我在我的模型类中进行了一些更改，比如---添加了一些新属性，并根据需求的变化删除了一些...我的旧城市类有以下列
public class City()
{
public int CityId { get; set;}
public string CityName { get; set;}
public decimal Longitude { get; set;}
public decimal Latitude { get; set;}
}
现在，我在City类中进行了一些更改。现在它只包含两个字段---
public class City()
{
public int Id { get; set;}
public string Name { get; set;}
}
现在，我在包管理器控制台中运行这个简单的Add-Migration命令---
PM> Add-Migration ccccxxxx
It runs successfully
然后我在包管理器中尝试了Update-Database命令，它给了我以下错误---
PM> Update-Database
Multiple identity columns specified for table 'Cities'. Only one identity column per table is allowed.
然后我搜索错误并来到这个链接------ http://www.itorian.com/2013/10/multiple-identity-columns-specified-for.html 我按照那里给出的步骤改变了我的VoidUp（）方法，就像这样---
public partial class ccccxxxx : DbMigration
{
public override void Up()
{
DropPrimaryKey("dbo.Cities");
DropColumn("dbo.Cities", "CityId");
DropColumn("dbo.Cities", "CityName");
DropColumn("dbo.Cities", "Latitude");
DropColumn("dbo.Cities", "Longitude");
AddColumn("dbo.Cities", "Id", c => c.Int(nullable: false, identity: true));
AddColumn("dbo.Cities", "Name", c => c.String());
AddPrimaryKey("dbo.Cities", "Id");
}
public override void Down()
{
AddColumn("dbo.Cities", "Longitude", c => c.Decimal(nullable: false, precision: 18, scale: 2));
AddColumn("dbo.Cities", "Latitude", c => c.Decimal(nullable: false, precision: 18, scale: 2));
AddColumn("dbo.Cities", "CityName", c => c.String());
AddColumn("dbo.Cities", "CityId", c => c.Int(nullable: false, identity: true));
DropPrimaryKey("dbo.Cities");
DropColumn("dbo.Cities", "Name");
DropColumn("dbo.Cities", "Id");
AddPrimaryKey("dbo.Cities", "CityId");
}
}
现在，我在包管理器控制台中收到以下错误。令人沮丧的消息---
ALTER TABLE DROP COLUMN failed because 'Longitude' is the only data column in table 'Cities'. A table must have at least one data column.
不知道如何修复这个bug --- 包管理器控制台窗口的详细处理脚本是---
PM> Update-Database
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Applying explicit migrations: [201507211404004_ccccxxxx].
Applying explicit migration: 201507211404004_ccccxxxx.
System.Data.SqlClient.SqlException (0x80131904): ALTER TABLE DROP COLUMN failed because 'Longitude' is the only data column in table 'Cities'. A table must have at least one data column.
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, B 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, Boolean asyncWrite)
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.Infrastructure.Interception.DbCommandDispatcher. <NonQuery>b__0(DbCommand t, DbCommandInterceptionContext`1 c)
at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TTarget,TInterceptionContext,TResult](TTarget target, Func`3 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed)
at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery(DbCommand command, DbCommandInterceptionContext interceptionContext)
at System.Data.Entity.Internal.InterceptableDbCommand.ExecuteNonQuery()
at System.Data.Entity.Migrations.DbMigrator.ExecuteSql(MigrationStatement migrationStatement, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext)
at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ExecuteSql(MigrationStatement migrationStatement, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext)
at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext)
at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinTransaction(IEnumerable`1 migrationStatements, DbTransaction transaction, DbInterceptionContext interceptionContext)
at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinNewTransaction(IEnumerable`1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext)
at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext)
at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbConnection connection)
at System.Data.Entity.Migrations.DbMigrator.<>c__DisplayClass30.<ExecuteStatements>b__2e()
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.<>c__DisplayClass1.<Execute>b__0()
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Action operation)
at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements, DbTransaction existingTransaction)
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, VersionedModel targetModel, IEnumerable`1 operations, IEnumerable`1 systemOperations, Boolean downgrading, Boolean auto)
at System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration)
at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ApplyMigration(DbMigration migration, DbMigration lastMigration)
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.UpdateInternal(String targetMigration)
at System.Data.Entity.Migrations.DbMigrator.<>c__DisplayClassc.<Update>b__b()
at System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase)
at System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase)
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:de580d2c-d99b-4a45-bb88-736c802e5104
ALTER TABLE DROP COLUMN failed because 'Longitude' is the only data c column in table 'Cities'. A table must have at least one data column.
PM>
答案 0 :(得分：0)
将您的Up（）代码更改为此代码，这样您就不会删除每个字段：
public override void Up()
{
AddColumn("dbo.Cities", "Name", c => c.String());
DropPrimaryKey("dbo.Cities");
DropColumn("dbo.Cities", "CityId");
DropColumn("dbo.Cities", "CityName");
DropColumn("dbo.Cities", "Latitude");
DropColumn("dbo.Cities", "Longitude");
AddColumn("dbo.Cities", "Id", c => c.Int(nullable: false, identity: true));
AddPrimaryKey("dbo.Cities", "Id");
}
你的Down（）代码
public override void Down()
{
DropColumn("dbo.Cities", "Id");
AddColumn("dbo.Cities", "Longitude", c => c.Decimal(nullable: false, precision: 18, scale: 2));
AddColumn("dbo.Cities", "Latitude", c => c.Decimal(nullable: false, precision: 18, scale: 2));
AddColumn("dbo.Cities", "CityName", c => c.String());
AddColumn("dbo.Cities", "CityId", c => c.Int(nullable: false, identity: true));
DropPrimaryKey("dbo.Cities");
DropColumn("dbo.Cities", "Name");
AddPrimaryKey("dbo.Cities", "CityId");
}