应用所有 EF Core 迁移后运行代码

Question

EF Core 5 有各种

事件，但它们与 DbContext

 相关。没有与迁移相关的事件 (

Migration

)。

我想在应用所有迁移后运行自定义代码 - 无论是由代码 (

context.Database.Migrate()

) 还是 CLI (

dotnet ef database update

) 触发。

解决方法是添加一个“空”迁移，并将我的代码放入其

Up

 方法中。但每次添加迁移时我都需要这样做。

假设没有我可以使用的事件或挂钩（有吗？），在应用所有迁移后如何运行自定义代码？

Answer 1

这是一个解决方法。

[DbContext(typeof(MyContext))]
[Migration("99999999999999_Last1")]
public class Last1 : Migration {
  protected override void Up(MigrationBuilder migrationBuilder) {
    Task.Run(() => callPostMigrationCodeThatIsIdempotent()).GetAwaiter().GetResult();
    migrationBuilder.DeleteData(HistoryRepository.DefaultTableName, nameof(HistoryRow.MigrationId), "string", "99999999999999_Last2", null);
  }
}

[DbContext(typeof(MyContext))]
[Migration("99999999999999_Last2")]
public class Last2 : Migration {
  protected override void Up(MigrationBuilder migrationBuilder) {
    Task.Run(() => callPostMigrationCodeThatIsIdempotent()).GetAwaiter().GetResult();
    migrationBuilder.DeleteData(HistoryRepository.DefaultTableName, nameof(HistoryRow.MigrationId), "string", "99999999999999_Last1", null);
  }
}

有两次“最后”迁移：

他们的 ID 是经过选择的，所以他们最后运行（“99999999999999”）
两者都调用自定义代码，该代码
• 必须是幂等的
每个人都从历史表中删除另一个人
他们使用
• Task.Run

   进行异步而非同步

在每次运行期间，一个或另一个运行自定义代码，并从历史表中删除另一个。在下一次运行中，将会发生相反的情况。

相同的双重设置可用于预迁移挂钩。

repo 上有一个未完成的积压项目。

Answer 2

这可以通过扩展标准 EFCore 迁移器实现来实现：

public class CustomMigrator : Migrator
{
    public GenericMigrator(
        IMigrationsAssembly migrationsAssembly, 
        IHistoryRepository historyRepository, 
        IDatabaseCreator databaseCreator, 
        IMigrationsSqlGenerator migrationsSqlGenerator, 
        IRawSqlCommandBuilder rawSqlCommandBuilder, 
        IMigrationCommandExecutor migrationCommandExecutor, 
        IRelationalConnection connection, 
        ISqlGenerationHelper sqlGenerationHelper, 
        ICurrentDbContext currentContext, 
        IModelRuntimeInitializer modelRuntimeInitializer, 
        IDiagnosticsLogger<DbLoggerCategory.Migrations> logger, 
        IRelationalCommandDiagnosticsLogger commandLogger, 
        IDatabaseProvider databaseProvider) : base(migrationsAssembly, historyRepository, databaseCreator, migrationsSqlGenerator, rawSqlCommandBuilder, migrationCommandExecutor, connection, sqlGenerationHelper, currentContext, modelRuntimeInitializer, logger, commandLogger, databaseProvider)
    {
        _connection = connection;
    }

    IRelationalConnection _connection;

    public override void Migrate(string? targetMigration = null)
    {
        base.Migrate(targetMigration);
        if (!_connection.DbConnection.State.HasFlag(ConnectionState.Open))
        {
            _connection.Open();
        }
        using var command = _connection.DbConnection.CreateCommand();
        command.CommandText = "create or replace view v_aaa as select 1 as aaa";
        command.ExecuteNonQuery();
    }

    public override async Task MigrateAsync(string? targetMigration = null, CancellationToken cancellationToken = default)
    {
        await base.MigrateAsync(targetMigration, cancellationToken);
        if (!_connection.DbConnection.State.HasFlag(ConnectionState.Open))
        {
            await _connection.OpenAsync(cancellationToken);
        }
        using var command = _connection.DbConnection.CreateCommand();
        command.CommandText = "create or replace view v_aaa as select 1 as aaa";
        await command.ExecuteNonQueryAsync();
    }
}

该服务应替换如下：

builder.Services.AddDbContext<TDbContext>(options =>
{
    options.UseNpgsql(builder.Configuration.GetConnectionString(connectionStringName));
    options.ReplaceService<IMigrator, CustomMigrator>();
});