在MVC Web Api中使用EntitySetController扩展集合

Question

我正在使用OData框架（版本5.0.0）和MVC Web Api（MVC版本4.0.305060），无法让$expand查询为我的集合工作。

根据这个wiki页面，更具体地说，在"支持的场景"下的案例#2，我应该能够扩展集合，将其数据包含在一个查询中，但我的$expand查询似乎被完全忽略了。没有错误，响应完全相同，就像我完全忽略了$expand一样。

这是我的数据结构的一部分：

DebtCalculation
    - string Name
    - string Description
    - Collection<Expense> Expenses
    - Collection<Participant> Participants
Participant
    - bool HasPaid
    - User User
    - DebtCalculation DebtCalculation
Expense
    - decimal Amount
    - User Payer
    - Collection<Debtor> Debtors
    - DebtCalculation DebtCalculation

总结；通过myservice/api/Expenses?$expand=Payer和myservice/api/Expenses(10)?$expand=Payer，使用$expand查询单个实体可以正常工作，但查询myservice/api/DebtCalculations?$expand=Participants则不然。

这是我的控制器和ODataConventionModelBuilder设置的一部分：

[Authorize]
public class DebtCalculationsController : EntitySetController<DebtCalculation, long>
{
    private DebtCalculationManager _debtCalculationManager { get; set; }
    public DebtCalculationsController(DebtCalculationManager debtCalculationManager)
    {
        _debtCalculationManager = debtCalculationManager;
    }
    public override IQueryable<DebtCalculation> Get()
    {
        return _debtCalculationManager.AllDebtCalculationsForApi();
    }
    protected override DebtCalculation GetEntityByKey(long key)
    {
        return _debtCalculationManager.GetDebtCalculation(key);
    }
    public IQueryable<Participant> GetParticipants(long key)
    {
        return _debtCalculationManager.GetDebtCalculation(key).Participants.AsQueryable();
    }
    public IQueryable<Expense> GetExpenses(long key)
    {
        return _debtCalculationManager.GetDebtCalculation(key).Expenses.AsQueryable();
    }
}
[Authorize]
public class ExpensesController : EntitySetController<Expense, long>
{
    private DebtCalculationManager _debtCalculationManager { get; set; }
    public ExpensesController(DebtCalculationManager debtCalculationManager)
    {
        _debtCalculationManager = debtCalculationManager;
    }
    public override IQueryable<Expense> Get()
    {
        return _debtCalculationManager.AllDebtCalculationsForApi()
            .SelectMany(dc => dc.Expenses);
    }
    protected override Expense GetEntityByKey(long key)
    {
        return _debtCalculationManager.ExpenseForApi(key);
    }
    public User GetPayer(long key)
    {
        return _debtCalculationManager.ExpenseForApi(key).Payer;
    }
    public IQueryable<Debtor> GetDebtors(long key)
    {
        return _debtCalculationManager.ExpenseForApi(key).Debtors.AsQueryable();
    }
    public DebtCalculation GetDebtCalculation(long key)
    {
        return _debtCalculationManager.ExpenseForApi(key).DebtCalculation;
    }
}
[Authorize]
public class ParticipantsController : EntitySetController<Participant, long>
{
    private DebtCalculationManager _debtCalculationManager { get; set; }
    public ParticipantsController(DebtCalculationManager debtCalculationManager)
    {
        _debtCalculationManager = debtCalculationManager;
    }
    public override IQueryable<Participant> Get()
    {
        return _debtCalculationManager.AllDebtCalculationsForApi()
            .SelectMany(dc => dc.Participants);
    }
    protected override Participant GetEntityByKey(long key)
    {
        return _debtCalculationManager.ParticipantForApi(key);
    }
    public DebtCalculation GetDebtCalculation(long key)
    {
        return _debtCalculationManager.ParticipantForApi(key).DebtCalculation;
    }
}
public static class WebApiConfig
{
    public static HttpConfiguration Config { get; set; }
    public static void Register(HttpConfiguration config)
    {
        var modelBuilder = new ODataConventionModelBuilder();
        modelBuilder.EntitySet<DebtCalculation>("DebtCalculations")
            .EntityType.HasKey(dc => dc.Id);
        modelBuilder.EntitySet<Participant>("Participants")
            .EntityType.HasKey(p => p.Id)
            .Ignore(p => p.UniqueKey);
        modelBuilder.EntitySet<Expense>("Expenses")
            .EntityType.HasKey(e => e.Id);
        ...
        var model = modelBuilder.GetEdmModel();
        var routingConventions = ODataRoutingConventions.CreateDefault();
        routingConventions.Insert(0, new CreateNavigationPropertyRoutingConvention());
        config.Routes.MapODataRoute("ODataRoute", "api", model, new DefaultODataPathHandler(), routingConventions);
        config.EnableQuerySupport();
    }
    // routing convention to handle POST requests to navigation properties.
    public class CreateNavigationPropertyRoutingConvention : EntitySetRoutingConvention
    {
        public override string SelectAction(ODataPath odataPath, HttpControllerContext controllerContext, ILookup<string, HttpActionDescriptor> actionMap)
        {
            if (odataPath.PathTemplate == "~/entityset/key/navigation" && controllerContext.Request.Method == HttpMethod.Post)
            {
                IEdmNavigationProperty navigationProperty = (odataPath.Segments[2] as NavigationPathSegment).NavigationProperty;
                controllerContext.RouteData.Values["key"] = (odataPath.Segments[1] as KeyValuePathSegment).Value; // set the key for model binding.
                return "PostTo" + navigationProperty.Name;
            }
            return null;
        }
    }

