Question

我正在尝试进行左连接，即1条用户记录与1条记录（如果有）联系在一起。运行此命令时，它仍然拉多个联系人，而忽略了我的条件“ where c.RecordType ==“ USR””。

 public class Users
{
    public int Id { get; set; }
    ... other properties

     public Contact Contact { get; set; }
}

    public class Contact
{
    public int Id { get; set; }
    public int RecordID { get; set; }
    public string RecordType { get; set; }

    [ForeignKey("RecordID")]
    public Users User { get; set; } 
}

Linq查询

var query3 = (from c in db1.Contacts
                      join u in db1.Users
                      on c.RecordID equals u.Id
                      into a
                      from b in a.DefaultIfEmpty(new Models.Users())
                      where c.RecordType == "USR"
                      && b.Lastname.Contains(name)
                      && b.Active == 1
                      select new
                      {
                          b.Id,
                          b.FirstName,
                          b.Lastname,
                          b.FullName,
                          b.Contact                          
                      }).ToList();

对我要去哪里的任何帮助将不胜感激。

谢谢，亚当

Answer 1

您可以在linq中进行联接，而无需使用join关键字。我对左联接使用以下构造，没有任何问题。

var query3 = (from c in db1.Contacts
              from u in db1.Users.Where(x => c.RecordID == x.Id).DefaultIfEmpty() 
              where (c.RecordType == "USR")
                  && u.Lastname.Contains(name) && (u.Active == 1)
              select new
              {
                  u.Id,
                  u.FirstName,
                  u.Lastname,
                  u.FullName,
                  u.Contact                          
               }).ToList();

Answer 2

根据相关信息

1条用户记录中有1条（如果有）与之关联的联系人记录

意味着一个用户可以有零个或多个联系人，因此您假设将User用作主要实体，然后在Contacts上保留联接。另外，您还应该在JOIN本身期间应用Contact类型过滤器，如下所示

var query3 = (  join u in db1.Users
              from c in db1.Contacts 
                on new { Record = c.RecordID, Type = c.RecordType } equals new { Record = u.Id, Type = "USR"} into b
              from cont in b.DefaultIfEmpty(new Models.Contacts())
              where u.Lastname.Contains(name)
              && u.Active == 1
              select new
              {
                  u.Id,
                  u.FirstName,
                  u.Lastname,
                  u.FullName,
                  cont.Contact                          
              }).ToList();

左联接Linq查询条件未过滤

2 个答案: