已有一个名为＆＃39; Employee＆＃39;在数据库中

Question

我尝试更新我的数据库，但是我有这个错误：

  

已有一个名为＆＃39; Employee＆＃39;在数据库中。

这是我上一次迁移文件：

 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; }
    }

Person.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;
            }
        }

    }

堆栈追踪：

  

[SqlException（0x80131904）：已经有一个名为的对象   ＆＃39;员工＆＃39;在数据库中。]
  System.Data.SqlClient.SqlConnection.OnError（SqlException异常，   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，Boolean callerHasConnectionLock，Boolean asyncClose）+285
  System.Data.SqlClient.TdsParser.TryRun（RunBehavior runBehavior，   SqlCommand cmdHandler，SqlDataReader dataStream，   BulkCopySimpleResultSet bulkCopyHandler，TdsParserStateObject   stateObj，布尔＆amp; dataReady）+3731
  System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds（字符串   methodName，Boolean async，Int32 timeout，Boolean 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 c）+36
  System.Data.Entity.Infrastructure.Interception.InternalDispatcher 1.Dispatch(TTarget target, Func 3操作，TInterceptionContext interceptionContext，   行动3 executing, Action 3已执行）+138
  System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery（的DbCommand   command，DbCommandInterceptionContext interceptionContext）+476
  System.Data.Entity.Internal.InterceptableDbCommand.ExecuteNonQuery（）   +177 System.Data.Entity.Migrations.DbMigrator.ExecuteSql（MigrationStatement   migrationStatement，DbConnection连接，DbTransaction   transaction，DbInterceptionContext interceptionContext）+194
  System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteSql（MigrationStatement   migrationStatement，DbConnection连接，DbTransaction   transaction，DbInterceptionContext interceptionContext）+62
  System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal（IEnumerable的1 migrationStatements, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) +113
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinTransaction(IEnumerable 1   migrationStatements，DbTransaction事务，DbInterceptionContext   interceptionContext）+110
  System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinNewTransaction（IEnumerable的1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext) +172
System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable 1   migrationStatements，DbConnection连接，DbInterceptionContext   interceptionContext）+429
  System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal（IEnumerable的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（动作   操作）+196
  System.Data.Entity.Migrations.DbMigrator.ExecuteStatements（IEnumerable的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个操作，   IEnumerable的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   pendingMigrations，String targetMigrationId，String 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 3 createMigrator，ObjectContext objectContext）   +175 System.Data.Entity.Internal.InternalContext.CreateDatabase（ObjectContext   objectContext，DatabaseExistenceState existState）+150
  System.Data.Entity.Database.Create（DatabaseExistenceState   presenceState）+444
  System.Data.Entity.DropCreateDatabaseAlways 1.InitializeDatabase(TContext context) +158
System.Data.Entity.Internal.<>c__DisplayClassf 1.b__e（）   +165 System.Data.Entity.Internal.InternalContext.PerformInitializationAction（Action   行动）+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   行动）+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.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）+70
  System.Data.Entity.DbSet 1.FindAsync(Object[] keyValues) +69
Microsoft.AspNet.Identity.EntityFramework.EntityStore 1.GetByIdAsync（对象   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（）+ 123 Microsoft.AspNet.Identity.Owin。＆lt; b__1＆gt; 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（Task   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（Task   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（Task   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（Task   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（Task   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的   ar）+150
  Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.EndFinalWork（IAsyncResult的   ar）+42
  System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute（）   +380 System.Web.HttpApplication.ExecuteStep（IExecutionStep step，Boolean＆amp; completedSynchronously）+155

Answer 1

尝试在迁移中的Create语句之前移动DropTable语句。这样您就可以在创建新表之前删除现有的Employee表。