加载相关对象时例外。实体框架 [英] Exception when loading related objects. Entity Framework
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问题描述
我在我的数据库加载相关对象时，得到一个例外。我加载我所有的 MatchData 的对象，我想用一个foreach迭代他们。
I am getting an exception when loading related objects in my db. I am loading all my MatchData objects and I want to iterate them with a foreach.
这是我的目标M状加载是：
The objects that I'm loading is:
MatchData类：
MatchData Class:
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类：
PlayerData Class:
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; }
}
下面是我如何加载它们的MatchData对象：
Here is how I load them the MatchData objects:
using (DBBooneContext db = new DBBooneContext())
{
var smth = db.MatchData
.Include(md => md.BlueTeam)
.ToList();
}
的DbContext
DBContext
class DBBooneContext : DbContext
{
public DbSet<Player> Player { get; set; }
public DbSet<PlayerData> PlayerData { get; set; }
public DbSet<MatchData> MatchData { get; set; }
}
当我运行了ToList我得到异常：
的类型'System.Reflection.TargetInvocationException'的未处理的异常出现在EntityFramework.SqlServer.dll
When I run the ToList i get the exception: An unhandled exception of type 'System.Reflection.TargetInvocationException' occurred in EntityFramework.SqlServer.dll
全面例外：
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.
我绝对不知道如何解决这个问题。任何想法
I have absolutely no clue how to solve this issue. Any ideas?
推荐答案
内部异常说明了一切：
类Boonekamp.ClassCollection.PlayerData'没有参数的
构造
The class 'Boonekamp.ClassCollection.PlayerData' has no parameterless constructor
更改 PlayerData 来：
[Obsolete("Only needed for serialization and materialization", true)]
public PlayerData() {}
public PlayerData(Player player)
{
}
这样，你有一个无参数的构造函数，实体框架将能初始化过程中使用。然而，可以防止使用 [作废] 属性使用的代码，构造函数。
This way, you do have a parameter-less constructor that Entity Framework will be able to use during initialization. Yet, you prevent using that constructor in code using the [Obsolete] attribute.
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