不支持嵌套查询.Operation1 ='UnionAll'Operation2 ='MultiStreamNest'

Question

我有以下形式的Linq to Entities查询:

var x = from a in SomeData
    where ... some conditions ...
    select new MyType
    {
        Property = a.Property,
        ChildCollection = from b in a.Children
                        select new MyChildType
                        {
                            SomeProperty = b.Property,
                            AnotherProperty = b.AnotherProperty
                        }
    };

var y = from a in SomeData
    where ... some other conditions ...
    select new MyType
    {
        Property = a.Property,
        ChildCollection = from b in a.Children
                        select new MyChildType
                        {
                            SomeProperty = b.Property,
                            AnotherProperty = b.AnotherProperty
                        }
    };

var results = x.Concat(y);

(这是一个简化的例子 - 'where'和'select'子句比这里显示的更复杂.我使用单独的查询语句,因为创建单个组合的语句太复杂,有太多的条件并需要一个年龄编译)

编译正常,但在执行时失败,异常:

"The nested query is not supported. Operation1='UnionAll' Operation2='MultiStreamNest'

注意,我试图投射到嵌套的类型结构.如果我在Concat()之前在x和y上调用.ToList()它可以正常工作.另外一点,我的一个属性是枚举,但是我使用整数包装器属性来分配它.

有没有办法我可以做我想做的事情,而不必将所有数据都拉入内存？或者是导致失败的枚举？

谢谢,

Ť

Answer 1

你有没有尝试过

 var results = x.Union(y);

？

提兹

或者

var x = (from a in SomeData
where ... some conditions ...
select new MyType
{
    Property = a.Property,
    ChildCollection = (from b in a.Children
                    select new MyChildType
                    {
                        SomeProperty = b.Property,
                        AnotherProperty = b.AnotherProperty
                    }).ToArray() //or DefaultIfEmpty
}).Concat(
from a in SomeData
where ... some other conditions ...
select new MyType
{
    Property = a.Property,
    ChildCollection = (from b in a.Children
                    select new MyChildType
                    {
                        SomeProperty = b.Property,
                        AnotherProperty = b.AnotherProperty
                    }).ToArray() //or DefaultIfEmpty
});