实体框架迁移更新数据库成功，但未添加数据库列

Question

我在带有SQL Server 2008 R2的VS2012中使用实体框架。 我已启用迁移，并且正在向我的数据库类之一（即设计）中添加一个字符串字段（即DropboxUrl）。

// Design.cs

public class Design
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        [StringLength(Constants.DESIGN_NAME_MAX_LENGTH)]
        public string Name { get; set; }

        [StringLength(Constants.DESIGN_DESC_MAX_LENGTH)]
        public string Description { get; set; }

        public ItemDate Dates { get; set; }

        public string DropboxUrl { get; set; } // Added this line
    }

// SedaContext.cs:

public class SedaContext : DbContext
    {
        public DbSet<Company> Companies { get; set; }

        public DbSet<Design> Designs { get; set; }
…
}


// Global.aspx
protected void Application_Start()
        {

            // Application initialize
            // https://stackoverflow.com/questions/3600175/the-model-backing-the-database-context-has-changed-since-the-database-was-crea

            Database.SetInitializer<SedaContext>(null);

在Package Manager控制台中，当我运行PM> update-database时，它抱怨数据库中已经存在一个名为“ Companies”的对象。 “公司”是我试图更新的现有数据库中当前存在的表。

即。

PM> update-database -verbose
Using StartUp project 'UI'.
Using NuGet project 'UI'.
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Target database is: 'SedaDev' (DataSource: ., Provider: System.Data.SqlClient, Origin: Configuration).
No pending explicit migrations.
Applying automatic migration: 201405311730564_AutomaticMigration.
CREATE TABLE [dbo].[Companies] (
    [Id] [uniqueidentifier] NOT NULL DEFAULT newsequentialid(),
    [Name] [nvarchar](max),
    [Description] [nvarchar](max),
    [Owner_UserId] [int],
    CONSTRAINT [PK_dbo.Companies] PRIMARY KEY ([Id])
)
System.Data.SqlClient.SqlException (0x80131904): There is already an object named 'Companies' in the database.
...
   at System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update(String targetMigration)
   at System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.Run()
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Update(String targetMigration, Boolean force)
   at System.Data.Entity.Migrations.UpdateDatabaseCommand.<>c__DisplayClass2.<.ctor>b__0()
   at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
ClientConnectionId:fa9e9e62-aba0-435f-9309-e9fc8fbe19d5

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

尝试1：搜寻此错误后，我遇到了以下解决方法： http : //christesene.com/entity-framework-4-3-code-first-with-automatic-migrations/

建议我先跑步

PM> Add-migration initial

Scaffolding migration 'initial'.
The Designer Code for this migration file includes a snapshot of your current Code First model. This snapshot is used to calculate the changes to your model when you scaffold the next migration. If you make additional changes to your model that you want to include in this migration, then you can re-scaffold it by running 'Add-Migration initial' again.

并删除了Up / Down方法：

即。 我可以看到DropboxUrl是Up方法中的一个字段，但是我按照建议将其删除。

public override void Up()
        {
/*
    CreateTable(
                "dbo.Companies",
                c => new
                    {
                        Id = c.Guid(nullable: false, identity: true),
                        Name = c.String(),
                        Description = c.String(),
                        Owner_UserId = c.Int(),
                    })
                .PrimaryKey(t => t.Id)
                .ForeignKey("dbo.UserProfiles", t => t.Owner_UserId)
                .Index(t => t.Owner_UserId);
...
  CreateTable(                "dbo.Designs",
                c => new
                    {
                        Id = c.Guid(nullable: false, identity: true),
                        Name = c.String(maxLength: 100),
                        Description = c.String(maxLength: 1000),
                        Dates_Create = c.DateTime(nullable: false),
                        Dates_LastUpdate = c.DateTime(nullable: false),
                        DropboxUrl = c.String(),
                        Project_Id = c.Guid(),
                    })
                .PrimaryKey(t => t.Id)
                .ForeignKey("dbo.Projects", t => t.Project_Id)
                .Index(t => t.Project_Id);
*/
        }

之后，我再次运行update-database，它似乎成功。

PM> update-database -verbose
Using StartUp project 'UI'.
Using NuGet project 'UI'.
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Target database is: 'SedaDev' (DataSource: phobos.spxis.com, Provider: System.Data.SqlClient, Origin: Configuration).
Applying explicit migrations: [201406020449030_initial].
Applying explicit migration: 201406020449030_initial.
INSERT [dbo].[__MigrationHistory]([MigrationId], [ContextKey], [Model], [ProductVersion])

VALUES (N'201406020449030_initial', N'Delecs.Seda.DataAccess.Migrations.Configuration',  0x1F8B0800000000000400ED1DCB72DCB8F19EAAFCC3D49C92544523D9F166
...
7B7C117028FAD9D8632C54E5F87C13A0D36590D83B7A73FA9F8AD368F7FFE3F0347EA807B340100 , N'6.0.2-21211')
Running Seed method

问题1：更新后我的表未更改（即，代码中存在的DropboxUrl列未添加到数据库）。

问题2：而且我也无法使数据库恢复到初始状态：

即。

PM> update-database -TargetMigration $InitialDatabase
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Reverting migrations: [201406020449030_initial].
Reverting automatic migration: 201406020449030_initial.
Automatic migration was not applied because it would result in data loss.
PM> update-database -TargetMigration $InitialDatabase -force
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Reverting migrations: [201406020449030_initial].
Reverting automatic migration: 201406020449030_initial.
System.Data.SqlClient.SqlException (0x80131904): Could not drop object 'dbo.UserProfiles' because it is referenced by a FOREIGN KEY constraint.

尝试2：添加迁移时，我还尝试使用-IgnoreChanges标志： ASP.NET SimpleMembershipProvider的自动迁移

PM> Add-migration initial -IgnoreChanges
Re-scaffolding migration 'initial'.

PM> update-database -verbose

同样，我看到了同样的事情，更新数据库成功了，但是数据库列DropboxUrl没有添加到Designs表中。 但是，如果我创建一个新数据库，则DropboxUrl列将按预期方式显示。

问题：在更新数据库时，如何解决数据库错误中已经存在名为“ Companies”的对象，并且仍然成功添加我的列的问题？ 看来这应该是可行的基本方案。

谢谢。

Answer 1

当您在迁移中注释掉Up（）和Down（）方法时，您删除了添加数据库列的代码。

您应该按以下方式更改Up（）和Down（）：

public override void Up() {
   AddColumn("Companies", "DropboxUrl", x => x.String());
}

public override void Down() {
    DropColumn("Companies", "DropboxUrl");
}

为了使Entity Framework将来能够为您解决这个问题，您需要进行一次初始迁移，以使其了解在将属性添加到代码之前已经存在一个表。 例如Add-Migration -force -ignore.

然后，您添加该列并转到Add-Migration AddedDropboxUrlColumn ，它将如我在新迁移中所描述的那样生成Up（）和Down（）方法。