从一端定义关系有效，但从另一端定义它会导致错误

Question

为什么在OnModelCreating中调用base后的第一行会出错？抛出的注释行导致此错误：

表达式 'x => value(Blog.Services.Db).ContentItems' 不是有效的属性表达式。该表达式应表示属性访问：'t => t.MyProperty'。参数名称：属性AccessExpression

    protected override void OnModelCreating(ModelBuilder mb)
    {
        base.OnModelCreating(mb);
        mb.Entity<ContentGroup>().HasMany(x => ContentItems).WithOne(x => x.ContentGroup).HasForeignKey(x => x.ContentGroupID);  // same effect as following line but throws an error
        //mb.Entity<ContentItem>().HasOne(x => x.ContentGroup).WithMany(x => x.ContentItems).HasForeignKey(x => x.ContentGroupID); // same effect as previous line but works

    }

内容组：

public class ContentGroup
{
    public int ID { get; set; }
    public int SiteID { get; set; }
    public string Description { get; set; }
    public int Sequence { get; set; }
    public bool Active { get; set; }
    public virtual Site Site { get; set; }
    public virtual ICollection<ContentItem> ContentItems { get; set; }
}

内容项：

public class ContentItem
{
    public int ID { get; set; }
    public string ContentType { get; set; }
    public int ContentGroupID { get; set; }
    public DateTime? PublishDate { get; set; }
    public DateTime? LastModifyDate { get; set; }
    public string ChangeFrequency { get; set; }
    public decimal? Priority { get; set; }
    public bool Active { get; set; }
    public string Slug { get; set; }
    public string Title { get; set; }
    public string MenuText { get; set; }
    public string URI { get; set; }
    public string Abstract { get; set; }
    public string Icon { get; set; }
    public string Tags { get; set; }
    public bool AllowComments { get; set; }
    public virtual ICollection<Comment> Comments { get; set; }
    public virtual ContentGroup ContentGroup { get; set; }
    public virtual ICollection<MenuContentItem> MenuContentItems { get; set; }
}

Answer 1

在第一个语句中，HasForeignKey() 方法反映到 ContentGroup 实体而不是 ContentItem 实体。 ContentGroup 实体没有 ContentGroupId 属性这就是它不起作用的原因。

更新：

The expression 'x => value(Blog.Services.Db).ContentItems' is not a valid property expression. The expression should represent a property access: 't => t.MyProperty'. Parameter name: propertyAccessExpression

根据出现的异常消息，因为在第一个语句中你有 .HasMany(x => ContentItems) 但它应该是 .HasMany(x => x.ContentItems).

从一端定义关系有效，但从另一端定义它会导致错误

Defining a relationship from one end works, but defining it from the other end causes an error

c#

entity-framework-core