entity-framework-4 - 使用 C# 和 Entity Framework CTP 4 的领域建模问题

Question

我正在尝试建模一个包含照片集的相册。每个相册都有一组照片和一张拇指照片。这就是我所拥有的，但 EF 似乎不喜欢它:

public class Album : IEntity {
        private DateTime _dateCreated;

        public Album() {
            _dateCreated = SystemTime.Now();
            Photos = new List<Photo>();
        }
        public long Id { get; set; }
        public string Name { get; set; }
        public string Location { get; set; }
        public DateTime DateCreated
        {
            get { return _dateCreated; }
            set { _dateCreated = value; }
        }
        public virtual Site Site { get; set; }
        public virtual Photo Thumbnail { get; set; }
        public virtual ICollection<Photo> Photos { get; set; }
    }

public class Photo : IEntity {
            public Photo() {
                _dateCreated = SystemTime.Now();
            }
            private DateTime _dateCreated;
            public long Id { get; set; }
            public string Caption { get; set; }
            public string FileName { get; set; }
            public DateTime DateCreated
            {
                get { return _dateCreated; }
                set { _dateCreated = value; }
            }
            public virtual Album Album { get; set; }

        }

 public class AlbumMap : EntityConfiguration<Album>
    {
        public AlbumMap()
        {
            HasKey(x => x.Id);
            Property(x => x.Id).IsIdentity();
            Property(x => x.Location).IsVariableLength().HasMaxLength(80);
            Property(x => x.Name).IsVariableLength().HasMaxLength(80).IsRequired();
            Property(x => x.DateCreated);
            MapSingleType(a => new
            {
                a.Id,
                SiteId = a.Site.Id,
                ThumbnailId = a.Thumbnail.Id,
                a.Location,
                a.Name,
                a.DateCreated
            }).ToTable("Albums");
        }
    }

public class PhotoMap : EntityConfiguration<Photo>
    {
        public PhotoMap()
        {
            HasKey(x => x.Id);
            Property(x => x.Id).IsIdentity();
            Property(x => x.FileName).IsVariableLength().HasMaxLength(255).IsRequired();
            Property(x => x.Caption).IsVariableLength().HasMaxLength(255);
            Property(x => x.DateCreated);
            MapSingleType(a => new
            {
                a.Id,
                SiteAlbumId = a.Album.Id,
                a.FileName,
                a.Caption,
                a.DateCreated
            }).ToTable("AlbumPhotos");
        }
    }

我错过了什么还是这看起来正确？我希望 EF 在我的数据库中生成 1 对多，但它一直在创建相册和照片 (Album_Photos) 之间的引用表，但这不应该是多对多。任何帮助都会很棒。

Answer 1

按照惯例，EF 代码首先不会在典型的一对多场景中创建链接表，您得到它的原因是因为您的 Album 和 Photo 对象之间的关联已被 EF 视为一种多对多关联:

每个相册都有一个照片集合，并且每个照片都有一个相册集合，这张照片是缩略图(尽管在 Photo 类中没有明确指定相关的导航属性，只有相册有缩略图属性)。

解决方案:

从 EF CTP4 开始，解决此问题的唯一方法是利用 Fluent API，但在此之前，我稍微修改了您的模型并向您的模型添加了两个显式 FK，以便为您提供处理对象的最大灵活性。他们是 AlbumId在 Photo和 ThumbnailId在 Album :

public class Photo {        
    public long Id { get; set; }
    public string Caption { get; set; }
    public string FileName { get; set; }
    public DateTime DateCreated { get; set; }

    public long AlbumId { get; set; }
    public virtual Album Album { get; set; }
}

public class Album {
    public long Id { get; set; }
    public string Name { get; set; }
    public string Location { get; set; }
    public DateTime DateCreated { get; set; }

    public long ThumbnailId { get; set; }
    public virtual Photo Thumbnail { get; set; }

    public virtual ICollection<Photo> Photos { get; set; }
}

public class PhotoMap : EntityConfiguration<Photo> {
    public PhotoMap() 
    {
        this.HasRequired(p => p.Album)
            .WithMany(a => a.Photos)
            .HasConstraint((p, a) => p.AlbumId == a.Id);

        Property(x => x.FileName).IsVariableLength().HasMaxLength(255)
                                                    .IsRequired();
        Property(x => x.Caption).IsVariableLength().HasMaxLength(255);
        MapSingleType(p => new {
            p.Id,
            SiteAlbumId = p.AlbumId,
            p.FileName,
            p.Caption,
            p.DateCreated
        })
        .ToTable("Photo");
    }
}

public class AlbumMap : EntityConfiguration<Album> {
    public AlbumMap()
    {
        this.HasRequired(a => a.Thumbnail)
            .WithMany()
            .WillCascadeOnDelete(false)
            .HasConstraint((a, p) => p.Id == a.ThumbnailId);

        Property(x => x.Location).IsVariableLength().HasMaxLength(80);
        Property(x => x.Name).IsVariableLength().HasMaxLength(80).IsRequired();
        MapSingleType(a => new {
            a.Id,
            a.ThumbnailId,
            a.Location,
            a.Name,
            a.DateCreated
        })
        .ToTable("Album");
    }
}

这导致以下所需的架构: