为什么我不允许执行此迁移？

Question

我有一个 postgres 数据库，我首先使用 ef 来控制我的迁移代码。

我目前有这张桌子/班级。

public class Notification
{
    [Key]
    public Guid Id { get; set; } = Guid.NewGuid();

    public string ActionType { get; set; } = string.Empty;
    public string ActionElement { get; set; } = string.Empty;
    public string ActionElementType { get; set; } = string.Empty;

    public string Message { get; set; } = string.Empty;

    public User ForUser { get; set; } = new User();
    public User ByUser { get; set; } = new User();

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public bool Seen { get; set; } = false;
    public bool Clicked { get; set; } = false;
}

to this

public class Notification
{
    [Key]
    public Guid Id { get; set; } = Guid.NewGuid();

    public string ActionType { get; set; } = string.Empty;
    public string ActionElement { get; set; } = string.Empty;
    public string ActionElementType { get; set; } = string.Empty;

    //public string Message { get; set; } = string.Empty;
    
    public Message MessageContent { get; set; };

    public User ForUser { get; set; } = new User();
    public User ByUser { get; set; } = new User();

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public bool Seen { get; set; } = false;
    public bool Clicked { get; set; } = false;
}

public record Message
{
    [Key]
    public Guid MessageId { get; set; } = Guid.NewGuid();

    public string MessageContent { get; init; }
    public ImmutableDictionary<string, string> MessageContentProperties { get; init; }
}

创建了此迁移文件：

/// 公共部分类changeMessageStringToMessageRecord：迁移 { /// protected override void Up(MigrationBuilder migrationBuilder) { 迁移Builder.DropColumn( 名称：“消息”， 表：“通知”）；

        migrationBuilder.AlterDatabase()
            .Annotation("Npgsql:PostgresExtension:hstore", ",,")
            .Annotation("Npgsql:PostgresExtension:uuid-ossp", ",,")
            .OldAnnotation("Npgsql:PostgresExtension:uuid-ossp", ",,");

        migrationBuilder.AddColumn<Guid>(
            name: "MessageContentMessageId",
            table: "Notifications",
            type: "uuid",
            nullable: false,
            defaultValue: new Guid("00000000-0000-0000-0000-000000000000"));

        migrationBuilder.CreateTable(
            name: "Message",
            columns: table => new
            {
                MessageId = table.Column<Guid>(type: "uuid", nullable: false, defaultValueSql: "uuid_generate_v4()"),
                MessageContent = table.Column<string>(type: "text", nullable: false),
                MessageContentProperties = table.Column<ImmutableDictionary<string, string>>(type: "hstore", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Message", x => x.MessageId);
            });

        migrationBuilder.CreateIndex(
            name: "IX_Notifications_MessageContentMessageId",
            table: "Notifications",
            column: "MessageContentMessageId");

        migrationBuilder.AddForeignKey(
            name: "FK_Notifications_Message_MessageContentMessageId",
            table: "Notifications",
            column: "MessageContentMessageId",
            principalTable: "Message",
            principalColumn: "MessageId",
            onDelete: ReferentialAction.Cascade);
    }

    /// <inheritdoc />
    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DropForeignKey(
            name: "FK_Notifications_Message_MessageContentMessageId",
            table: "Notifications");

        migrationBuilder.DropTable(
            name: "Message");

        migrationBuilder.DropIndex(
            name: "IX_Notifications_MessageContentMessageId",
            table: "Notifications");

        migrationBuilder.DropColumn(
            name: "MessageContentMessageId",
            table: "Notifications");

        migrationBuilder.AlterDatabase()
            .Annotation("Npgsql:PostgresExtension:uuid-ossp", ",,")
            .OldAnnotation("Npgsql:PostgresExtension:hstore", ",,")
            .OldAnnotation("Npgsql:PostgresExtension:uuid-ossp", ",,");

        migrationBuilder.AddColumn<string>(
            name: "Message",
            table: "Notifications",
            type: "text",
            nullable: false,
            defaultValue: "");
    }
}

当我应用迁移时，我收到错误消息

ALTER TABLE "Notifications" ADD CONSTRAINT "FK_Notifications_Message_MessageContentMessageId" FOREIGN KEY ("MessageContentMessageId") REFERENCES "Message" ("MessageId") ON DELETE CASCADE;
Npgsql.PostgresException (0x80004005): 23503: insert or update on table "Notifications" violates foreign key constraint "FK_Notifications_Message_MessageContentMessageId"

我不确定我是否理解这里的问题？为什么这里有外键问题？

Answer 1

您的通知表可能有一个

MessageContentMessageId

，但它未映射到

MessageId

列中具有相同

Message

的行。

如果您想要外键，则需要清理数据。

例如，在迁移中，您可以包含一条更新语句来删除所有无法找到的内容，方法是添加一条 SQL 语句将无法找到的消息的

MessageContentMessageId

设置为

NULL

您可以将其包装在

migrationBuilder.Sql

函数中

UPDATE Notifications
SET MessageContentMessageId = NULL
FROM Notifications AS n
LEFT JOIN Messages AS m on m.MessageId = n.MessageContentMessageId
WHERE m.MessageId IS NULL