linq 左連接後實現與主表一對一關係數據

 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();

結果：左連接 一對多 沒毛病

 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();

結果：左連接 一對一 

.Take()方法

 由此看出 使用.Take(1)方法在多表關聯後可以實現與主表一對一的關係數據來；根據業務需要也實現特定N的條數。