ASP.NETSequence包含多个元素

Question

我有3个非常简单的类一个类别，一个是产品，一个用于图像 迁移后并尝试更新数据库，但和过程结束时，我得到一个

Sequence contains more than one element 

整件事情在下面，但请注意它说的是关于配置类的第73行的内容。 这里是包含在年底这个类的一个片段，该行

var imagenes = new List<Image> 
      { 
       new Image{ ID = 1, ImageName = "Horizontal_Faux_Wood", ImagePath="Content/ProductImages/fauxwoodblinds1.jpg", ProductID = 1}, 
       new Image{ ID = 2, ImageName = "Horizontal_Real_Wood", ImagePath="Content/ProductImages/woodblinds1.jpg", ProductID = 2}, 
       new Image{ ID = 3, ImageName = "Roller_Shade_Screens", ImagePath="Content/ProductImages/product-rollupshades-a-5p.jpg", ProductID = 3}, 
       new Image{ ID = 4, ImageName = "BlackOut", ImagePath="Content/ProductImages/product-rollupshades-9-blackout_soft_side channel.jpg", ProductID = 4}, 
       new Image{ ID = 5, ImageName = "Vertical_Faux_Wood", ImagePath="Content/ProductImages/verticalfauxwood.jpg", ProductID = 5}, 
       new Image{ ID = 6, ImageName = "Vertical_PVC_Textured", ImagePath="Content/ProductImages/woodblindspeq.jpg", ProductID = 6}, 
       new Image{ ID = 7, ImageName = "Vertical_PVC_Plain", ImagePath="Content/ProductImages/vertical.jpg", ProductID = 7}, 

      }; 


(line 73)  imagenes.ForEach(m => context.Images.AddOrUpdate(x => x.ImagePath, m)); context.SaveChanges(); 

而且herewhat显示后，我尝试更新数据库

PM> update-database 
Specify the '-Verbose' flag to view the SQL statements being applied to the target database. 
No pending explicit migrations. 
Running Seed method. 
System.InvalidOperationException: Sequence contains more than one element 
    at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source) 
    at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>b__2[TResult](IEnumerable`1 sequence) 
    at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.ExecuteSingle[TResult](IEnumerable`1 query, Expression queryRoot) 
    at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[TResult](Expression expression) 
    at System.Data.Entity.Internal.Linq.DbQueryProvider.Execute[TResult](Expression expression) 
    at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source, Expression`1 predicate) 
    at System.Data.Entity.Migrations.DbSetMigrationsExtensions.AddOrUpdate[TEntity](DbSet`1 set, IEnumerable`1 identifyingProperties, InternalSet`1 internalSet, TEntity[] entities) 
    at System.Data.Entity.Migrations.DbSetMigrationsExtensions.AddOrUpdate[TEntity](IDbSet`1 set, Expression`1 identifierExpression, TEntity[] entities) 
    at AllBlindsNewWeb.Migrations.Configuration.<>c__DisplayClass1_0.<Seed>b__2(Image m) in C:\Users\Ernesto\Documents\Visual Studio 2015\Projects\training\AllBlindsNewWeb\AllBlindsNewWeb\Migrations\Configuration.cs:line 73 
    at System.Collections.Generic.List`1.ForEach(Action`1 action) 
    at AllBlindsNewWeb.Migrations.Configuration.Seed(ProductContext context) in C:\Users\Ernesto\Documents\Visual Studio 2015\Projects\training\AllBlindsNewWeb\AllBlindsNewWeb\Migrations\Configuration.cs:line 73 
    at System.Data.Entity.Migrations.DbMigrationsConfiguration`1.OnSeed(DbContext context) 
    at System.Data.Entity.Migrations.DbMigrator.SeedDatabase() 
    at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.SeedDatabase() 
    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) 
Sequence contains more than one element 

我不能看到/明白的地方/什么错误 谢谢

Answer 1

您正在使用AddOrUpdate获取重复项。似乎应该使用ID作为唯一密钥：

imagenes.ForEach(m => context.Images.AddOrUpdate(x => x.ID, m)); 
context.SaveChanges(); 

此外，请确保清除Images表中的任何冲突记录。

http://thedatafarm.com/data-access/take-care-with-ef-4-3-addorupdate-method/