ASP.NET 迁移正在创建重复的桥接实体

Question

我正在使用 MVC 5 和 EF 6 设计一个 ASP.NET 的 Web 应用程序。我们的团队使用代码优先迁移来设计我们的数据库。在我们的项目中，我们有两个模型 - Location 和 Recreation。 Recreation 本质上是一个可枚举的标签，可以应用于任何 Location（多对多关系），所以我设计了一个 3rd bridge 实体模型来处理关系（所以我可以在代码中引用它）。以下是缩写的模型定义：

地点：

/*
 * Represents a location on a map.
 */
public class Location
{
    public int LocationID { get; set; }
    public String Label { get; set; }
    public double Latitude { get; set; }
    public double Longitude { get; set; }

    public virtual ICollection<Recreation> Recreations { get; set; }
}

娱乐：

/*
 * Represents a recreation activity type, such as Hiking or Camping, that 
 * can be applied to any location as a tag (each Location may have 0 or more
 * Recreation tags).
 */
public class Recreation
{
    public int RecreationID { get; set; }
    public string Label { get; set; }

    public virtual ICollection<Location> Locations { get; set; }
}

桥实体：

/*
 * Bridge entity to handle associations of Location and Recreation
 */
public class LocationRecreation
{
    [Key]
    [ForeignKey("Location")]
    [Column(Order = 1)] 
    [Display(Name = "Location")]
    public int LocationID { get; set; }

    [Key]
    [ForeignKey("Recreation")]
    [Column(Order = 2)]
    [Display(Name = "Recreation")]
    public int RecreationID { get; set; }

    public virtual Location Location { get; set; }
    public virtual Recreation Recreation { get; set; }
}

当我添加迁移和 运行 update-database 时，这适用于 controllers/views 的默认脚手架。但是，在查看“服务器资源管理器”选项卡时，我看到以下 tables:

• Locations
• Recreations
• LocationRecreations
• RecreationLocations（额外的table？）

视图在 LocationRecreations 上处理 CRUD，但虚拟属性指向 RecreationLocations，因此它们不起作用，因为 table 仍然是空的。

What is causing the migrations to create a duplicate table? Can I modify my models in some way to allow for only one table to be created, and so that the virtual properties function as intended?

编辑：

我在 Visual Studio 托管的新项目 here on Github 中重现了错误。为清楚起见，我选择了个人用户帐户，因此在 IdentityModels.cs 文件中为我的数据库上下文使用单个 ApplicationDbContext：

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext()
        : base("DefaultConnection", throwIfV1Schema: false)
    {
    }

    public DbSet<Location> Locations { get; set; }
    public DbSet<Recreation> Recreations { get; set; }

    public static ApplicationDbContext Create()
    {
        return new ApplicationDbContext();
    }


    // Associate a Location with a Recreation.
    public void AddOrUpdateRecreationLocation(string locationLabel, string recreationLabel)
    {
        var location = this.Locations.SingleOrDefault(l => l.Label == locationLabel);
        var recreation = location.Recreations.SingleOrDefault(r => r.Label == recreationLabel);

        //i if it does not exist, register the item.
        if (recreation == null) location.Recreations.Add(this.Recreations.Single(r => r.Label == recreationLabel));
    }
}

Answer 1

我解决了我的问题。 Location 和 Relation 都需要一个 virtual ICollection<LocationRelation>（我的桥实体的集合）。问题是我告诉 entity framework 间接指向相关项目，因此它推断为我创建了第三个桥 table。

LocationRecreation 和 DbContext 代码没问题。以下是修改后的 Location 和 Recreation 模型：

/*
 * Represents a location on a map.
 */
public class Location
{
    public int LocationID { get; set; }
    public String Label { get; set; }
    public double Latitude { get; set; }
    public double Longitude { get; set; }

    public virtual ICollection< LocationRecreation > LocRecs { get; set; }
}

/*
 * Represents a recreation activity type, such as Hiking or Camping, that 
 * can be applied to any location as a tag (each Location may have 0 or more
 * Recreation tags).
 */
public class Recreation
{
    public int RecreationID { get; set; }
    public string Label { get; set; }

    public virtual ICollection< LocationRecreation > LocationRecs { get; set; }
}