nhibernate:选择父母和最新的孩子 [英] nhibernate: select parents and newest child

问题描述

我有以下实体

public class Vehicle
{
    public virtual string InternalNumber { get; set; }
    public virtual IList<VehicleDriverHistory> DriverHistory { get; set; }
}

public class VehicleDriverHistory : HistoryEntity
{
    public virtual Vehicle Vehicle { get; set; }
    public virtual DriverPerson Driver { get; set; }
    public virtual DateTime Date { get; set; }
}

现在，我需要根据日期"选择每辆车，如果有的话，选择最新的VehicleDriverHistory-Entry. 但是我有点挣扎，我在sql中没问题，但是到目前为止在nhibernate中都失败了.

Now I need to select every Vehicle and, if present, the newest VehicleDriverHistory-Entry according to "Date". But I'm kinda struggling, I have no problem doing it in sql, but failed in nhibernate so far.

到目前为止我所拥有的:

What I have so far:

VehicleDriverHistory vdHistory = null;
VehicleDriverHistory vdHistory2 = null;
q.Left.JoinAlias(x => x.DriverHistory, () => vdHistory);
q.Left.JoinAlias(x => x.DriverHistory, () => vdHistory2).Where(x => vdHistory2.Date > vdHistory.Date);
q.Where(x => vdHistory2.Id == null);

这不起作用，这只是我尝试将sql查询(产生正确的数据)翻译"为nhibernate.

This doesn't work and it was just my attempt to "translate" the sql query (which yields the correct data) to nhibernate.

所以，我将如何选择父母和最新的孩子(如果没有父母，则不选择)

So, how would I select parents and the newest child (or none if none is present)

谢谢

更新

在Firos的帮助下，我得出了以下结论:

With Firos help I ended up with the following:

VehicleDriverHistory historyAlias = null;
var maxDateQuery = QueryOver.Of<VehicleDriverHistory>()
                   .Where(h => h.Vehicle == historyAlias.Vehicle)
                   .Select(Projections.Max<VehicleDriverHistory>(h => h.Date));

var vehiclesWithEntry = DataSession.Current.QueryOver(() => historyAlias)
                        .WithSubquery.WhereProperty(h => h.Date).Eq(maxDateQuery)
                        .Fetch(h => h.Vehicle).Eager
                        .Future();

Vehicle VehicleAlias = null;
var vehiclesWithoutEntry = DataSession.Current.QueryOver<Vehicle>(() => VehicleAlias)
                           .WithSubquery
                           .WhereNotExists(QueryOver.Of<VehicleDriverHistory>()
                           .Where(x => x.Vehicle.Id == VehicleAlias.Id).Select(x => x.Id))
                           .Future();

return vehiclesWithEntry.Select(h => new PairDTO { Vehicle = h.Vehicle, NewestHistoryEntry = h }).Concat(vehiclesWithoutEntry.Select(v => new PairDTO { Vehicle = v })).ToList();

我不得不用子查询子句替换vehclesWithoutEntry中的Any()语句，因为它引发了异常.

I had to replace the Any() statement in vehclesWithoutEntry with a subquery-clause because it raised an exception.

推荐答案

使用期货仅进行一次往返的其他想法

some other idea using Futures to make only one roundtrip

VehicleDriverHistory historyAlias = null;
var maxDateQuery = QueryOver.Of<VehicleDriverHistory>()
    .Where(h => h.Vehicle == historyAlias.Vehicle)
    .Select(Projections.Max<VehicleDriverHistory>(h => h.Date));

var vehiclesWithEntry = session.QueryOver(() => historyAlias)
    .WithSubquery.WhereProperty(h => h.Date).Eq(maxDateQuery)
    .Fetch(h => h.Vehicle).Eager
    .Select(h => new PairDTO { Vehicle = h.Vehicle, NewestHistoryEntry = h })
    .Future<PairDTO>();

var vehiclesWithoutEntry = session.QueryOver<Vehicle>()
    .Where(v => !v.DriverHistory.Any())
    .Select(v => new PairDTO{ Vehicle = v })
    .Future<PairDTO>();

return vehiclesWithoutEntry.Concat(vehiclesWithEntry); // .ToList() if immediate executing is required

更新:我无法重现异常，但是您可以尝试

Update: i can not reproduce the exception but you could try this

VehicleDriverHistory historyAlias = null;
var maxDateQuery = QueryOver.Of<VehicleDriverHistory>()
    .Where(h => h.Vehicle == historyAlias.Vehicle)
    .Select(Projections.Max<VehicleDriverHistory>(h => h.Date));

var vehiclesWithEntry = session.QueryOver(() => historyAlias)
    .WithSubquery.WhereProperty(h => h.Date).Eq(maxDateQuery)
    .Fetch(h => h.Vehicle).Eager
    .Future();

var vehiclesWithoutEntry = session.QueryOver<Vehicle>()
    .Where(v => !v.DriverHistory.Any())
    .Select(v => new PairDTO{ Vehicle = v })
    .Future<PairDTO>();

return vehiclesWithoutEntry.Select(h => new PairDTO { Vehicle = h.Vehicle, NewestHistoryEntry = h }).Concat(vehiclesWithEntry);

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