EF6

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我正在使用实体框架6，我正在使用迁移。我已经使用初始迁移创建了数据库。现在我已经对模型做了修改，并且上下文已经改变了，我想要更新数据库BUT ... 当我再次尝试运行数据库更新命令种子也在运行，这会导致错误，因为一些数据被再次插入。

I'm Using Entity Framework 6 and I'm using migrations. I have already created the database using an initial migration. Now I have done changes to the Model and the context has changed, and I want to update the database BUT... When I try to run again the Database-Update command the seeds are also running too, and this bring errores due some data is inserted again.

很难相信EF没有任何简单的选项，如 -No-Seed 。

It is hard to believe that EF doesn't have any simple option like -No-Seed for that. I'm almost secure that other ORMs does.

推荐答案

从源代码 DbMigrationsConfiguration< TContext> ：

/// <summary> /// Runs after upgrading to the latest migration to allow seed data to be updated. /// /// </summary> /// /// <remarks> /// Note that the database may already contain seed data when this method runs. This means that /// implementations of this method must check whether or not seed data is present and/or up-to-date /// and then only make changes if necessary and in a non-destructive way. The /// <see cref="M:System.Data.Entity.Migrations.DbSetMigrationsExtensions.AddOrUpdate``1(System.Data.Entity.IDbSet{``0},``0[])"/> /// can be used to help with this, but for seeding large amounts of data it may be necessary to do less /// granular checks if performance is an issue. /// If the <see cref="T:System.Data.Entity.MigrateDatabaseToLatestVersion`2"/> database /// initializer is being used, then this method will be called each time that the initializer runs. /// If one of the <see cref="T:System.Data.Entity.DropCreateDatabaseAlways`1"/>, <see cref="T:System.Data.Entity.DropCreateDatabaseIfModelChanges`1"/>, /// or <see cref="T:System.Data.Entity.CreateDatabaseIfNotExists`1"/> initializers is being used, then this method will not be /// called and the Seed method defined in the initializer should be used instead. /// /// </remarks> /// <param name="context">Context to be used for updating seed data. </param>

基本上，您没有其他选项来实现添加或更新逻辑，因为种子方法将在使用初始化程序后每次执行。

Basically, you don't have another option than implement an "add or update" logic because the Seed method will be executed each time after the initializer is used.

AddOrUpdate扩展方法对此有用，但在某些情况下，我也使用过：

The AddOrUpdate extension method is useful for this, but I have also used this in some cases:

if (!context.Entities.Any()) { // Seed }