linq 左连接后实现与主表一对一关系数据

 1  1 var query1 = from r in _residentrepository.getall()
 2  2 join i in _inlogrepository.getall() on r.id equals i.residentid into tmp_ir
 3  3 from ir in tmp_ir.defaultifempty()
 4  4 where r.id == 655 || r.id == 654
 5  5 select new
 6  6 {
 7  7 resid = r.id,
 8  8 id = ir.id
 9  9 }; 
10 10 var sum1 = query1.count();

结果：左连接 一对多 没毛病

 1   var query = from r in _residentrepository.getall()
 2                             join i in _inlogrepository.getall() on r.id equals i.residentid into tmp_ir
 3                             from ir in tmp_ir.defaultifempty().take(1)
 4                             where r.id == 655 || r.id == 654
 5                             select new
 6                             {
 7                                 resid = r.id,
 8                                 id = ir.id
 9                             };
10  var sum = query.count();

结果：左连接 一对一 

.take()方法

 由此看出 使用.take(1)方法在多表关联后可以实现与主表一对一的关系数据来；根据业务需要也实现特定n的条数。