先看一个最简单的inner join,在读取Student表时inner join Class表取的对应的Class信息:
static void Main(string[] args)
{
using (var writer = new StreamWriter(WatchSqlPath, false, Encoding.UTF8))
{
using (DbAppDataContext db = new DbAppDataContext())
{
db.Log = writer; //inner join
var query = from s in db.Students
join c in db.Classes on s.ClassID equals c.ClassID
where c.ClassID ==
select new
{
ClassID = s.ClassID,
ClassName = c.ClassName,
Student = new
{
Name = s.Name,
ID = s.StudentID
}
}; foreach (var item in query)
{
Console.WriteLine("{0} {1} {2}", item.ClassID, item.ClassName, item.Student.Name);
}
}
} Console.ReadLine();
}
特别简单,就不贴sql了,继续看outer join:
static void Main(string[] args)
{
using (var writer = new StreamWriter(WatchSqlPath, false, Encoding.UTF8))
{
using (DbAppDataContext db = new DbAppDataContext())
{
db.Log = writer; //left outer join
var query = from s in db.Students
join c in db.Classes on s.ClassID equals c.ClassID into gc
from gci in gc.DefaultIfEmpty()
select new
{
ClassID = s.ClassID,
ClassName = gci.ClassName,
Student = new
{
Name = s.Name,
ID = s.StudentID
}
};
foreach (var item in query)
{
Console.WriteLine("{0} {1} {2}", item.ClassID, item.ClassName, item.Student.Name);
}
}
} Console.ReadLine();
}
Outer join时必须将join后的表into到一个新的变量gc中,然后要用gc.DefaultIfEmpty()表示外连接。
linq to sql相关随笔:
1. 从CUD开始,如何使用LINQ to SQL插入、修改、删除数据
3. 查询 延迟加载与立即加载,使用LoadWith和AssociateWith
4. 查询 inner join,left outer join