Question

我目前有这个linq声明..

Dim results = (From pb In db.ParcelBases
               Join l In db.LegalDescs On pb.lrsn Equals l.LRSN
               Join sh In db.SalesHists On pb.lrsn Equals sh.lrsn
               Where sh.sale_date >= dateFrom
               Where sh.sale_date <= dateTo
               Where sh.sale_amt >= psfldLow
               Where sh.sale_amt <= psfldHigh
               Select New With {
                 pb.lrsn,
                 pb.prop_street,
                 pb.owner1,
                 l.LEG_DESCRIPTION,
                 pb.parcel_id
               }).ToList

但是，我还需要搜索大约7个可选字段。做这个的最好方式是什么？我是否必须检查这些字段是否为空并为每个检查创建一个语句？或者有没有办法在声明中做到这一点？声明中当前的那些是最小选择所需的必填字段。

更新：我试图完成这样的事情..

Dim results = (From pb In db.ParcelBases
               Join l In db.LegalDescs On pb.lrsn Equals l.LRSN
               Join sh In db.SalesHists On pb.lrsn Equals sh.lrsn
               Where sh.sale_date >= dateFrom 'required field
               Where sh.sale_date <= dateTo   'required field
               Where sh.sale_amt >= psfldLow  'required field
               Where sh.sale_amt <= psfldHigh 'required field
               Where pb.propcity = tbPropCity 'optional field-could be null
               Where pb.proptype = tbPropType 'optional field-could be null
               Select New With {
                 pb.lrsn,
                 pb.prop_street,
                 pb.owner1,
                 l.LEG_DESCRIPTION,
                 pb.parcel_id
               }).ToList

Answer 1

您的意思是Or声明，例如：

Dim results = (From pb In db.ParcelBases
               Join l In db.LegalDescs On pb.lrsn Equals l.LRSN
               Join sh In db.SalesHists On pb.lrsn Equals sh.lrsn
               Where (sh.sale_date >= dateFrom
               And (sh.sale_date <= dateTo) 
               And (sh.sale_amt >= psfldLow)
               And (sh.sale_amt <= psfldHigh) 
Or (tbPropCity <> Nothing and  pb.propcity = tbPropCity) ' check for nulls here if necessary or something else Or... etc. )
                   Select New With {
                     pb.lrsn,
                     pb.prop_street,
                     pb.owner1,
                     l.LEG_DESCRIPTION,
                     pb.parcel_id
                   }).ToList

至少它听起来像你在寻找

Answer 2

您可以使用可选字段制作视图模型。

public class Thing {
    public type lrsn {get;set;}
    public type prop_street {get;set;}
    public type owner1 {get;set;}
    public type LEG_DESCRIPTION {get;set;}
    public type? propcity {get;set;}
    public type? proptype {get;set;}

    public Thing(
         type lrsn,
         type prop_street,
         type owner1,
         type LEG_DESCRIPTION,
         type? propcity = null,
         type? proptype = null)
    {
         this.lrsn = lrsn;
         this.prop_street = prop_street;
         this.owner1 = owner1;
         this.LEG_DESCRIPTION;
         this.propcity = propcity;
         this.proptype = proptype;
    }
}

然后你的代码在哪里：

using namespace.Thing;

Dim results = (From pb In db.ParcelBases
           Join l In db.LegalDescs On pb.lrsn Equals l.LRSN
           Join sh In db.SalesHists On pb.lrsn Equals sh.lrsn
           Where sh.sale_date >= dateFrom
           Where sh.sale_date <= dateTo
           Where sh.sale_amt >= psfldLow
           Where sh.sale_amt <= psfldHigh
           Select New Thing(
             pb.lrsn,
             pb.prop_street,
             pb.owner1,
             l.LEG_DESCRIPTION,
             pb.parcel_id
           )).ToList

Linq语句选择具有多个连接的可选字段

2 个答案: