EF 代码首次迁移答案

【问题标题】：EF code first migrationEF 代码首次迁移
【发布时间】：2013-08-22 14:55:53
【问题描述】：

我已按照以下步骤使用代码优先方法创建数据库。

创建类
启动包管理器
启用迁移 -ContextTypeName -MyDb
在模型类中进行了更改
执行“更新数据库-详细”
更改已反映在数据库表中

现在我连接到数据库并删除表。当我执行“Update-Database -Verbose”命令时，我的期望是它会再次创建表，但它会失败并显示以下错误消息。

    PM> Update-Database -Force
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No pending code-based migrations.
Applying automatic migration: 201308221453295_AutomaticMigration.
System.Data.SqlClient.SqlException (0x80131904): Either the parameter @objname is ambiguous or the claimed @objtype (COLUMN) is wrong.
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
   at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
   at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async, Int32 timeout)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at System.Data.Entity.Migrations.DbMigrator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements(IEnumerable`1 migrationStatements)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, XDocument targetModel, IEnumerable`1 operations, Boolean downgrading, Boolean auto)
   at System.Data.Entity.Migrations.DbMigrator.AutoMigrate(String migrationId, XDocument sourceModel, XDocument targetModel, Boolean downgrading)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.AutoMigrate(String migrationId, XDocument sourceModel, XDocument targetModel, Boolean downgrading)
   at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
   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.RunCore()
   at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run()
ClientConnectionId:d07c8463-88f6-44fa-a242-fe0da2c36f31
Either the parameter @objname is ambiguous or the claimed @objtype (COLUMN) is wrong.

Can anyone help?  How can I create table again using code first approach?

问候， Hemant Shelar

【问题讨论】：

在您的项目中启用迁移并关注其相关文章，如下所示：msdn.microsoft.com/en-us/data/jj591621.aspx

标签： entity-relationship entity-framework-migrations

【解决方案1】：

数据库中有一个系统表包含所有运行迁移，因此重新运行 Update-Database 不应该做任何事情。除非您更改项目中的模型导致自动迁移，否则您没有显式创建迁移并且实体框架正在尝试将数据库与模型匹配。

正如 Raphaël 所说，代码优先。如果您想首先通过代码管理表格，则不应直接修改表格。如果你真的想这样做，你需要从__MigrationHistory系统表中删除迁移，这样Entity Framework就不会认为迁移已经运行了。或使用Update-Database -Target:[migration target here] 通过命令行开关降级/还原数据库。

【讨论】：