C# 已经有一个名为'；员工'；在数据库中

我尝试更新数据库，但出现以下错误：

数据库中已存在名为“Employee”的对象

这是我的最后一个迁移文件：

 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; }
    }

堆栈跟踪：

[SqlException（0x80131904）：已经有一个名为 数据库中的“雇员”。]
System.Data.SqlClient.SqlConnection.OnError（SqlException异常， 布尔断开连接，操作

1 wrapCloseInAction）+2418102

System.Data.SqlClient.SqlInternalConnection.OnError（SqlException
异常，布尔断开连接，操作

1 wrapCloseInAction） +5694456 System.Data.SqlClient.TdsParser.ThroweException和Warning（TdsParserStateObject stateObj，布尔调用方连接锁，布尔异步关闭）+285
System.Data.SqlClient.TdsParser.TryRun（运行行为， SqlCommand cmdHandler、SqlDataReader数据流、， BulkCopySimpleResultSet bulkCopyHandler，TdsParserStateObject stateObj、Boolean和dataReady）+3731
System.Data.SqlClient.SqlCommand.RunExecuteOnQueryTds（字符串 methodName，布尔异步，Int32超时，布尔异步写入）+959
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery（TaskCompletionSource

1
完成，字符串方法名，布尔sendToPipe，Int32超时，
布尔异步写入）+272

System.Data.SqlClient.SqlCommand.ExecuteNonQuery（）+280

System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.b__0（DbCommand
t、 DbCommandInterceptionContext

1c）+36
System.Data.Entity.Infrastructure.InternalDispatcher

1.Dispatch（TTarget
目标，函数

3操作，TInterceptionContext拦截context， 动作

3执行，动作
3执行）+138

System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery（DbCommand
命令，dbcommandinterceptoncontext interceptoncontext）+476

System.Data.Entity.Internal.InterceptableDbCommand.ExecuteOnQuery（）
+177 System.Data.Entity.Migrations.Dbmigator.ExecuteSql（MigrationStatement
迁移语句、数据库连接、数据库事务
事务，dbinterceptoncontext interceptoncontext）+194

System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteSql（MigrationStatement
迁移语句、数据库连接、数据库事务
事务，dbinterceptoncontext interceptoncontext）+62

System.Data.Entity.Migrations.Dbmigator.ExecuteStatementInternal（IEnumerable
1
迁移语句、数据库连接、数据库事务
事务，dbinterceptoncontext interceptoncontext）+113

System.Data.Entity.Migrations.Dbmigator.ExecuteStatementSwithintTransaction（IEnumerable
1
迁移语句、DbTransaction事务、DbInterceptionContext
拦截上下文）+110

System.Data.Entity.Migrations.Dbmigator.ExecuteStatementSwitthingTransaction（IEnumerable
1
迁移语句、数据库连接、数据库拦截上下文
拦截上下文）+172

System.Data.Entity.Migrations.Dbmigator.ExecuteStatementInternal（IEnumerable
1
迁移语句、数据库连接、数据库拦截上下文
拦截上下文）+429

System.Data.Entity.Migrations.Dbmigator.ExecuteStatementInternal（IEnumerable
1
迁移语句，数据库连接）+646

System.Data.Entity.Migrations.c__DisplayClass30.b__2e（）
+66 System.Data.Entity.SqlServer.c__DisplayClass1.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.Dbmigator.ExecuteStatements（IEnumerable
1
迁移语句，DbTransaction existingTransaction）+327

System.Data.Entity.Migrations.DbMigrator.ExecuteStatements（IEnumerable
1
迁移状态）+39

System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements（IEnumerable
1
迁移状态）+42

System.Data.Entity.Migrations.DbMigrator.ExecuteOperations（字符串
migrationId，VersionedModel targetModel，IEnumerable
1操作，
IEnumerable
1系统操作、布尔降级、布尔自动）
+1372 System.Data.Entity.Migrations.DbMigrator.ApplyMigration（DbMigration
迁移，DbMigration lastMigration）+783

System.Data.Entity.Migrations.Infrastructure.MigratorBase.ApplyMigration（DbMigration
迁移，DbMigration lastMigration）+56

System.Data.Entity.Migrations.DbMigrator.Upgrade（IEnumerable
1
pendingMigrations，字符串targetMigrationId，字符串lastMigrationId）
+192 System.Data.Entity.Migrations.Infrastructure.MigratorBase.Upgrade（IEnumerable
1
pendingMigrations，字符串targetMigrationId，字符串lastMigrationId）
+59 System.Data.Entity.Migrations.Dbmigator.UpdateInternal（字符串targetMigration）+888

System.Data.Entity.Migrations.c__DisplayClassc.b__b（）+38

System.Data.Entity.Migrations.Dbmigator.EnsureDatabaseExists（操作
必须成功访问数据库）+516

System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists（操作
必须成功访问数据库）+42

System.Data.Entity.Migrations.DbMigrator.Update（字符串
targetMigration）+136

System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update（）+33
System.Data.Entity.Internal.DatabaseCreator.CreateDatabase（InternalContext
internalContext，Func
3 createMigrator，ObjectContext）
+175 System.Data.Entity.Internal.InternalContext.CreateDatabase（ObjectContext
objectContext，DatabaseExistenceEstate）+150

System.Data.Entity.Database.Create（DatabaseExistenceEstate
ExistenceEstate）+444

System.Data.Entity.DropCreateDatabaseAlways
1.InitializeDatabase（TContext
上下文）+158

System.Data.Entity.Internal.c_显示
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;
            }
        }

    }