实体框架，自动应用迁移 [英] Entity Framework, Automatic apply Migrations

问题描述

我正在使用 AutomaticMigrationsEnabled = true 的实体框架代码优先方法：

I am using Entity Framework Code First approach with AutomaticMigrationsEnabled = true:

Database.SetInitializer(new MigrateDatabaseToLatestVersion<DbContext, MigrateDBConfiguration>());
//////////////////////////////////

public class MigrateDBConfiguration : System.Data.Entity.Migrations.DbMigrationsConfiguration<DbContext>
{
    public MigrateDBConfiguration()
    {
        AutomaticMigrationsEnabled = true;
        AutomaticMigrationDataLossAllowed = true;
    }
}

项目的第一次运行将创建数据库和表如预期的那样。通过添加或删除字段更改模型后，我运行了添加迁移。生成了Migration类，但在运行项目后发生此异常：

The first run of the project creates the database and tables as expected. After changing my model by adding or dropping fields, I ran Add-Migration. The Migration class was generated but after running the project this exception occurs:

在EntityFramework.dll中发生了类型为'System.InvalidOperationException'的异常。

An exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll but was not handled in user code

其他信息：自创建数据库以来，支持 DBContext上下文的模型已更改了
。

Additional information: The model backing the 'DBContext' context has changed since the database was created.

编辑：根据 arturo menchaca 我这样更改了代码：

Per the guidance in the answer of arturo menchaca I changed my code like this:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        Database.SetInitializer(new MigrateDatabaseToLatestVersion<DBContext, MigrateDBConfiguration<DBContext>>());

...

更改后会发生此异常：

数据库中已经有一个名为 MyTable的对象。

There is already an object named 'MyTable' in the database.

如何应用数据库迁移？

推荐答案

最后，我找到了解决问题的方法。我在每个应用程序开始时都调用此方法：

Finally, I found a solution to my problem. I call this method in each application start :

public void InitializeDatabase(DataAccessManager context)
{
    if (!context.Database.Exists() || !context.Database.CompatibleWithModel(false))
    {
        var configuration = new DbMigrationsConfiguration();
        var migrator = new DbMigrator(configuration);
        migrator.Configuration.TargetDatabase = new DbConnectionInfo(context.Database.Connection.ConnectionString, "System.Data.SqlClient");
        var migrations = migrator.GetPendingMigrations();
        if (migrations.Any())
        {
            var scriptor = new MigratorScriptingDecorator(migrator);
            var script = scriptor.ScriptUpdate(null, migrations.Last());

            if (!string.IsNullOrEmpty(script))
            {
                context.Database.ExecuteSqlCommand(script);
            }
        }
    }
}

这篇关于实体框架，自动应用迁移的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！