命令更新迁移、Entity Framework 3.15、Net Core 3.1 中的错误答案

【问题标题】：Error in command update-migration, Entity Framework 3.15, Net Core 3.1命令更新迁移、Entity Framework 3.15、Net Core 3.1 中的错误
【发布时间】：2021-08-24 07:12:53
【问题描述】：

我已经定义了我的模板并在 DbContext 中引用，但是当我运行 update-database 命令时，它会生成错误：找不到“InstitutionContact”对象，因为它不存在或没有权限。

验证它创建的迁移，可以清楚地看到产生了错误，因为它创建了一个不存在的表的更新迁移，而不是表创建迁移。如果我要更新的表不存在，如何避免创建更新迁移？如何创建我需要的表？

迁移

using Microsoft.EntityFrameworkCore.Migrations;

命名空间 DegreeProjectsSystem.DataAccess.Migrations { 公共部分类 AddTableInstitutionContacts ：迁移 { protected override void Up(MigrationBuilder migrationBuilder) { migrationBuilder.DropForeignKey( 名称：“FK_InstitutionContact_InstitutionContactCharges_InstitutionContactChargeId”，表：“机构联系方式”）；

        migrationBuilder.DropForeignKey(
            name: "FK_InstitutionContact_Institutions_InstitutionId",
            table: "InstitutionContact");

        migrationBuilder.DropForeignKey(
            name: "FK_InstitutionContact_People_PersonId",
            table: "InstitutionContact");

        migrationBuilder.RenameTable(
            name: "InstitutionContact",
            newName: "InstitutionContacts");

        migrationBuilder.AlterColumn<int>(
            name: "PersonId",
            table: "InstitutionContacts",
            nullable: false,
            oldClrType: typeof(int),
            oldNullable: true);

        migrationBuilder.AlterColumn<int>(
            name: "InstitutionId",
            table: "InstitutionContacts",
            nullable: false,
            oldClrType: typeof(int),
            oldNullable: true);

        migrationBuilder.AlterColumn<int>(
            name: "InstitutionContactChargeId",
            table: "InstitutionContacts",
            nullable: false,
            oldClrType: typeof(int),
            oldNullable: true);

        migrationBuilder.AddColumn<int>(
            name: "Id",
            table: "InstitutionContacts",
            nullable: false,
            defaultValue: 0)
            .Annotation("SqlServer:Identity", "1, 1");

        migrationBuilder.AddColumn<bool>(
            name: "Active",
            table: "InstitutionContacts",
            nullable: false,
            defaultValue: false);

        migrationBuilder.AddPrimaryKey(
            name: "PK_InstitutionContacts",
            table: "InstitutionContacts",
            column: "Id");

        migrationBuilder.CreateIndex(
            name: "IX_InstitutionContacts_InstitutionContactChargeId",
            table: "InstitutionContacts",
            column: "InstitutionContactChargeId");

        migrationBuilder.CreateIndex(
            name: "IX_InstitutionContacts_PersonId",
            table: "InstitutionContacts",
            column: "PersonId");

        migrationBuilder.CreateIndex(
            name: "IX_InstitutionContacts_InstitutionId_PersonId_InstitutionContactChargeId",
            table: "InstitutionContacts",
            columns: new[] { "InstitutionId", "PersonId", "InstitutionContactChargeId" },
            unique: true);

        migrationBuilder.AddForeignKey(
            name: "FK_InstitutionContacts_InstitutionContactCharges_InstitutionContactChargeId",
            table: "InstitutionContacts",
            column: "InstitutionContactChargeId",
            principalTable: "InstitutionContactCharges",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);

        migrationBuilder.AddForeignKey(
            name: "FK_InstitutionContacts_Institutions_InstitutionId",
            table: "InstitutionContacts",
            column: "InstitutionId",
            principalTable: "Institutions",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);

        migrationBuilder.AddForeignKey(
            name: "FK_InstitutionContacts_People_PersonId",
            table: "InstitutionContacts",
            column: "PersonId",
            principalTable: "People",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DropForeignKey(
            name: "FK_InstitutionContacts_InstitutionContactCharges_InstitutionContactChargeId",
            table: "InstitutionContacts");

