c# - EF6 - 运行不带种子的更新数据库命令

Question

我正在使用 Entity Framework 6 并且正在使用迁移。我已经使用初始迁移创建了数据库。现在我已经对模型进行了更改并且上下文发生了变化，我想更新数据库但是......当我尝试再次运行 Database-Update 命令时，种子也在运行，并且由于再次插入了一些数据而导致错误。

那么，如何在不运行种子方法的情况下运行 Update-Database 命令？

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很难相信 EF 没有像 -No-Seed 这样的简单选项。我几乎可以肯定其他 ORM 确实如此。

Answer 1

来自DbMigrationsConfiguration<TContext>的源代码:

/// <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，除了实现“添加或更新”逻辑之外别无选择，因为每次使用初始化程序后都会执行 Seed 方法。

AddOrUpdate 扩展方法对此很有用，但我在某些情况下也使用过它:

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