Group Join 操作

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: