EF 查询表达式 join

佚名 6年前 (2019-05-06) 随笔 625人围观抢沙发百度已收录

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1.无into,相当于 inner join

var query = from p in context.P
                            join s in context.S on p.PID equals s.PID
                            select new { p.PNAME, s.SNAME };
                query.ToList().ForEach(x =>
                {
                    Console.WriteLine("{0} - {1}", x.PNAME, x.SNAME);
                });
                Console.WriteLine("数量:" + query.Count());
                Console.ReadLine();

结果:

2.有 into,类似于 left join,注意,返回了主表多条对应的数据

var query = from p in context.P
                            join s in context.S on p.PID equals s.PID
                            into ab
                            from abTable in ab.DefaultIfEmpty()
                            select new { p.PNAME, abTable.SNAME };
                query.ToList().ForEach(x =>
                {
                    Console.WriteLine("{0} - {1}", x.PNAME, x.SNAME);
                });
                Console.WriteLine("数量:" + query.Count());