public void Run2()
{
LinqDemoEntities db = new LinqDemoEntities();
var data = db.Student
.GroupJoin(
db.Course,
std => std.Id,
crs => crs.SutdentId,
(std, crs) => new { std.Id, std.Name, crs = crs }
)
.SelectMany(
x => x.crs.DefaultIfEmpty(), //要使用DefaultIfEmpty，才能轉換成Left Join
(std, crs) => new
{
std.Id, //輸出Student Id
std.Name, //輸出Student Name
crs.CourseName //輸出Course CourseName
}
);
foreach (var item in data)
{
Console.WriteLine(item.Id);
}
}
public void Run()
{
LinqDemoEntities db = new LinqDemoEntities();
var data = db.Student.SelectMany(x => x.Course.DefaultIfEmpty());
foreach (var item in data)
{
Console.WriteLine(item.CourseName);
}
Console.WriteLine("hi");
}
public void RunJoin()
{
LinqDemoEntities db = new LinqDemoEntities();
var data = db.Student
.Join(
db.Course, //跟Course LEFT JOIN
std => std.Id, //Student 對應Course Key 值為 Id
crs => crs.SutdentId, //Course 對應Student Key 值為SutdentId
(std, crs) => new {
std.Id, //輸出學生Id
std.Name, //輸出學生姓名
crs.CourseName //輸出課程名稱
}
);
}
