property), like this:

public class Song : IPathHavingEntity
{
    public int Id { get; set; }

    [Required]
    public string Path { get; set; }

    [Required]
    public virtual Album Album { get; set; }

    public string AlbumPath { get; set; }

    [Required]
    public int TrackNumber { get; set; }
}

然后使用该非虚拟属性执行AddOrUpdate，如下所示:

And then perform the AddOrUpdate using that non-virtual property, like this:

context.Songs.AddOrUpdate(
    s => new { FilePath = s.Path, AlbumPath = s.AlbumPath }, 
    new Song { TrackNumber = 1, Path = "01 Intro.mp3", Album = one });

然后，EF应该只允许您添加给定的歌曲路径和专辑路径不存在的歌曲.您的Song域对象是否可以具有非虚拟的AlbumPath属性是另一个问题，但这至少应允许您以描述的方式运行种子方法.

EF should then only allow you to add songs where the given song path and album path do not already exist. Whether your Song domain object can have a non-virtual AlbumPath property is another question but this should at least allow you to run your seed method in the way you described.

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