asp.net-core - Entity Framework 核心 : Scaffolding to Avoid Data Loss after to change Model/Entity

Question

我有以下模型:

public class Promotion : BaseModel
{
    [Required]
    public string Description { get; set; }

    [Required]
    public string Market { get; set; }

    [Required]
    public double Price { get; set; }
}

它创建了一个更新到数据库的迁移。并且在数据库中插入了一些促销信息。但是我需要将促销模型更改为:

public class Promotion : BaseModel
{
    [Required]
    public string Description { get; set; }

    [Required]
    public Market Market { get; set; }

    [Required]
    public double Price { get; set; }
}

public class Market : BaseModel
{
    [Required]
    public string Name { get; set; }

    [Required]
    public string Adress { get; set; }
}

当我添加一个新的迁移时，我收到警报:“一个操作是脚手架，可能会导致数据丢失。请检查迁移的准确性。”

这是新迁移的自动生成的 Up 方法:

protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DropColumn(
            name: "Market",
            table: "Promotions");

        migrationBuilder.AddColumn<Guid>(
            name: "MarketId",
            table: "Promotions",
            nullable: false,
            defaultValue: new Guid("00000000-0000-0000-0000-000000000000"));

        migrationBuilder.CreateTable(
            name: "Markets",
            columns: table => new
            {
                Id = table.Column<Guid>(nullable: false),
                Adress = table.Column<string>(nullable: false),
                CreatedAt = table.Column<DateTime>(nullable: false),
                DeletedAt = table.Column<DateTime>(nullable: false),
                Name = table.Column<string>(nullable: false),
                UpdatedAt = table.Column<DateTime>(nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Markets", x => x.Id);
            });

        migrationBuilder.CreateIndex(
            name: "IX_Promotions_MarketId",
            table: "Promotions",
            column: "MarketId");

        migrationBuilder.AddForeignKey(
            name: "FK_Promotions_Markets_MarketId",
            table: "Promotions",
            column: "MarketId",
            principalTable: "Markets",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
    }

如何在不丢失数据的情况下更新数据库？

Answer 1

升级生产数据库的安全方法是将其分解为多个步骤:

添加新的 Market 实体并将其附加到 Promotion 实体 without dropping the existing column

EF 将为您生成迁移 - CREATE TABLE + ADD FOREIGN KEY 语句

使您的代码从 Market table 和 Market column 中更新/插入/选择新值，更喜欢 Market table

你部署这个。现在，您已经获得了包含数据的旧列和新表，并与新数据同步。

编写数据迁移，将旧值从 Market column 复制到 Market table 。运行。现在您已将数据移至新的 Market table 并且新数据位于 Market table

更新您的代码以停止使用旧的 Market column 。部署更改

从您的实体中删除 Market column。 EF 将生成迁移，其中列将被删除。部署这个。您现在已迁移数据和架构