EF Core：在同一表中的项目之间创建链接

假设我有一个公司列表：

假设我们想展示这一点CompanyA是的竞争对手CompanyB and CompanyC但不是CompanyD.

我想使用 EF Core 建立这样的链接/映射。我假设我需要创建一个映射表，在数据库中将如下所示：

竞争对手地图：

我正在努力解决的是如何在OnModelCreating(ModelBuilder modelBuilder) method?

我已经能够在两个不同表中的实体之间创建映射，但无法配置DBContext此用例的类（其中映射的实体位于同一个表中）。

如果是我的话我会这样做

公司模式

public class Company
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<CompanyCompetitorRelation> CompanyRelation { get; set; }
    public virtual ICollection<CompanyCompetitorRelation> CompetitorRelation { get; set; }
}

在这个模型中，我说它与 CompanyCompetiorRelation 模型有 2 个关系。

现在为公司竞争对手关系模型

public class CompanyCompetitorRelation
{
    public int CompanyId { get; set; }
    public int CompetitorId { get; set; }
    public virtual Company CompanyRelation { get; set; }
    public virtual Company CompetitorRelation { get; set; }
}

现在，我想说的是 CompanyCompetiorRelation 与公司模型有 2 个关系。

现在 Fluent API 的魔力将发挥作用

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<Company>()
        .HasKey(e => e.Id);

    builder.Entity<CompanyCompetitorRelation>()
        .HasKey(e => new { e.CompanyId, e.CompetitorId });

    builder.Entity<CompanyCompetitorRelation>()
        // CompanyCompetitorRelation property
        .HasOne(e => e.CompanyRelation)
        // Company property
        .WithMany(e => e.CompanyRelation) 
        // Set the property that is FK for this relation
        .HasForeignKey(e => e.CompanyId); 

    builder.Entity<CompanyCompetitorRelation>()
        // CompanyCompetitorRelation property
        .HasOne(e => e.CompetitorRelation) 
        // Company property
        .WithMany(e => e.CompetitorRelation) 
        // Set the property that is FK for this relation
        .HasForeignKey(e => e.CompetitorId); 
}

在第一组FK上builder.Entity<CompanyCompetitorRelation>()我是说它与许多公司都有一个 CompanyRelation，并且外键是 CompanyId

在第二组FK上builder.Entity<CompanyCompetitorRelation>()我是说它作为与许多公司的一种 CompetitorRelation 关系，并且外键是 CompetitorId

这是它生成的

migrationBuilder.CreateTable(
name: "Company",
columns: table => new
{
    Id = table.Column<int>(type: "int", nullable: false)
        .Annotation("SqlServer:Identity", "1, 1"),
    Name = table.Column<string>(type: "nvarchar(max)", nullable: true)
},
constraints: table =>
{
    table.PrimaryKey("PK_Company", x => x.Id);
});

migrationBuilder.CreateTable(
    name: "CompanyCompetitorRelation",
    columns: table => new
    {
        CompanyId = table.Column<int>(type: "int", nullable: false),
        CompetitorId = table.Column<int>(type: "int", nullable: false)
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_CompanyCompetitorRelation", x => new { x.CompanyId, x.CompetitorId });
        table.ForeignKey(
            name: "FK_CompanyCompetitorRelation_Company_CompanyId",
            column: x => x.CompanyId,
            principalTable: "Company",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
        table.ForeignKey(
            name: "FK_CompanyCompetitorRelation_Company_CompetitorId",
            column: x => x.CompetitorId,
            principalTable: "Company",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
    });

migrationBuilder.CreateIndex(
    name: "IX_CompanyCompetitorRelation_CompetitorId",
    table: "CompanyCompetitorRelation",
    column: "CompetitorId");

希望这有助于理解

如果需要，您可以创建任意数量的内容，只需在 Fluent API 上将它们指向正确的方向即可

我认为在模型上也可以这样做，但我喜欢使用 FluentAPI