LINQ文查询，一对多的关系，请教！！！急！
主表有多条符合条件的数据class和student是1:M的关系
类 class
id claseName grade
1001 三年一班 三年级
1002 三年二班 三年级
1003 四年一班 四年级
类 student
id classId age
1001 1002 8
1002 1002 9
1003 1002 9
查出三年级，年龄大于等于9的学生信息
已从数据库查询出来一个list<class>，无条件查询出来的
现在要进行筛选，查出三年二班，年龄大于等于9的学生信息
要求写成list.where(...)形式，不是写成from p in list...
谢谢各位！！！ --------------------编程问答-------------------- liststu=liststu.Where(t=>t.age>=9&&t.classId==listclass.First(tt=>tt.claseName=="三年二班").id).ToList(); --------------------编程问答-------------------- var ary=listclass.Where(t=>t.grade=="三年级").Select(t=>t.id).ToArray();
liststu=liststu.Where(t=>t.age>=9&&ary.Contains(t.classId)).ToList(); --------------------编程问答-------------------- 楼上的可以
之前有一帖一样的
需求看似明了，是不是 还没表达清楚？楼主所说的 主表 是哪个表？
linq 是 to sql 还是 to Entity？
--------------------编程问答--------------------
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Class
{
public int ID { get; set; }
public string Name { get; set; }
}
class Student
{
public int ID { get; set; }
public int ClassID { get; set; }
public int Age { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<Class> classes = new List<Class>()
{
new Class() { ID = 0, Name = "二年一班" },
new Class() { ID = 1, Name = "二年二班" },
new Class() { ID = 2, Name = "三年一班" },
new Class() { ID = 3, Name = "三年二班" },
new Class() { ID = 4, Name = "四年一班" },
new Class() { ID = 5, Name = "四年二班" }
};
List<Student> students = new List<Student>()
{
new Student() { ID = 0, ClassID = 1, Age = 7 },
new Student() { ID = 1, ClassID = 2, Age = 8 },
new Student() { ID = 2, ClassID = 2, Age = 9 },
new Student() { ID = 3, ClassID = 3, Age = 9 },
new Student() { ID = 4, ClassID = 3, Age = 8 },
new Student() { ID = 5, ClassID = 3, Age = 9 },
new Student() { ID = 6, ClassID = 3, Age = 10 },
new Student() { ID = 7, ClassID = 4, Age = 9 },
new Student() { ID = 8, ClassID = 5, Age = 10 },
new Student() { ID = 9, ClassID = 5, Age = 10 },
};
var query = classes.GroupJoin(students, x => x.ID, x => x.ClassID, (g, s) => new { ClassID = g.ID, ClassName = g.Name, Students = s });
foreach (var item in query)
{
Console.WriteLine("name = {0}, id = {1}, students: {{ {2} }}.", item.ClassName, item.ClassID, string.Join("; ", item.Students.Select(x => string.Format("{{ id = {0}, age = {1} }}", x.ID, x.Age))));
}
var query1 = classes.GroupJoin(students, x => x.ID, x => x.ClassID, (g, s) => new { ClassID = g.ID, ClassName = g.Name, Students = s }).SelectMany(x => x.Students, (x, y) => new { x.ClassName, y.Age, y.ID, x.ClassID }).Where(x => x.ClassName == "三年二班" && x.Age >= 9);
foreach (var item in query1)
{
Console.WriteLine("id {0}. classid {1}. age {2}.", item.ID, item.ClassID, item.Age);
}
}
}
}
name = 二年一班, id = 0, students: { }.
name = 二年二班, id = 1, students: { { id = 0, age = 7 } }.
name = 三年一班, id = 2, students: { { id = 1, age = 8 }; { id = 2, age = 9 } }.
name = 三年二班, id = 3, students: { { id = 3, age = 9 }; { id = 4, age = 8 }; {
id = 5, age = 9 }; { id = 6, age = 10 } }.
name = 四年一班, id = 4, students: { { id = 7, age = 9 } }.
name = 四年二班, id = 5, students: { { id = 8, age = 10 }; { id = 9, age = 10 }
}.
id 3. classid 3. age 9.
id 5. classid 3. age 9.
id 6. classid 3. age 10.
Press any key to continue . . .
补充：.NET技术 , LINQ
