Question

我试图用XPO编写下一个MSSQL查询时已经打破了我的想法：

SELECT     Gate.Name, grp.maxDate as 'Latest pass', a.Type,  a.ReceivedTime as 'Imported at'
FROM       Access AS a INNER JOIN
                      (SELECT     GateId, MAX(OpenTime) AS maxDate
                        FROM      Access
                        GROUP BY GateId) AS grp ON a.GateId = grp.GateId AND a.OpenTime = grp.maxDate INNER JOIN
                  Gate ON a.GateId = Gate.ID
                  order by Gate.ID

My Access表有大约2个记录，但它只有40个不同的GateId。我想为每个门选择一条线，如下所示：
GateName OpenTime类型导入为 .................................................. ..................................
Supergate 20/09/2013 1 21/09/2013
Ultragate 19/09/2013 0 22/09/2013

我的Access类看起来像这样：

    public partial class Access : XPLiteObject
{
    Gate fGateId;
    [Association(@"AccessReferencesGate")]
    public Gate GateId
    {
        get { return fGateId; }
        set { SetPropertyValue<Gate>("GateId", ref fGateId, value); }
    }
    DateTime fOpenTime;
    public DateTime OpenTime
    {
        get { return fOpenTime; }
        set { SetPropertyValue<DateTime>("OpenTime", ref fOpenTime, value); }
    }
    byte fType;
    public byte Type
    {
        get { return fType; }
        set { SetPropertyValue<byte>("Type", ref fType, value); }
    }
    DateTime fReceivedTime;
    public DateTime ReceivedTime
    {
        get { return fReceivedTime; }
        set { SetPropertyValue<DateTime>("ReceivedTime", ref fReceivedTime, value); }
    }
    int fID;
    [Key(true)]
    public int ID
    {
        get { return fID; }
        set { SetPropertyValue<int>("ID", ref fID, value); }
    }
    public Access(Session session) : base(session) { }
}

My Gate课程：

public partial class Gate : XPLiteObject
{
    int fID;
    [Key(true)]
    public int ID
    {
        get { return fID; }
        set { SetPropertyValue<int>("ID", ref fID, value); }
    }
    string fName;
    [Size(20)]
    public string Name
    {
        get { return fName; }
        set { SetPropertyValue<string>("Name", ref fName, value); }
    }
    }
    [Association(@"AccessReferencesGate", typeof(Access))]
    public XPCollection<Access> AccessCollection { get { return GetCollection<Access>("AccessCollection"); } }
    public Gate(Session session) : base(session) { }
}

任何答案，甚至RTFM链接都将不胜感激！

Answer 1

像

这样的东西

var accesses = new XPQuery<Access>(session);
var result = 
    from a in accesses 
    where a.OpenTime == a.GateId.AccessCollection.Max(b => b.OpenTime) 
    select new { a.GateId.Name, a.Type, a.ReceivedTime };

Answer 2

DevExpress支持中心的回答，对我有用：

XPView view = new XPView(typeof(Access));
view.AddProperty("Name", "GateId.Name");
view.AddProperty("LatestPass", "[<Access>][GateId = ^.GateId].Max(OpenTime)");
view.AddProperty("Type", "Type");
view.AddProperty("ImportedAt", "ReceivedTime");
view.Criteria = CriteriaOperator.Parse("OpenTime = [<Access>][GateId = ^.GateId].Max(OpenTime)");

带有子选择的DevExpress XPO

2 个答案: