数据库中已经有一个名为“ Employee”的对象

Question

我尝试更新数据库，但出现此错误：

数据库中已经有一个名为“ Employee”的对象。

这是我的上一个迁移文件：

 public partial class explain : DbMigration
    {
        public override void Up()
        {
            DropForeignKey("dbo.Employee", "Person_PersonId", "dbo.Person");
            DropForeignKey("dbo.Receptionist", "PersonId", "dbo.Employee");
            DropIndex("dbo.Employee", new[] { "Person_PersonId" });
            CreateTable(
                "dbo.Employee",
                c => new
                    {
                        PersonId = c.Int(nullable: false),
                        Receptionist_PersonId = c.Int(),
                        Salary = c.Int(nullable: false),
                        Hiredate = c.DateTime(nullable: false),
                        isManager = c.Boolean(nullable: false),
                    })
                .PrimaryKey(t => t.PersonId)
                .ForeignKey("dbo.Person", t => t.PersonId)
                .ForeignKey("dbo.Receptionist", t => t.Receptionist_PersonId)
                .Index(t => t.PersonId)
                .Index(t => t.Receptionist_PersonId);

            AddForeignKey("dbo.Receptionist", "PersonId", "dbo.Employee", "PersonId");
            DropTable("dbo.Employee");
        }

        public override void Down()
        {
            CreateTable(
                "dbo.Employee",
                c => new
                    {
                        PersonId = c.Int(nullable: false),
                        Salary = c.Int(nullable: false),
                        Hiredate = c.DateTime(nullable: false),
                        isManager = c.Boolean(nullable: false),
                        Person_PersonId = c.Int(nullable: false),
                    })
                .PrimaryKey(t => t.PersonId);

            DropForeignKey("dbo.Employee", "Receptionist_PersonId", "dbo.Receptionist");
            DropForeignKey("dbo.Receptionist", "PersonId", "dbo.Employee");
            DropForeignKey("dbo.Employee", "PersonId", "dbo.Person");
            DropIndex("dbo.Employee", new[] { "Receptionist_PersonId" });
            DropIndex("dbo.Employee", new[] { "PersonId" });
            DropTable("dbo.Employee");
            CreateIndex("dbo.Employee", "Person_PersonId");
            AddForeignKey("dbo.Receptionist", "PersonId", "dbo.Employee", "PersonId");
            AddForeignKey("dbo.Employee", "Person_PersonId", "dbo.Person", "PersonId");
        }
    }

Employee.cs模型

public class Employee : Person
    {
        public Employee()
        {
            EmployeeSchedule = new HashSet<EmployeeSchedule>();
            Vacation = new HashSet<Vacation>();
        }

        [Required]
        [Display(Name = "Wynagrodzenie")]
        public int Salary { get; set; }

        [Required]
        [Display(Name = "Data zatrudnienia")]
        public DateTime Hiredate { get; set; }

        [Display(Name = "Kierownik")]
        public bool isManager { get; set; }

        public virtual ICollection<EmployeeSchedule> EmployeeSchedule { get; set; }

        public virtual Lifeguard Lifeguard { get; set; }

        public virtual Receptionist Receptionist { get; set; }

        public virtual Trainer Trainer { get; set; }
        public virtual ICollection<Vacation> Vacation { get; set; }
    }

人.cs

public abstract class Person
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int PersonId { get; set; }

        [Required]
        public long Pesel { get; set; }

        [Required]
        [StringLength(30, ErrorMessage = "Imię nie może zawierać więcej niż 30 znaków.")]
        [Display(Name = "Imię")]
        public string FirstName { get; set; }

        [Required]
        [StringLength(60, ErrorMessage = "Nazwisko nie może zawierać wiecej niż 60 znaków.")]
        [Display(Name = "Nazwisko")]
        public string LastName { get; set; }

        [Required]
        [EmailAddress(ErrorMessage = "Błędny format adresu e-mail.")]
        public string Email { get; set; }

        [Required]
        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)]
        [Display(Name = "Data urodzenia")]
        public DateTime DateOfBirth  { get; set; }
        [NotMapped]
        public int age;
        [NotMapped]
        public int Age
        {
            get
            {
                DateTime today = DateTime.Today;
                age = today.Year - DateOfBirth.Year;
                if (DateOfBirth > today.AddYears(-age))
                {
                    age--;
                }
                return age;
            }
        }

        [NotMapped]
        [Display(Name="Imię i Nazwisko")]
        public string FullName
        {
            get
            {
                return FirstName + " " + LastName;
            }
        }

    }

堆栈跟踪：

[SqlException（0x80131904）：数据库中已经有一个名为“ Employee”的对象。
System.Data.SqlClient.SqlConnection.OnError（SqlException异常，布尔值breakConnection，操作1 wrapCloseInAction) +2418102
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action 1 wrapCloseInAction) +2418102
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action 1 wrapCloseInAction) +2418102
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action 1 wrapCloseInAction）+5694456 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning（TdsParserStateObject stateObj，布尔值调用程序HasConnectionLock，布尔值asyncClose）+285
System.Data.SqlClient.TdsParser.TryRun（RunBehavior runBehavior，SqlCommand cmdHandler，SqlDataReader dataStream，BulkCopySimpleResultSet bulkCopyHandler，TdsParserStateObject stateObj，Boolean＆dataReady）+3731
System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds（字符串methodName，布尔异步，Int32超时，布尔asyncWrite）+959
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery（TaskCompletionSource 1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) +272
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +280
System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.<NonQuery>b__0(DbCommand t, DbCommandInterceptionContext 1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) +272
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +280
System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.<NonQuery>b__0(DbCommand t, DbCommandInterceptionContext 1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) +272
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +280
System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.<NonQuery>b__0(DbCommand t, DbCommandInterceptionContext 1 c）+36
System.Data.Entity.Infrastructure.Interception.InternalDispatcher 1.Dispatch(TTarget target, Func 3操作，TInterceptionContext拦截上下文， 3 executing, Action 3，执行3 executing, Action 3）+138
System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery（DbCommand命令，DbCommandInterceptionContext拦截上下文）+476
System.Data.Entity.Internal.InterceptableDbCommand.ExecuteNonQuery（）+177 System.Data.Entity.Migrations.DbMigrator.ExecuteSql（MigrationStatement migrationStatement，DbConnection连接，DbTransaction事务，DbInterceptionContext拦截上下文）+194
System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteSql（MigrationStatement migrationStatement，DbConnection连接，DbTransaction事务，DbInterceptionContext拦截上下文）+62
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal（IEnumerable 1 migrationStatements, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) +113
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinTransaction(IEnumerable 1 migrationStatements, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) +113
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinTransaction(IEnumerable 1 migrationStatements, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) +113
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinTransaction(IEnumerable 1 migrationStatements，DbTransaction事务，DbInterceptionContext拦截上下文）+110
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinNewTransaction（IEnumerable 1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext) +172
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable 1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext) +172
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable 1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext) +172
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable 1 migrationStatements，DbConnection连接，DbInterceptionContext拦截上下文）+429
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal（IEnumerable 1 migrationStatements, DbConnection connection) +646
