加載相關對象時出現異常。 實體框架

Question

我在db中加載相關對象時遇到異常。 我正在加載我的所有MatchData對象，我想用foreach迭代它們。

我正在加載的對象是：

MatchData類：

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; }
    }
}

PlayerData類：

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; }
}

以下是我如何加載MatchData對象：

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

的DbContext

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

當我運行ToList時，我得到異常：EntityFramework.SqlServer.dll中發生了未處理的異常類型'System.Reflection.TargetInvocationException'

完全例外：

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決這個問題。 有任何想法嗎？

Answer 1

內在的例外說明了一切：

類'Boonekamp.ClassCollection.PlayerData'沒有無參數構造函數

將您的PlayerData更改為：

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

public PlayerData(Player player)
{
}

這樣，您就可以使用Entity Framework在初始化期間可以使用的無參數構造函數。 但是，您使用[Obsolete]屬性阻止在代碼中使用該構造函數。