c# - 在不删除数据的情况下重命名 Entity Framework Core 中的外键

Question

我有两个模型类:

public class Survey
{
    public int SurveyId { get; set; }
    public string Name { get; set; }
}

public class User
{
    public int UserId { get; set; }

    public int SurveyId { get; set; }
    public Survey Survey { get; set; }
}

我想将 Survey 重命名为 StudentSurvey，这样它将具有 StudentSurveyId。我相应地更新了模型中的类名和属性，并添加了一个迁移。

但是，我得到:

The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_User_Surveys_SurveyId". The conflict occurred in database "AppName", table "dbo.Survey", column 'SurveyId'.

我认为它正在尝试删除数据，因为它需要列中的数据(不能为空)，所以我看到了该错误。但我不想删除数据。我怎样才能重命名它？

Answer 1

EF Core 将实体类重命名视为删除旧实体并添加新实体，因此生成迁移以删除原始表并创建新表。

解决方法需要执行以下步骤:

(1) 在重命名实体之前，使用 ToTable 和 HasColumnName 流畅的 API 或数据注释“重命名”表和 PK 列。也对引用实体的 FK 列执行相同的操作。

例如:

[Table("StudentSurveys")]
public class Survey
{
    [Column("StudentSurveyId")]
    public int SurveyId { get; set; }
    public string Name { get; set; }
}

public class User
{
    public int UserId { get; set; }
    [Column("StudentSurveyId")]
    public int SurveyId { get; set; }
    public Survey Survey { get; set; }
}

(2) 添加新迁移。它将正确重命名表、PK 列、FK 列和关联的约束:

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.DropForeignKey(
        name: "FK_Users_Surveys_SurveyId",
        table: "Users");

    migrationBuilder.DropPrimaryKey(
        name: "PK_Surveys",
        table: "Surveys");

    migrationBuilder.RenameTable(
        name: "Surveys",
        newName: "StudentSurveys");

    migrationBuilder.RenameColumn(
        name: "SurveyId",
        table: "Users",
        newName: "StudentSurveyId");

    migrationBuilder.RenameIndex(
        name: "IX_Users_SurveyId",
        table: "Users",
        newName: "IX_Users_StudentSurveyId");

    migrationBuilder.RenameColumn(
        name: "SurveyId",
        table: "StudentSurveys",
        newName: "StudentSurveyId");

    migrationBuilder.AddPrimaryKey(
        name: "PK_StudentSurveys",
        table: "StudentSurveys",
        column: "StudentSurveyId");

    migrationBuilder.AddForeignKey(
        name: "FK_Users_StudentSurveys_StudentSurveyId",
        table: "Users",
        column: "StudentSurveyId",
        principalTable: "StudentSurveys",
        principalColumn: "StudentSurveyId",
        onDelete: ReferentialAction.Cascade);
}

(3) 删除注解/流式配置并进行实际的类/属性重命名:

public class StudentSurvey
{
    public int StudentSurveyId { get; set; }
    public string Name { get; set; }
}

public class User
{
    public int SurveyUserId { get; set; }
    public int StudentSurveyId { get; set; }
    public StudentSurvey StudentSurvey { get; set; }
}

重命名相应的 DbSet(如果有):

public DbSet<StudentSurvey> StudentSurveys { get; set; }

你就完成了。

您可以通过添加新的迁移来验证这一点 - 它将具有空的 Up 和 Down 方法。