System.Data.Entity.Migrations.<>c__DisplayClass30.<ExecuteStatements>b__2e() +66 System.Data.Entity.SqlServer.<>c__DisplayClass1.<Execute>b__0() +34 System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func 1 migrationStatements, DbConnection connection) +646
System.Data.Entity.Migrations.<>c__DisplayClass30.<ExecuteStatements>b__2e() +66 System.Data.Entity.SqlServer.<>c__DisplayClass1.<Execute>b__0() +34 System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func 1 migrationStatements, DbConnection connection) +646
System.Data.Entity.Migrations.<>c__DisplayClass30.<ExecuteStatements>b__2e() +66 System.Data.Entity.SqlServer.<>c__DisplayClass1.<Execute>b__0() +34 System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func 1操作）+251
System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute（操作操作）+196
System.Data.Entity.Migrations.DbMigrator.ExecuteStatements（IEnumerable 1 migrationStatements, DbTransaction existingTransaction) +327
System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable 1 migrationStatements, DbTransaction existingTransaction) +327
System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable 1 migrationStatements, DbTransaction existingTransaction) +327
System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable 1 migrationStatements）+39
System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements（IEnumerable 1 migrationStatements) +42
System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, VersionedModel targetModel, IEnumerable 1 migrationStatements) +42
System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, VersionedModel targetModel, IEnumerable 1 migrationStatements) +42
System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, VersionedModel targetModel, IEnumerable 1操作，IEnumerable 1 systemOperations, Boolean downgrading, Boolean auto) +1372 System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration) +783
System.Data.Entity.Migrations.Infrastructure.MigratorBase.ApplyMigration(DbMigration migration, DbMigration lastMigration) +56
System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable 1 systemOperations, Boolean downgrading, Boolean auto) +1372 System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration) +783
System.Data.Entity.Migrations.Infrastructure.MigratorBase.ApplyMigration(DbMigration migration, DbMigration lastMigration) +56
System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable 1 systemOperations, Boolean downgrading, Boolean auto) +1372 System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration) +783
System.Data.Entity.Migrations.Infrastructure.MigratorBase.ApplyMigration(DbMigration migration, DbMigration lastMigration) +56
System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable 1endingMigrations，字符串targetMigrationId，字符串lastMigrationId）+192 System.Data.Entity.Migrations.Infrastructure.MigratorBase.Upgrade（IEnumerable 1 pendingMigrations, String targetMigrationId, String lastMigrationId) +59 System.Data.Entity.Migrations.DbMigrator.UpdateInternal(String targetMigration) +888
System.Data.Entity.Migrations.<>c__DisplayClassc.<Update>b__b() +38
System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) +516
System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) +42
System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration) +136
System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update() +33 System.Data.Entity.Internal.DatabaseCreator.CreateDatabase(InternalContext internalContext, Func 1 pendingMigrations, String targetMigrationId, String lastMigrationId) +59 System.Data.Entity.Migrations.DbMigrator.UpdateInternal(String targetMigration) +888
System.Data.Entity.Migrations.<>c__DisplayClassc.<Update>b__b() +38
System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) +516
System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) +42
System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration) +136
System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update() +33 System.Data.Entity.Internal.DatabaseCreator.CreateDatabase(InternalContext internalContext, Func 1 pendingMigrations, String targetMigrationId, String lastMigrationId) +59 System.Data.Entity.Migrations.DbMigrator.UpdateInternal(String targetMigration) +888
System.Data.Entity.Migrations.<>c__DisplayClassc.<Update>b__b() +38
System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) +516
System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) +42
System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration) +136