DebtCalculation的元数据如下所示：

    <EntityType Name="DebtCalculation">
            <Key>
                    <PropertyRef Name="Id"/>
            </Key>
            <Property Name="Id" Type="Edm.Int64" Nullable="false"/>
            <Property Name="Name" Type="Edm.String"/>
            <Property Name="Description" Type="Edm.String"/>
            <NavigationProperty Name="Participants" Relationship="Sujut.Core.Sujut_Core_DebtCalculation_Participants_Sujut_Core_Participant_ParticipantsPartner" ToRole="Participants" FromRole="ParticipantsPartner"/>
            <NavigationProperty Name="Expenses" Relationship="Sujut.Core.Sujut_Core_DebtCalculation_Expenses_Sujut_Core_Expense_ExpensesPartner" ToRole="Expenses" FromRole="ExpensesPartner"/>
    </EntityType>

是否发现任何问题？

编辑：

问题似乎是将ODataController查询与Linq结合到NHibernate。这是堆栈跟踪。升级到NH 4.0.0.1000 alpha版本并没有解决这个问题。这个错误报告似乎是关于同一个问题。

System.ArgumentException
at System.Linq.Expressions.Expression.Condition(Expression test, Expression ifTrue, Expression ifFalse)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitConditionalExpression(ConditionalExpression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.NestedSelects.SelectClauseRewriter.VisitExpression(Expression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitBinaryExpression(BinaryExpression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.NestedSelects.SelectClauseRewriter.VisitExpression(Expression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitConditionalExpression(ConditionalExpression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.NestedSelects.SelectClauseRewriter.VisitExpression(Expression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberAssignment(MemberAssignment memberAssigment)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberBinding(MemberBinding memberBinding)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitList[T](ReadOnlyCollection`1 list, Func`2 visitMethod)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberBindingList(ReadOnlyCollection`1 expressions)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberInitExpression(MemberInitExpression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.NestedSelects.SelectClauseRewriter.VisitExpression(Expression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberAssignment(MemberAssignment memberAssigment)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberBinding(MemberBinding memberBinding)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitList[T](ReadOnlyCollection`1 list, Func`2 visitMethod)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberBindingList(ReadOnlyCollection`1 expressions)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMemberInitExpression(MemberInitExpression expression)
 at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression)
 at NHibernate.Linq.NestedSelects.SelectClauseRewriter.VisitExpression(Expression expression)
 at NHibernate.Linq.NestedSelects.NestedSelectRewriter.ReWrite(QueryModel queryModel, ISessionFactory sessionFactory)
 at NHibernate.Linq.Visitors.QueryModelVisitor.GenerateHqlQuery(QueryModel queryModel, VisitorParameters parameters, Boolean root)
 at NHibernate.Linq.NhLinqExpression.Translate(ISessionFactoryImplementor sessionFactory)
