Linq和EF 做 單一條件查詢 和 復合條件 查詢 以及 多表 聯合查詢 示例

單一條件查詢：

var table2Object = (from t1 in db.table1
             join t2 in db.table2 on t1.id equals t2.id         
             select t2).FirstOrDefault();

 

復合條件 查詢：

多個主鍵 聯合查詢

var table2Object = (from t1 in db.table1
             join t2 in db.table2
             on new { t1.id, t1.another_id } equals new { t2.id, t2.another_id }
             select t2).FirstOrDefault();

多表聯合查詢：

Join3個Table

var table2Object = (from t1 in db.table1
             join t2 in db.table2
             on new { t1.id, t1.another_id } equals new { t2.id, t2.another_id }
             join t3 in db.table3
             on new { t2.id, t2.another_id } equals new { t3.id, t3.another_id }
             select t2).FirstOrDefault();