System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update() +33 System.Data.Entity.Internal.DatabaseCreator.CreateDatabase(InternalContext internalContext, Func 3 createMigrator，ObjectContext objectContext）+175 System.Data.Entity.Internal.InternalContext .CreateDatabase（ObjectContext objectContext，DatabaseExistenceState existState）+150
System.Data.Entity.Database.Create（DatabaseExistenceState existState）+444
System.Data.Entity.DropCreateDatabaseAlways 1.InitializeDatabase(TContext context) +158
System.Data.Entity.Internal.<>c__DisplayClassf 1.InitializeDatabase(TContext context) +158
System.Data.Entity.Internal.<>c__DisplayClassf 1.InitializeDatabase(TContext context) +158
System.Data.Entity.Internal.<>c__DisplayClassf 1.b__e（）+165 System.Data.Entity.Internal.InternalContext.PerformInitializationAction（Action操作）+110
System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization（）+660 System.Data.Entity.Internal.LazyInternalContext.b__4（InternalContext c）+31
System.Data.Entity.Internal.RetryAction 1.PerformAction(TInput input) +143 System.Data.Entity.Internal.LazyInternalContext.InitializeDatabaseAction(Action 1动作）+292
System.Data.Entity.Internal.LazyInternalContext.InitializeDatabase（）+123 System.Data.Entity.Internal.InternalContext.Initialize（）+42 System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType（Type entityType）+39
System.Data.Entity.Internal.Linq.InternalSet 1.Initialize() +137
System.Data.Entity.Internal.Linq.InternalSet 1.Initialize() +137
System.Data.Entity.Internal.Linq.InternalSet 1.Initialize() +137
System.Data.Entity.Internal.Linq.InternalSet 1.get_InternalContext（）+38 System.Data.Entity.Internal.Linq.InternalSet 1.FindAsync(CancellationToken cancellationToken, Object[] keyValues) +58
System.Data.Entity.DbSet 1.FindAsync(CancellationToken cancellationToken, Object[] keyValues) +58
System.Data.Entity.DbSet 1.FindAsync(CancellationToken cancellationToken, Object[] keyValues) +58
System.Data.Entity.DbSet 1.FindAsync（CancellationToken cancelleToken，Object [] keyValues）+70
System.Data.Entity.DbSet 1.FindAsync(Object[] keyValues) +69
Microsoft.AspNet.Identity.EntityFramework.EntityStore 1.FindAsync(Object[] keyValues) +69
Microsoft.AspNet.Identity.EntityFramework.EntityStore 1.FindAsync(Object[] keyValues) +69
Microsoft.AspNet.Identity.EntityFramework.EntityStore 1.GetByIdAsync（Object id）+104
Microsoft.AspNet.Identity.EntityFramework.d__6c.MoveNext（）+275 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter 1.GetResult() +28 Microsoft.AspNet.Identity.CultureAwaiter 1.GetResult（） 1.GetResult() +28 Microsoft.AspNet.Identity.CultureAwaiter 123 Microsoft.AspNet.Identity.Owin 。<b__1> d__4.MoveNext（）+1519 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.Owin.Security.Cookies.d__2.MoveNext（）+3729 System.Runtime.CompilerServices.TaskAwaiter .ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter`1.GetResult（）+28 Microsoft.Owin.Security.Infrastructure.d__0.MoveNext（）+810 System.Runtime.CompilerServices .TaskAwaiter.ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.Owin.Security.Infrastructure.d__0.MoveNext（）+427 System.Runtime.CompilerServices.TaskAwaiter .ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.AspNet.Identity.Owin.d__0.MoveNext（）+641 System.Runtime.CompilerServices.TaskAwaiter。 .ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.AspNet.Identity.Owin.d__0.MoveNext（）+641 System.Runtime.CompilerServices.TaskAwaiter。 .ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.AspNet.Identity.Owin.d__0.MoveNext（）+641 System.Runtime.CompilerServices.TaskAwaiter。 .ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.AspNet.Identity.Owin.d__0.MoveNext（）+641 System.Runtime.CompilerServices.TaskAwaiter。 .ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.d__5.MoveNext（）+287 System.Runtime.CompilerServices .TaskAwaiter.ThrowForNonSuccess（任务任务）+99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）+58 System.Runtime.CompilerServices.TaskAwaiter.GetResult（）+26 Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.d__2.MoveNext（）+272 System.Runtime.ExceptionServices .ExceptionDispatchInfo.Throw（）+26 Microsoft.Owin.Host.SystemWeb.Infrastructure.ErrorState.Rethrow（）+33 Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.StageAsyncResult.End（IAsyncResult ar）+150
Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.EndFinalWork（IAsyncResult ar）+42
System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute（）+380 System.Web.HttpApplication.ExecuteStep（IExecutionStep步骤，布尔值并已完成）+155

Answer 1

尝试在迁移中在创建语句之前将DropTable语句上移。 这样，您可以在创建新员工表之前删除现有员工表。