Group Join 操作

Posted wuyicqb

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了Group Join 操作相关的知识,希望对你有一定的参考价值。

GroupJoin

The GroupJoin operator performs the same task as Join operator except that GroupJoin returns a result in group based on specified group key.
The GroupJoin operator joins two sequences based on key and groups the result by matching key and then returns the collection of grouped result and key.

Example

public class Student {
	public int StudentID {get;set;}
	public string StudentName {get;set;}
	public int StandardID {get;set;}
}

public class Standard {
	public int StandardID{get;set;}
	public string StandardName{get;set;}
}

IList<Student> studentList =newList<Student>(){
	newStudent() { StudentID = 1, StudentName = "John", StandardID = 1 },
	newStudent() { StudentID = 2, StudentName = "Moin" ,StandardID = 1 },
	newStudent() { StudentID = 3, StudentName = "Bill" ,StandardID = 2 },
	newStudent() { StudentID = 4, StudentName = "Ram" ,StandardID = 2 },
	newStudent() { StudentID = 5, StudentName = "Ron" }
};

IList<Standard> standardList = newList<Standard>(){
	newStandard() { StandardID = 1, StandardName = "Standard 1" },
	newStandard() { StandardID = 2, StandardName = "Standard 2" },
	newStandard() { StandardID = 3, StandardName = "Standard 3" }
};

var groupJoin = standardList.GroupJoin(studentList,//inner sequence
	std => std.StandardID,//outerKeySelector
	s => s.StandardID,//innerKeySelector
	(std, studentsGroup) => new// resultSelector
	{
		Students = studentsGroup,
		StandarFulldName = std.StandardName
	});

foreach(var item in groupJoin)
{
	Console.WriteLine(item.StandarFulldName);
	foreach(var stud in item.Students)
	Console.WriteLine(stud.StudentName);
}

Results:

Standard1:
John,
Moin,
Standard2:
Bill,
Ram,
Standard3:

以上是关于Group Join 操作的主要内容,如果未能解决你的问题,请参考以下文章

thinkphp中join用法

linq group join

SQL 效率:WHERE IN 子查询与 JOIN 然后 GROUP

kafkaThe group member needs to have a valid member id before actually entering a consumer group(代码片段

MYSQL - 将 SUM 与 JOIN 结合使用

SQL GROUP BY 或 JOIN