 at NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(String queryIdentifier, IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 filters, ISessionFactoryImplementor factory)
 at NHibernate.Engine.Query.HQLExpressionQueryPlan.CreateTranslators(String expressionStr, IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 enabledFilters, ISessionFactoryImplementor factory)
 at NHibernate.Engine.Query.HQLExpressionQueryPlan..ctor(String expressionStr, IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 enabledFilters, ISessionFactoryImplementor factory)
 at NHibernate.Engine.Query.HQLExpressionQueryPlan..ctor(String expressionStr, IQueryExpression queryExpression, Boolean shallow, IDictionary`2 enabledFilters, ISessionFactoryImplementor factory)
 at NHibernate.Engine.Query.QueryPlanCache.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow, IDictionary`2 enabledFilters)
 at NHibernate.Impl.AbstractSessionImpl.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow)
 at NHibernate.Impl.AbstractSessionImpl.CreateQuery(IQueryExpression queryExpression)
 at NHibernate.Linq.DefaultQueryProvider.PrepareQuery(Expression expression, IQuery& query, NhLinqExpression& nhQuery)
 at NHibernate.Linq.DefaultQueryProvider.Execute(Expression expression)
 at NHibernate.Linq.DefaultQueryProvider.Execute[TResult](Expression expression)
 at Remotion.Linq.QueryableBase`1.System.Collections.IEnumerable.GetEnumerator()
 at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteFeed(IEnumerable enumerable, IEdmTypeReference feedType, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteObjectInline(Object graph, IEdmTypeReference expectedType, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteObject(Object graph, Type type, ODataMessageWriter messageWriter, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.ODataMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content, HttpContentHeaders contentHeaders)
 at System.Web.Http.OData.Formatter.ODataMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext)
 --- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__14.MoveNext()

Answer 1

问题是Linq到NHibernate，这里报告了错误。

通过对返回的IQueryable<DebtCalculation>集调用.ToList().AsQueryable()来解决此问题。这显然不是很有效，但将允许我继续开发和测试依赖API的应用程序，直到修复错误。

Answer 2

我遇到了同样的问题，并尝试了解决方法，但对于大型数据集，由于延迟加载，它似乎会触发很多select语句。

因此，我采取了一种不同的方法，手动连接相关的表。

  // Using Chinook Database
  Album albumAlias = null;
  Track trackAlias = null;
  Artist artistAlias = null;
  return session.QueryOver<Album>(() => albumAlias)
    .Left.JoinAlias(() => albumAlias.Tracks, () => trackAlias)
    .Left.JoinAlias(() => albumAlias.Artist, () => artistAlias)
    .TransformUsing(Transformers.DistinctRootEntity)
    .List().AsQueryable();

专辑有许多曲目和一个与之相关的艺术家。通过这种方式，它将只生成一个select语句，并且仍然能够扩展任一属性。

例如，它可能看起来像

DebtCalculation debtCalculationAlias = null;
Expense expenseAlias = null;
Participant participantAlias = null;
session.QueryOver<DebtCalculation>(() => debtCalculationAlias)
.Left.JoinAlias(() => debtCalculationAlias.Expenses, () => expenseAlias)
.Left.JoinAlias(() => debtCalculationAlias.Participants, () => participantAlias)
.TransformUsing(Transformers.DistinctRootEntity)
.List().AsQueryable();

我刚刚进入OData，所以如果你认为这不是正确的方法，请随时纠正我。