QueryOver - 我以为 ID 是免费的？

Question

我花了一段时间，但我想出了如何得到我想要的东西——主要是。 我的代码：

        var sq = QueryOver.Of<VehicleGroup>(() => vehicleGroup)
                    .JoinQueryOver<Manager>(vg => vg.Managers)
                        .Where(man => man.Id == managerId)
                    .JoinQueryOver<TruckPCBase>(() => vehicleGroup.Vehicles)
                        .Where(v => v.Id == item.VehicleId)
                    .Select(vg => vg.Id)
                    ;

        var vp = Session.QueryOver<Summary>(() => item)
            .WithSubquery.WhereExists(sq)
            .Take(10)
            .List();

这正是我想要的。

但是，我必须映射一个附加字段才能使其正常工作。

Summary 对象有一个 VehicleBase 组件。我想做的是：

        var sq = QueryOver.Of<VehicleGroup>(() => vehicleGroup)
                    .JoinQueryOver<Manager>(vg => vg.Managers)
                        .Where(man => man.Id == managerId)
                    .JoinQueryOver<TruckPCBase>(() => vehicleGroup.Vehicles)
                        .Where(v => v.Id == item.VehicleBase.Id)
                    .Select(vg => vg.Id)
                    ;

        var vp = Session.QueryOver<Summary>(() => item)
            .WithSubquery.WhereExists(sq)
            .Take(10)
            .List();

这给出了以下错误：

System.NullReferenceException: Object reference not set to an instance of an object.
at lambda_method(ExecutionScope ) 

好的，所以我添加了一个额外的获取：

        var sq = QueryOver.Of<VehicleGroup>(() => vehicleGroup)
                    .JoinQueryOver<Manager>(vg => vg.Managers)
                        .Where(man => man.Id == managerId)
                    .JoinQueryOver<TruckPCBase>(() => vehicleGroup.Vehicles)
                        .Where(v => v.Id == item.VehicleBase.Id)
                    .Select(vg => vg.Id)
                    ;

        var vp = Session.QueryOver<Summary>(() => item)
            .Fetch(sum => sum.VehicleBase).Eager
            .WithSubquery.WhereExists(sq)
            .Take(10)
            .List();

没有骰子。我不想向我的 Summary 类 (VehicleId) 添加新属性 - 我想通过 Summary.VehicleBase.Id 访问它

？

Answer 1

我无法完全理解您正在尝试执行的操作，但问题似乎是：

您收到此异常是因为此行

.Where(v => v.Id == item.VehicleBase.Id)

item 为空。
nhibernate 的 linq 表达式求值器将尝试急切地求值不包含 lambda 参数的所有内容。对于这种情况：

v.Id => 将稍后进行评估并转向 HQL
item.VehicleBase.Id => 不依赖于 v，因此评估器会急切地评估它，这将引发 NRE。

Answer 2

得到它的工作！

var sq = QueryOver.Of<VehicleGroup>()
    .Inner.JoinAlias(vg => vg.Managers, () => manager)
    .Where(() => manager.Id == managerId)
    .JoinQueryOver(x => x.Vehicles, () => vehicle)
    .Select(x => vehicle.Id)
    ;


var vp = Session.QueryOver<Summary>()
    .Fetch(vpr => vpr.VehicleBase).Eager
    .WithSubquery.WhereProperty(x => x.VehicleBase.Id).In(sq)
    .Take(10)
    .List()
    ;

这会生成以下 SQL

SELECT
    TOP (@p0) this_.summaryID as summaryID42_1_,
    ... close to 200 columns cut ...
FROM
    dbo.Summary this_ 
left outer join
    dbo.Vehicle vehiclebas2_ 
        on this_.VehicleID = vehiclepcbas2_.VehicleID 
WHERE
    this_.vehicleID in (
        SELECT
            vehicle2_.vehicleID as y0_ 
        FROM
            dbo.Groups this_0_ 
        inner join
            dbo.Manager_Rel managers4_ 
                on this_0_.groupId=managers4_.groupId 
        inner join
            dbo.Managers manager1_ 
                on managers4_.managerId=manager1_.ManagerId 
        inner join
            dbo.Object_Rel vehicles6_ 
                on this_0_.groupId=vehicles6_.groupId 
        inner join
            dbo.Vehicle vehicle2_ 
                on vehicles6_.ID=vehicle2_.VehicleID 
        WHERE
            this_0_.type=1 
            AND manager1_.ManagerId = @p1
    );
@p0 = 10 [Type: Int32 (0)], @p1 = 34 [Type: Int32 (0)]

（我认为）正是我想要的。