Question

我已经看到大多数人在使用SingleOrDefault时都会收到此错误。但是，我正在使用FirstOrDefault。以前有人见过这种异常吗？我正在使用存储库模式以使用依赖注入。

return context.Users.FirstOrDefault(p => p.Username.ToLower() == username.ToLower());

修改

见下文：错误来自EntityFramework的内部代码。我可以告诉你。

[InvalidOperationException: Sequence contains more than one matching element]
   System.Linq.Enumerable.SingleOrDefault(IEnumerable`1 source, Func`2 predicate) +2668318
   System.Data.Entity.ModelConfiguration.Conventions.IdKeyDiscoveryConventionImpl.MatchKeyProperty(EdmEntityType entityType, IEnumerable`1 primitiveProperties) +121
   System.Data.Entity.ModelConfiguration.Conventions.KeyDiscoveryConvention.System.Data.Entity.ModelConfiguration.Conventions.IEdmConvention<System.Data.Edm.EdmEntityType>.Apply(EdmEntityType entityType, EdmModel model) +72
   System.Data.Entity.ModelConfiguration.Conventions.IdKeyDiscoveryConvention.System.Data.Entity.ModelConfiguration.Conventions.IEdmConvention<System.Data.Edm.EdmEntityType>.Apply(EdmEntityType entityType, EdmModel model) +17
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.Dispatch(TEdmDataModelItem item) +100
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.VisitEdmEntityType(EdmEntityType item) +22
   System.Data.Edm.Internal.DataModelItemVisitor.VisitCollection(IEnumerable`1 collection, Action`1 visitMethod) +138
   System.Data.Edm.Internal.EdmModelVisitor.VisitEntityTypes(EdmNamespace edmNamespace, IEnumerable`1 entityTypes) +75
   System.Data.Edm.Internal.EdmModelVisitor.VisitEdmNamespace(EdmNamespace item) +88
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.VisitEdmNamespace(EdmNamespace item) +31
   System.Data.Edm.Internal.DataModelItemVisitor.VisitCollection(IEnumerable`1 collection, Action`1 visitMethod) +138
   System.Data.Edm.Internal.EdmModelVisitor.VisitNamespaces(EdmModel model, IEnumerable`1 namespaces) +75
   System.Data.Edm.Internal.EdmModelVisitor.VisitEdmModel(EdmModel item) +56
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.VisitEdmModel(EdmModel item) +44
   System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ApplyModel(EdmModel model) +126
   System.Data.Entity.DbModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo) +125
   System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection) +165
   System.Data.Entity.Internal.LazyInternalContext.CreateModel(LazyInternalContext internalContext) +61
   System.Data.Entity.Internal.RetryLazy`2.GetValue(TInput input) +111
   System.Data.Entity.Internal.LazyInternalContext.InitializeContext() +417
   System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType) +18
   System.Data.Entity.Internal.Linq.InternalSet`1.Initialize() +63
   System.Data.Entity.Internal.Linq.InternalSet`1.get_InternalContext() +15
   System.Data.Entity.Infrastructure.DbQuery`1.System.Linq.IQueryable.get_Provider() +37
   System.Linq.Queryable.FirstOrDefault(IQueryable`1 source, Expression`1 predicate) +63
   Entities.User.GetCurrentPerson(String username, KmManagerDbContext context) in C:\Users\user\Documents\Visual Studio 2010\Projects\KmManager\Entities\User.cs:85

User.cs

public class User
{
    public long Id { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string Username { get; set; }

    // Custom Propreties
    public string FullName
    {
        get
        {
            return FirstName + " " + LastName;
        }
    }

    public string LastNameFirst
    {
        get
        {
            return LastName + ", " + FirstName;
        }
    }

    public static string TableName
    {
        get
        {
            return "Users";
        }
    }

    public static User GetCurrentPerson(string username, KmManagerDbContext context)
    {
        try
        {
            // find the person who has the ad name = username
            return context.Users.FirstOrDefault(p => p.Username.ToLower() == username.ToLower());
        }
        catch (Exception ex)
        {
            throw new ApplicationException("There was an error retrieving the user from the database.", ex);
        }
    }
}

UserConfiguration.cs

public UserConfiguration()
{
    this.ToTable(User.TableName);

    this.HasKey(x => x.Id);

    this.Property(x => x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
    this.Property(x => x.FirstName).IsRequired();
    this.Property(x => x.LastName).IsRequired();
    this.Property(x => x.Username).IsRequired();
}

Answer 1

如果有人担心答案......

我使用BaseEntity.cs

在我的POCO中分离了一些共性

BaseEntity.cs

public class BaseEntity<T> where T : BaseEntity<T>
{
    public long Id { get; set; }

    public class Comparer : IEqualityComparer<T>
    {
        public bool Equals(T x, T y)
        {
            if (x.Id == y.Id)
            {
                return true;
            }

            return false;
        }

        public int GetHashCode(T obj)
        {
            return (int)obj.Id;
        }
    }
}

这导致配置具有奇怪的行为。我将所有POCO更改为之前的状态，一切都按预期工作。抱歉浪费时间。

用户POCO看起来像这样......

User.cs

public class User : BaseEntity<User>
{
    public string FirstName { get; set; } 

    public string LastName { get; set; } 

    public string Username { get; set; } 

    // Custom Propreties 
    public string FullName 
    { 
        get 
        { 
            return FirstName + " " + LastName; 
        } 
    } 

    public string LastNameFirst 
    { 
        get 
        { 
            return LastName + ", " + FirstName; 
        } 
    } 

    public static string TableName 
    { 
        get 
        { 
            return "Users"; 
        } 
    } 

    public static User GetCurrentPerson(string username, KmManagerDbContext context) 
    { 
        try 
        { 
            // find the person who has the ad name = username 
            return context.Users.FirstOrDefault(p => p.Username.ToLower() == username.ToLower()); 
        } 
        catch (Exception ex) 
        { 
            throw new ApplicationException("There was an error retrieving the user from the database.", ex); 
        } 
    } 
}

Answer 2

此错误不是查询问题，而是映射配置问题。似乎无论您在调用EF代码的查询是否会在类上找到重复的匹配属性时抛出错误。我猜它是在类公共setter中通过PropertyInfos循环。可能有重复的属性名称因为c＃区分大小写所以'MyProperty'，'myproperty'都映射到同一列，或者在我的情况下因为自定义类索引器

对于类索引器： .net框架将索引器反映为properties with parameters。目前无法忽略EntityFramework代码第一个映射文件中的自定义索引器，因为lambda表达式无法表达这些特殊属性。由于这还不够，我的类有一个重载索引器（因此错误'序列包含多个匹配元素'）

示例：

public decimal this[int month] {
    get {
        return _someArray[month];
    }
    set {
        _someArray[month] = value;
    }
}

public decimal this[int front, int month] {
    get {
        return _someArray2D[front - 1, month - 1];
    }
    set {
        _someArray2D[front - 1, month - 1] = value;
    }
}

很难跟踪。花了我一整天的时间来试图通过反复试验。

希望这有助于某人。

Answer 3

不是答案，而是一个提示。基于Tekerik JustDecompile，该方法看起来像（EntityFramework.dll v4.2.0.0）：

protected override EdmProperty MatchKeyProperty(EdmEntityType entityType, IEnumerable<EdmProperty> primitiveProperties)
{
    return primitiveProperties.SingleOrDefault<EdmProperty>(delegate {
        return string.Concat(entityType.Name, "Id").Equals(p.Name, stringComparison);
    }) ?? primitiveProperties.SingleOrDefault<EdmProperty>(delegate {
        return string.Concat(entityType.Name, "Id").Equals(p.Name, stringComparison);
    });
}

似乎此函数试图找到您实体上的哪个属性是关键属性。期待用户 - ＆gt; UserId映射。我无法解释为什么SingleOrDefault被调用两次。

FirstOrDefault抛出'Sequence包含多个匹配元素'

修改

3 个答案: