Web API,OData,EF5,Union:'Distinct'操作不能应用于指定参数的集合ResultType

Question

我正在使用OData Nuget包处理Web API原型.我在使用LINQ to EF查询时遇到了一些问题.

这是我的数据模型.它已被高度简化.

我正在尝试使用此DTO使查询正常工作:

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public IEnumerable<Order> Orders { get; set; }
}

public class Order
{
    public int Id { get; set; }
    public DateTime Date { get; set; }
}

查询如下所示:

[Queryable]
public IQueryable<Product> Get()
{
    var productA = _context.ProductA
                            .Select(p => new Product
                                {
                                    Id = p.id,
                                    Name = p.name,
                                    Orders = p.ProductAOrders.Select(o => new Order
                                        {
                                            Id = o.OrderId,
                                            Date = o.Orders.Date,
                                        })
                                });

    var productB = _context.ProductB
                            .Select(p => new Product
                                {
                                    Id = p.Id,
                                    Name = p.Name,
                                    Orders = p.ProductBOrders.Select(o => new Order
                                        {
                                            Id = o.OrderId,
                                            Date = o.Orders.Date,
                                        })
                                });

    return productA.Union(productB);
}

尝试联合这两个查询时,我收到此错误:

<Error><Message>An error has occurred.</Message><ExceptionMessage>The 'Distinct' operation cannot be applied to the collection ResultType of the specified argument.
Parameter name: argument</ExceptionMessage><ExceptionType>System.ArgumentException</ExceptionType><StackTrace>   at System.Data.Common.CommandTrees.ExpressionBuilder.Internal.ArgumentValidation.ValidateDistinct(DbExpression argument)
   at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.UnionTranslator.TranslateBinary(ExpressionConverter parent, DbExpression left, DbExpression right)
   at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.BinarySequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
   at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)
   at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
   at System.Data.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Objects.ELinq.ExpressionConverter.Convert()
   at System.Data.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
   at System.Data.Objects.ObjectQuery.ToTraceString()
   at System.Data.Entity.Internal.Linq.InternalQuery`1.ToString()
   at System.Data.Entity.Infrastructure.DbQuery`1.ToString()
   at System.Convert.ToString(Object value, IFormatProvider provider)
   at System.Web.Http.Tracing.Tracers.HttpActionDescriptorTracer.&lt;ExecuteAsync&gt;b__2(TraceRecord tr, Object value)
   at System.Web.Http.Tracing.ITraceWriterExtensions.&lt;&gt;c__DisplayClass1b`1.&lt;&gt;c__DisplayClass1f.&lt;TraceBeginEndAsync&gt;b__13(TraceRecord traceRecord)
   at System.Web.Http.Tracing.SystemDiagnosticsTraceWriter.Trace(HttpRequestMessage request, String category, TraceLevel level, Action`1 traceAction)
   at System.Web.Http.Tracing.ITraceWriterExtensions.&lt;&gt;c__DisplayClass1b`1.&lt;TraceBeginEndAsync&gt;b__12(TResult result)
   at System.Threading.Tasks.TaskHelpersExtensions.&lt;&gt;c__DisplayClass3b`2.&lt;Then&gt;b__3a(Task`1 t)
   at System.Threading.Tasks.TaskHelpersExtensions.ThenImpl[TTask,TOuterResult](TTask task, Func`2 continuation, CancellationToken cancellationToken, Boolean runSynchronously)
</StackTrace></Error>

我可以返回productA或productB - 但返回这两个查询的Union会导致上面的明显错误.

对我可能做错的任何想法？

Answer 1

看起来像一个EF错误.我假设您正在尝试使MEST(同一类型的多个实体集)正常工作.您可以尝试,而不是您拥有的查询,

public IQueryable<Product> Get()
{
    var productA = _context.ProductA
                            .Select(p => new Product
                            {
                                Id = p.id,
                                Name = p.name,
                            });

    var productB = _context.ProductB
                            .Select(p => new Product
                            {
                                Id = p.Id,
                                Name = p.Name,
                            });

    return
        productA
        .Union(productB)
        .Select(p => new Product
        {
            Id = p.Id,
            Name = p.Name,
            Orders = _context.Orders
                    .Where(o => o.ProductA.Id == p.Id || o.ProductB.Id == p.Id)
                    .Select(o => new Order
                    {
                        Id = o.OrderId,
                        Date = o.Orders.Date,
                    })
        });
}

我们的想法是将导航属性从联合中取出并稍后再添加它们.只有当Orders返回指向ProductA或ProductB的指针时,这才有效.