linq 左连接后实现与主表一对一关系数据

 1 var query1 = 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()
 4 where r.Id == 655 || r.Id == 654
 5 select new
 6 {
 7 resId = r.Id,
 8 Id = ir.Id
 9 }; 
10 var sum1 = query1.Count();

结果：左连接 一对多 没毛病

  var query = from r in _residentRepository.GetAll()
                            join i in _inLogRepository.GetAll() on r.Id equals i.ResidentId into tmp_ir
                            from ir in tmp_ir.DefaultIfEmpty().Take(1)
                            where r.Id == 655 || r.Id == 654
                            select new
                            {
                                resId = r.Id,
                                Id = ir.Id
                            };
 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。