与 EF Core 的一对一关系

Question

我想要实现的是有一个模型CommentsThread ，它可以附加到任何其他需要评论的模型，无论是Chapter 、 BlogPost 、 UserProfile ，还是你有什么。 基本上，我需要的结构是

CommentsThread
  int ID

Chapter
  int ID
  int Thread FK(CommentsThread.ID)

BlogPost
  int ID
  int Thread FK(CommentsThread.ID)

UserProfile
  int ID
  int Thread FK(CommentsThread.ID)

但是我不知道如何在 EF 核心中正确配置它，而不必向CommentsThread模型添加对Chapter 、 BlogPost和UserProfile可为空引用。

我的CommentsThread代码如下：

public class CommentsThread
{
    [Key]
    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    public ICollection<Comment> Comments { get; set; }
}

而Chapter ，省略了任何不相关的属性，是

public class Chapter
{
    [Key]
    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public CommentsThread CommentsThread { get; set; }
}

使用以下 Fluent 配置（再次跳过不相关的位）：

builder.Entity<CommentsThread>()
    .HasMany(ct => ct.Comments)
    .WithOne()
    .OnDelete(DeleteBehavior.Cascade);

builder.Entity<Chapter>()
    .HasOne(c => c.CommentsThread)
    .WithOne()
    .OnDelete(DeleteBehavior.Cascade);

在dotnet ef migrations add X它将此输出抛出到控制台。

---

更新：

所以，我尝试明确添加public int CommentsThreadId { get; set; } public int CommentsThreadId { get; set; } public int CommentsThreadId { get; set; }在Chapter和改变配置来

builder.Entity<Chapter>()
    .HasOne(c => c.CommentsThread)
    .WithOne()
    .HasForeignKey<Chapter>(c => c.CommentsThreadId)
    .OnDelete(DeleteBehavior.Cascade);

这确实使迁移通过了，但在database update时失败了

The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.Chapters' and the index name 'IX_Chapters_CommentsThreadId'. The duplicate key value is (0).
The statement has been terminated.

Answer 1

AFAIK，有两种方法可以配置 1-1 关系：

1. https://www.entityframeworktutorial.net/efcore/one-to-one-conventions-entity-framework-core.aspx
2. https://weblogs.asp.net/manavi/inheritance-mapping-strategies-with-entity-framework-code-first-ctp5-part-2-table-per-type-tpt

第一个帖子需要每个模型的参考。 但你提到：

无需添加可为空引用

那么，只有第二个概念（每个类型的表）可以达到您的目标，但是该帖子对于 EF Core 来说太旧了。

以下是新的数据模型：

public class CommentsThread
{
    [Key]
    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

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

    public ICollection<ThreadComment> Comments { get; set; }
}

[Table(nameof(Chapter))]
public class Chapter
{
    [Key]
    [Required]
    [ForeignKey(nameof(CommentsThread))]
    public int Id { get; set; }

    public int Number { get; set; }

    public CommentsThread CommentsThread { get; set; }
}
[Table(nameof(BlogPost))]
public class BlogPost
{
    [Key]
    [Required]
    [ForeignKey(nameof(CommentsThread))]
    public int Id { get; set; }

    public string Author { get; set; }

    public CommentsThread CommentsThread { get; set; }
}

[Table(nameof(UserProfile))]
public class UserProfile
{
    [Key]
    [Required]
    [ForeignKey(nameof(CommentsThread))]
    public int Id { get; set; }
    public string Bio { get; set; }

    public CommentsThread CommentsThread { get; set; }
}

public class ThreadComment
{
    [Key]
    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

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

    public CommentsThread CommentsThread { get; set; }
}

这是示例上下文：

public class ApplicationDbContext : IdentityDbContext
{
    public virtual DbSet<CommentsThread> CommentsThreads { get; set; }
    public virtual DbSet<Chapter> Chapters { get; set; }
    public virtual DbSet<BlogPost> BlogPosts { get; set; }
    public virtual DbSet<UserProfile> UserProfiles { get; set; }
    public virtual DbSet<ThreadComment> ThreadComments { get; set; }

    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }


    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Chapter>().ToTable(nameof(Chapter));
        modelBuilder.Entity<BlogPost>().ToTable(nameof(BlogPost));
        modelBuilder.Entity<UserProfile>().ToTable(nameof(UserProfile));
    }
}

这是生成的迁移代码：

public partial class AddCommentsThread : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.CreateTable(
            name: "CommentsThreads",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false)
                    .Annotation("SqlServer:Identity", "1, 1"),
                Title = table.Column<string>(nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_CommentsThreads", x => x.Id);
            });

        migrationBuilder.CreateTable(
            name: "BlogPost",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false),
                Author = table.Column<string>(nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_BlogPost", x => x.Id);
                table.ForeignKey(
                    name: "FK_BlogPost_CommentsThreads_Id",
                    column: x => x.Id,
                    principalTable: "CommentsThreads",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateTable(
            name: "Chapter",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false),
                Number = table.Column<int>(nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Chapter", x => x.Id);
                table.ForeignKey(
                    name: "FK_Chapter_CommentsThreads_Id",
                    column: x => x.Id,
                    principalTable: "CommentsThreads",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateTable(
            name: "ThreadComments",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false)
                    .Annotation("SqlServer:Identity", "1, 1"),
                Content = table.Column<string>(nullable: false),
                CommentsThreadId = table.Column<int>(nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_ThreadComments", x => x.Id);
                table.ForeignKey(
                    name: "FK_ThreadComments_CommentsThreads_CommentsThreadId",
                    column: x => x.CommentsThreadId,
                    principalTable: "CommentsThreads",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Restrict);
            });

        migrationBuilder.CreateTable(
            name: "UserProfile",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false),
                Bio = table.Column<string>(nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_UserProfile", x => x.Id);
                table.ForeignKey(
                    name: "FK_UserProfile_CommentsThreads_Id",
                    column: x => x.Id,
                    principalTable: "CommentsThreads",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateIndex(
            name: "IX_ThreadComments_CommentsThreadId",
            table: "ThreadComments",
            column: "CommentsThreadId");
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DropTable(
            name: "BlogPost");

        migrationBuilder.DropTable(
            name: "Chapter");

        migrationBuilder.DropTable(
            name: "ThreadComments");

        migrationBuilder.DropTable(
            name: "UserProfile");

        migrationBuilder.DropTable(
            name: "CommentsThreads");
    }
}

以下是结果截图：

Answer 2

你的数据库迁移错误；

The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.Chapters' and the index name 'IX_Chapters_CommentsThreadId'. The duplicate key value is (0).
The statement has been terminated.

是由于向已包含数据的表添加了非空列。 如果您想为每种记录类型强制存在一个CommentsThread ，您还需要编写一个迁移脚本来为现有数据插入这些记录。

或者只是将外键列类型更改为int? 所以它将允许空值。