        migrationBuilder.DropForeignKey(
            name: "FK_InstitutionContacts_Institutions_InstitutionId",
            table: "InstitutionContacts");

        migrationBuilder.DropForeignKey(
            name: "FK_InstitutionContacts_People_PersonId",
            table: "InstitutionContacts");

        migrationBuilder.DropPrimaryKey(
            name: "PK_InstitutionContacts",
            table: "InstitutionContacts");

        migrationBuilder.DropIndex(
            name: "IX_InstitutionContacts_InstitutionContactChargeId",
            table: "InstitutionContacts");

        migrationBuilder.DropIndex(
            name: "IX_InstitutionContacts_PersonId",
            table: "InstitutionContacts");

        migrationBuilder.DropIndex(
            name: "IX_InstitutionContacts_InstitutionId_PersonId_InstitutionContactChargeId",
            table: "InstitutionContacts");

        migrationBuilder.DropColumn(
            name: "Id",
            table: "InstitutionContacts");

        migrationBuilder.DropColumn(
            name: "Active",
            table: "InstitutionContacts");

        migrationBuilder.RenameTable(
            name: "InstitutionContacts",
            newName: "InstitutionContact");

        migrationBuilder.AlterColumn<int>(
            name: "PersonId",
            table: "InstitutionContact",
            nullable: true,
            oldClrType: typeof(int));

        migrationBuilder.AlterColumn<int>(
            name: "InstitutionId",
            table: "InstitutionContact",
            nullable: true,
            oldClrType: typeof(int));

        migrationBuilder.AlterColumn<int>(
            name: "InstitutionContactChargeId",
            table: "InstitutionContact",
            nullable: true,
            oldClrType: typeof(int));

        migrationBuilder.AddForeignKey(
            name: "FK_InstitutionContact_InstitutionContactCharges_InstitutionContactChargeId",
            table: "InstitutionContact",
            column: "InstitutionContactChargeId",
            principalTable: "InstitutionContactCharges",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);

        migrationBuilder.AddForeignKey(
            name: "FK_InstitutionContact_Institutions_InstitutionId",
            table: "InstitutionContact",
            column: "InstitutionId",
            principalTable: "Institutions",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);

        migrationBuilder.AddForeignKey(
            name: "FK_InstitutionContact_People_PersonId",
            table: "InstitutionContact",
            column: "PersonId",
            principalTable: "People",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
    }
}

}

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace DegreeProjectsSystem.Models
{
    public class InstitutionContact
    {
        [Key]
        public int Id { get; set; }
        
        [Required(AllowEmptyStrings = false, ErrorMessage = "Debe seleccionar una Institución")]
        public int InstitutionId { get; set; }
        
        [Display(Name = "Institución")]
        //Foreign key
        [ForeignKey("InstitutionId")]
        public Institution Institution { get; set; }
        
        [Required(AllowEmptyStrings = false, ErrorMessage = "Debe seleccionar un Contacto")]
        public int PersonId { get; set; }
        
        [Display(Name = "Contacto")]
        //Foreign key
        [ForeignKey("PersonId")]
        public Person Person { get; set; }
        
        [Required(AllowEmptyStrings = false, ErrorMessage = "Debe seleccionar el cargo del Contacto")]
        public int InstitutionContactChargeId { get; set; }
        
        [Display(Name = "Cargo")]
        //Foreign key
        [ForeignKey("InstitutionContactChargeId")]
        public InstitutionContactCharge InstitutionContactCharge { get; set; }
        
        [Display(Name = "Estado")]
        public bool Active { get; set; }
        }
        }
    }
}

【问题讨论】：

尝试删除迁移文件中 Up 方法和 down 方法中的代码。然后运行命令更新数据库
解决方案无效，它不会产生错误但也不会创建表。
您是否曾经删除过任何迁移？ Bevause 好像你做到了。您的模型快照可能已经包含该表的定义。

标签： c# entity-framework entity-framework-migrations

【解决方案1】：

解决办法是：

我从项目中删除了所有迁移。
我删除了
数据库。
我生成了第一个迁移。
在运行更新迁移之前，我修改了一些主键因创建级联而产生错误的关系默认删除，改变 onDelete: ReferentialAction.Cascade 到 onDelete：ReferentialAction.NoAction。
创建新的迁移以重建数据库。

【讨论】：