EF Core 迁移从新的复合索引中删除第一个外键索引

Question

这是我的模型：

public class Period
{
    [Key]
    public int Id { get; set; }
}

public class Company
{
    [Key]
    public int Id { get; set; }
}

public class Invoice
{
    [Key]
    public int Id { get; set; }

    public int PeriodId { get; set; }
    public Period Period { get; set; }

    public int CompanyId { get; set; }
    public Company Company { get; set; }
}

没什么特别的。一张包含期间和公司的简单发票。

这是它们的配置方式：

modelBuilder.Entity<Invoice>()
    .HasOne(p => p.Period)
    .WithMany()
    .OnDelete(DeleteBehavior.Restrict)
;

modelBuilder.Entity<Invoice>()
    .HasOne(p => p.Company)
    .WithMany()
    .OnDelete(DeleteBehavior.Restrict)
;

这是一个由此生成的迁移文件：

migrationBuilder.CreateTable(
    name: "Companies",
    columns: table => new
    {
        Id = table.Column<int>(nullable: false)
            .Annotation("SqlServer:Identity", "1, 1")
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_Companies", x => x.Id);
    });

migrationBuilder.CreateTable(
    name: "Periods",
    columns: table => new
    {
        Id = table.Column<int>(nullable: false)
            .Annotation("SqlServer:Identity", "1, 1")
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_Periods", x => x.Id);
    });

migrationBuilder.CreateTable(
    name: "Invoices",
    columns: table => new
    {
        Id = table.Column<int>(nullable: false)
            .Annotation("SqlServer:Identity", "1, 1"),
        PeriodId = table.Column<int>(nullable: false),
        CompanyId = table.Column<int>(nullable: false)
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_Invoices", x => x.Id);
        table.ForeignKey(
            name: "FK_Invoices_Companies_CompanyId",
            column: x => x.CompanyId,
            principalTable: "Companies",
            principalColumn: "Id",
            onDelete: ReferentialAction.Restrict);
        table.ForeignKey(
            name: "FK_Invoices_Periods_PeriodId",
            column: x => x.PeriodId,
            principalTable: "Periods",
            principalColumn: "Id",
            onDelete: ReferentialAction.Restrict);
    });

migrationBuilder.CreateIndex(
    name: "IX_Invoices_CompanyId",
    table: "Invoices",
    column: "CompanyId");

migrationBuilder.CreateIndex(
    name: "IX_Invoices_PeriodId",
    table: "Invoices",
    column: "PeriodId");

一切似乎都是合法的。现在我需要创建一个唯一索引来控制公司发票在一段时间内的唯一性：

modelBuilder.Entity<Invoice>()
    .HasIndex(p => new
    {
        p.PeriodId,
        p.CompanyId,
    })
    .IsUnique()
;

这就是迁移现在的样子：

migrationBuilder.DropIndex(
    name: "IX_Invoices_PeriodId",
    table: "Invoices");

migrationBuilder.CreateIndex(
    name: "IX_Invoices_PeriodId_CompanyId",
    table: "Invoices",
    columns: new[] { "PeriodId", "CompanyId" },
    unique: true);

注意“DropIndex”。它从我的复合索引中获取第一列。如果我更改顺序，它仍然会丢弃第一个：

modelBuilder.Entity<Invoice>()
    .HasIndex(p => new
    {
        p.CompanyId,
        p.PeriodId,
    })
    .IsUnique()
;

migrationBuilder.DropIndex(
    name: "IX_Invoices_CompanyId",
    table: "Invoices");

migrationBuilder.CreateIndex(
    name: "IX_Invoices_CompanyId_PeriodId",
    table: "Invoices",
    columns: new[] { "CompanyId", "PeriodId" },
    unique: true);

我不确定我是否理解这背后的逻辑。复合索引中是否有任何特殊之处使单独的索引无用？或者可能是某种错误？

我发现这个问题的唯一提及是关于 SO 的一个有点过时的帖子： EF Migrations drops index when adding compsite index

附：使用 SQL Server 作为数据库提供程序在 3.1.8 上进行了测试。

Answer 1

应该更彻底地研究这个问题。 创建复合索引时，它的第一列可以在查询中单独使用。 https://github.com/dotnet/efcore/issues/22513