假设，我们有一个类StationCat，它的具体属性如下：
public class StationCat
{
public string CustomerModel { get; set; }
public string baj_cZZLINE { get; set; }
public string IssuePosition { get; set; }
public string fact { get; set; }
public int InputCount { get; set; }
public int RepCount { get; set; }
public string S_NM { get; set; }
}此时，我们有2个由这个类实例化出的实体数组SWAPMaterials和StationCats，当我们想要把SWAPMaterials左连接到StationCats时，条件为SWAPMaterials表中元素的CustomerModel、baj_cZZLINE、S_NM与StationCats表元素对应的属性相等，那我们应该按照如下方式写LINQ
var resSWAPMaterials = (from p in SWAPMaterials
join StationCat in StationCats on new { p.CustomerModel, p.baj_cZZLINE,p.S_NM } equals new { StationCat.CustomerModel,StationCat.baj_cZZLINE,StationCat.S_NM } into p_StationCat
from StationCat_join in p_StationCat.DefaultIfEmpty()
select new StationCat()
{
CustomerModel = p.CustomerModel,
baj_cZZLINE = p.baj_cZZLINE,
IssuePosition = p.IssuePosition,
fact = p.fact,
RepCount = p.RepCount,
S_NM = p.S_NM,
InputCount = StationCat_join == null ? 0 : StationCat_join.InputCount
}).ToList();到此，我们就实现了Linq多条件字段的多表连接