c# - 加载相关对象时出现异常。 Entity Framework

Question

在我的数据库中加载相关对象时出现异常。我正在加载我所有的 MatchData 对象，我想用 foreach 迭代它们。

我正在加载的对象是:

匹配数据类:

public class MatchData
{
    [Key]
    public virtual int Id { get; set; }
    private List<PlayerData> blueTeam = new List<PlayerData>();
    private List<PlayerData> redTeam = new List<PlayerData>();

    [InverseProperty("MatchDataBlue")]
    public virtual List<PlayerData> BlueTeam
    {
        get { return blueTeam; }
        set { blueTeam = value; }
    }
    [InverseProperty("MatchDataRed")]
    public virtual List<PlayerData> RedTeam
    {
        get { return redTeam; }
        set { redTeam = value; }
    }
}

玩家数据类:

public class PlayerData
{

    // properties
    [Key]
    public virtual int Id { get; set; }

    public virtual Player Player { get; set; }
    public virtual MatchData MatchDataBlue { get; set; }
    public virtual MatchData MatchDataRed { get; set; }
}

下面是我如何加载 MatchData 对象:

using (DBBooneContext db = new DBBooneContext())
{
    var smth = db.MatchData
        .Include(md => md.BlueTeam)
        .ToList();
}

数据库上下文

class DBBooneContext : DbContext
{
    public DbSet<Player> Player { get; set; }
    public DbSet<PlayerData> PlayerData { get; set; }
    public DbSet<MatchData> MatchData { get; set; }
}

当我运行 ToList 时，出现异常: EntityFramework.SqlServer.dll 中出现“System.Reflection.TargetInvocationException”类型的未处理异常

完全异常(exception):

A first chance exception of type 'System.Reflection.TargetInvocationException' occurred in EntityFramework.SqlServer.dll
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: The class 'Boonekamp.ClassCollection.PlayerData' has no parameterless constructor.
   at System.Data.Entity.Core.Objects.DelegateFactory.GetConstructorForType(Type type)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Emit_ConstructEntity(EntityType oSpaceType, IEnumerable`1 propertyBindings, Expression entityKeyReader, Expression entitySetReader, TranslatorArg arg, EntityProxyTypeInfo proxyTypeInfo)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(EntityColumnMap columnMap, TranslatorArg arg)
   at System.Data.Entity.Core.Query.InternalTrees.EntityColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.HandleSpandexRecord(RecordColumnMap columnMap, TranslatorArg arg, RowType spanRowType)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(RecordColumnMap columnMap, TranslatorArg arg)
   at System.Data.Entity.Core.Query.InternalTrees.RecordColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.ProcessCollectionColumnMap(CollectionColumnMap columnMap, TranslatorArg arg, ColumnMap discriminatorColumnMap, Object discriminatorValue)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(DiscriminatedCollectionColumnMap columnMap, TranslatorArg arg)
   at System.Data.Entity.Core.Query.InternalTrees.DiscriminatedCollectionColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.AcceptWithMappedType(TranslatorVisitor translatorVisitor, ColumnMap columnMap)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.HandleSpandexRecord(RecordColumnMap columnMap, TranslatorArg arg, RowType spanRowType)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(RecordColumnMap columnMap, TranslatorArg arg)
   at System.Data.Entity.Core.Query.InternalTrees.RecordColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.ProcessCollectionColumnMap(CollectionColumnMap columnMap, TranslatorArg arg, ColumnMap discriminatorColumnMap, Object discriminatorValue)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.ProcessCollectionColumnMap(CollectionColumnMap columnMap, TranslatorArg arg)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(SimpleCollectionColumnMap columnMap, TranslatorArg arg)
   at System.Data.Entity.Core.Query.InternalTrees.SimpleCollectionColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslateColumnMap[T](ColumnMap columnMap, MetadataWorkspace workspace, SpanIndex spanIndex, MergeOption mergeOption, Boolean streaming, Boolean valueLayer)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
   at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslateColumnMap(Translator translator, Type elementType, ColumnMap columnMap, MetadataWorkspace workspace, SpanIndex spanIndex, MergeOption mergeOption, Boolean streaming, Boolean valueLayer)
   at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.Prepare(ObjectContext context, DbQueryCommandTree tree, Type elementType, MergeOption mergeOption, Boolean streaming, Span span, IEnumerable`1 compiledQueryParameters, AliasGenerator aliasGenerator)
   at System.Data.Entity.Core.Objects.EntitySqlQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Boonekamp.ClassCollection.Player.getStats(Predicate`1 predicate) in d:\Dropbox\code\c#\Boonekamp\Boonekamp\ClassCollection\Player.cs:line 49

Additional information: Exception has been thrown by the target of an invocation.

我完全不知道如何解决这个问题。有什么想法吗？

Answer 1

内部异常说明了一切:

The class 'Boonekamp.ClassCollection.PlayerData' has no parameterless constructor

将您的 PlayerData 更改为:

[Obsolete("Only needed for serialization and materialization", true)]
public PlayerData() {}

public PlayerData(Player player)
{
}

这样，您就有了 Entity Framework 可以在初始化期间使用的无参数构造函数。然而，您可以使用 [Obsolete] 属性阻止在代码中使用该构造函数。