如何在EF Core模型类中修改外键关联至UniColumn而非主键

现有以下EF Core模型类：

public enum Roster
{
    None,
    One,
    Two,
    Three,
    Four
}

[Index(nameof(UniColumn), IsUnique = true)]
internal class RowRosterEnum
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [EnumDataType(typeof(Roster))]
    public Roster RosterEnum { get; set; }

    public Roster UniColumn { get; set; }
}

internal class RowRoster
{
    [Key]
    [ForeignKey(nameof(RowRosterEnum))]
    public Roster RId { get; set; }

    public string? Name { get; set; }

    public RowRosterEnum RowRosterEnum { get; set; }
}

创建迁移时生成的代码如下：

migrationBuilder.CreateTable(
                name: "TableRosterEnum",
                columns: table => new
                {
                    RosterEnum = table.Column<int>(type: "int", nullable: false),
                    UniColumn = table.Column<int>(type: "int", nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_TableRosterEnum", x => x.RosterEnum);
                });

            migrationBuilder.CreateTable(
                name: "TableRoster",
                columns: table => new
                {
                    RId = table.Column<int>(type: "int", nullable: false),
                    Name = table.Column<string>(type: "nvarchar(max)", nullable: true)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_TableRoster", x => x.RId);
                    table.ForeignKey(
                        name: "FK_TableRoster_TableRosterEnum_RId",
                        column: x => x.RId,
                        principalTable: "TableRosterEnum",
                        principalColumn: "RosterEnum",
                        onDelete: ReferentialAction.Cascade);
                });

            migrationBuilder.CreateIndex(
                name: "IX_TableRosterEnum_UniColumn",
                table: "TableRosterEnum",
                column: "UniColumn",
                unique: true);

需求：修改模型类，使RowRoster的外键关联到RowRosterEnum的UniColumn（即迁移代码中principalColumn为"UniColumn"），同时保留RosterEnum作为RowRosterEnum的主键。

EF Core默认会将外键关联到主表的主键列，要实现需求需手动指定主表的关联列，以下两种方式均可实现：

方式一：使用数据注解修改模型 #

通过显式声明外键属性和关联列来调整关系：

public enum Roster
{
    None,
    One,
    Two,
    Three,
    Four
}

[Index(nameof(UniColumn), IsUnique = true)]
internal class RowRosterEnum
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [EnumDataType(typeof(Roster))]
    public Roster RosterEnum { get; set; }

    public Roster UniColumn { get; set; }

    // 添加导航属性，辅助EF Core识别关联关系
    public ICollection<RowRoster> RowRosters { get; set; } = new List<RowRoster>();
}

internal class RowRoster
{
    [Key]
    public Roster RId { get; set; }

    public string? Name { get; set; }

    // 指定外键关联到RowRosterEnum的UniColumn列
    [ForeignKey(nameof(UniColumn))]
    public RowRosterEnum RowRosterEnum { get; set; }

    // 声明对应主表UniColumn的外键属性
    public Roster UniColumn { get; set; }
}

方式二：使用Fluent API配置（推荐，关系配置更清晰） #

保持模型类简洁，在DbContext的OnModelCreating方法中配置关联规则：

修改后的模型类 #

public enum Roster
{
    None,
    One,
    Two,
    Three,
    Four
}

[Index(nameof(UniColumn), IsUnique = true)]
internal class RowRosterEnum
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [EnumDataType(typeof(Roster))]
    public Roster RosterEnum { get; set; }

    public Roster UniColumn { get; set; }

    public ICollection<RowRoster> RowRosters { get; set; } = new List<RowRoster>();
}

internal class RowRoster
{
    [Key]
    public Roster RId { get; set; }

    public string? Name { get; set; }

    public RowRosterEnum RowRosterEnum { get; set; }

    public Roster UniColumn { get; set; }
}

在DbContext中配置关系 #

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<RowRoster>()
        .HasOne(r => r.RowRosterEnum)
        .WithMany(e => e.RowRosters)
        .HasForeignKey(r => r.UniColumn) // 指定RowRoster的外键列
        .HasPrincipalKey(e => e.UniColumn); // 指定RowRosterEnum的关联列
}

修改后迁移代码效果 #

重新生成迁移后，外键部分会变为：

table.ForeignKey(
    name: "FK_TableRoster_TableRosterEnum_UniColumn",
    column: x => x.UniColumn,
    principalTable: "TableRosterEnum",
    principalColumn: "UniColumn",
    onDelete: ReferentialAction.Cascade);

此时RowRoster表会新增UniColumn列作为外键关联到RowRosterEnum的UniColumn，RId依然是RowRoster的主键，RosterEnum也保留为RowRosterEnum的主键。

内容的提问来源于stack exchange，提问作者user9163823