Question

我正在使用dotnet ef migrations add {MigrationName}来创建新的迁移。

如果没有实体/上下文更改，则会创建一个包含空Up(MigrationBuilder migrationBuilder)和Down(MigrationBuilder migrationBuilder)函数的迁移。

migrations add命令是否有办法跳过创建＆＃39;空＆＃39;文件？

或者，有没有办法在运行migrations add命令之前检测是否有变化？

Answer 1

我找到了解决这个问题的方法。

有一种方法create migrations programmatically而不是使用CLI。

查看MigrationsScaffolder source code后，我设法修改了第一个链接中的代码，以满足我的需求：

        using (var db = new MyDbContext())
        {
            var reporter = new OperationReporter(
                new OperationReportHandler(
                    m => Console.WriteLine("  error: " + m),
                    m => Console.WriteLine("   warn: " + m),
                    m => Console.WriteLine("   info: " + m),
                    m => Console.WriteLine("verbose: " + m)));

            var designTimeServices = new ServiceCollection()
                .AddSingleton(db.GetService<IHistoryRepository>())
                .AddSingleton(db.GetService<IMigrationsIdGenerator>())
                .AddSingleton(db.GetService<IMigrationsModelDiffer>())
                .AddSingleton(db.GetService<IMigrationsAssembly>())
                .AddSingleton(db.Model)
                .AddSingleton(db.GetService<ICurrentDbContext>())
                .AddSingleton(db.GetService<IDatabaseProvider>())
                .AddSingleton<MigrationsCodeGeneratorDependencies>()
                .AddSingleton<ICSharpHelper, CSharpHelper>()
                .AddSingleton<CSharpMigrationOperationGeneratorDependencies>()
                .AddSingleton<ICSharpMigrationOperationGenerator, CSharpMigrationOperationGenerator>()
                .AddSingleton<CSharpSnapshotGeneratorDependencies>()
                .AddSingleton<ICSharpSnapshotGenerator, CSharpSnapshotGenerator>()
                .AddSingleton<CSharpMigrationsGeneratorDependencies>()
                .AddSingleton<IMigrationsCodeGenerator, CSharpMigrationsGenerator>()
                .AddSingleton<IOperationReporter>(reporter)
                .AddSingleton<MigrationsScaffolderDependencies>()
                .AddSingleton<ISnapshotModelProcessor, SnapshotModelProcessor>()
                .AddSingleton<MigrationsScaffolder>()
                .BuildServiceProvider();

            var scaffolderDependencies = designTimeServices.GetRequiredService<MigrationsScaffolderDependencies>();

            var modelSnapshot = scaffolderDependencies.MigrationsAssembly.ModelSnapshot;
            var lastModel = scaffolderDependencies.SnapshotModelProcessor.Process(modelSnapshot?.Model);
            var upOperations = scaffolderDependencies.MigrationsModelDiffer.GetDifferences(lastModel, scaffolderDependencies.Model);
            var downOperations = upOperations.Any() ? scaffolderDependencies.MigrationsModelDiffer.GetDifferences(scaffolderDependencies.Model, lastModel) : new List<MigrationOperation>();

            if (upOperations.Count() > 0 || downOperations.Count() > 0)
            {
                var scaffolder = designTimeServices.GetRequiredService<MigrationsScaffolder>();

                var migration = scaffolder.ScaffoldMigration(
                    "MyMigration",
                    "MyApp.Data");

                File.WriteAllText(
                    migration.MigrationId + migration.FileExtension,
                    migration.MigrationCode);
                File.WriteAllText(
                    migration.MigrationId + ".Designer" + migration.FileExtension,
                    migration.MetadataCode);
                File.WriteAllText(migration.SnapshotName + migration.FileExtension,
                   migration.SnapshotCode);
            }
        }

Answer 2

我不知道它是否可能，但空迁移也很有用，就像你想手动运行任何脚本一样，例如，创建/改变StoredProcedures / Trigger。为此，您可以专门为特定目的生成空迁移。

dotnet ef迁移添加：仅在存在更改时创建迁移文件

2 个答案: