c# - EF 6.1 序列包含多个元素

Question

今天我将 EF 从 5 更新到了 6，我按照 MSDN 中的以下步骤进行操作:

http://msdn.microsoft.com/en-us/data/upgradeef6.aspx

现在的问题是，当我查询任何存储库时，如下所示:

mapEntitiesContext.ContextParameterScreens
                  .Where(p => p.OwningTenantId == IdentityHelper.IdPrv.TenantId)
                  .Select(p => new
                               {
                                   p.ParameterScreenDefinitionId,
                                   p.MedicalContextId
                               })
                  .FirstOrDefault();

我收到错误:

Sequence contains more then one element.

我在使用 EF 5.0 时从未遇到过此问题。

Stacktrace

    System.InvalidOperationException: Sequence contains more than one element

Result StackTrace:  

   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.<>c__DisplayClass281.<IndexesEqual>b__27e(String c)
   at System.Linq.Enumerable.<>c__DisplayClass12`3.<CombineSelectors>b__11(TSource x)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.SequenceEqual[TSource](IEnumerable`1 first, IEnumerable`1 second, IEqualityComparer`1 comparer)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.IndexesEqual(ConsolidatedIndex consolidatedIndex1, ConsolidatedIndex consolidatedIndex2, ICollection`1 renamedColumns)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.<>c__DisplayClass272.<FindAddedIndexes>b__26e(ConsolidatedIndex i1, ConsolidatedIndex i2)
   at System.Data.Entity.Utilities.DynamicEqualityComparer`1.Equals(T x, T y)
   at System.Linq.Set`1.Find(TElement value, Boolean add)
   at System.Linq.Set`1.Add(TElement value)
   at System.Linq.Enumerable.<ExceptIterator>d__99`1.MoveNext()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.Diff(ModelMetadata source, ModelMetadata target, Lazy`1 modificationCommandTreeGenerator, MigrationSqlGenerator migrationSqlGenerator, String sourceModelVersion, String targetModelVersion)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.Diff(XDocument sourceModel, XDocument targetModel, Lazy`1 modificationCommandTreeGenerator, MigrationSqlGenerator migrationSqlGenerator, String sourceModelVersion, String targetModelVersion)
   at System.Data.Entity.Internal.InternalContext.ModelMatches(VersionedModel model)
   at System.Data.Entity.Internal.ModelCompatibilityChecker.CompatibleWithModel(InternalContext internalContext, ModelHashCalculator modelHashCalculator, Boolean throwIfNoMetadata, DatabaseExistenceState existenceState)
   at System.Data.Entity.Internal.InternalContext.CompatibleWithModel(Boolean throwIfNoMetadata, DatabaseExistenceState existenceState)
   at System.Data.Entity.Database.CompatibleWithModel(Boolean throwIfNoMetadata, DatabaseExistenceState existenceState)
   at System.Data.Entity.CreateDatabaseIfNotExists`1.InitializeDatabase(TContext context)
   at System.Data.Entity.Internal.InternalContext.<>c__DisplayClassf`1.<CreateInitializationAction>b__e()
   at System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action)
   at System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization()
   at System.Data.Entity.Internal.LazyInternalContext.<InitializeDatabase>b__4(InternalContext c)
   at System.Data.Entity.Internal.RetryAction`1.PerformAction(TInput input)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeDatabaseAction(Action`1 action)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeDatabase()
   at System.Data.Entity.Internal.InternalContext.Initialize()
   at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType)
   at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize()
   at System.Data.Entity.Internal.Linq.InternalSet`1.get_InternalContext()
   at System.Data.Entity.Infrastructure.DbQuery`1.System.Linq.IQueryable.get_Provider()
   at System.Linq.Queryable.Where[TSource](IQueryable`1 source, Expression`1 predicate)

Answer 1

经过大量测试和调试，我终于找到了一个“解决方案”。

我从一个新项目开始，并从“add-migration InitialCreate -verbose”开始，在 EF 6.0 中，此方法创建一个名为“InitialSchema”的新文件。

当我开始当前的迁移时(一年多前)，初始文件被命名为:Initial.txt。 只需添加一个名为“InitialSchema”的空类即可修复我的错误。

public partial class InitialSchema : DbMigration
{
    public override void Up()
    {
    }

    public override void Down()
    {
    }
}

当我启动应用程序并创建 DbContext 时，EF 崩溃了

希望它也能帮助其他人:)