本文介绍了转换SQL到LINQ与空左连接的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我怎么能这样的SQL转换成适当地LINQ
How can I convert properly this SQL to linq
select t1.ProgramID
from Program t1 LEFT JOIN ProgramLocation t2 ON t1.ProgramID = t2.ProgramID
where t2.ProgramID IS NULL
我尝试,但它不能正常工作
I try that but it not working
var progy = (
from u in db.ProgramLocations join b in db.Programs
on u.ProgramID equals b.ProgramID into yG
from y1 in yG.DefaultIfEmpty()
where u.ProgramID == null
where u.ProgramID == null
select u.ProgramID
).ToList();
谢谢
推荐答案
您想要使用 .DefaultIfEmpty
,按。
var query = from p in Programs
join pl in ProgramLocations
on p.ProgramID equals pl.ProgramID into pp
from pl in pp.DefaultIfEmpty()
where pl == null
select p;
下面是一个完整的,工作的例子有一些模拟数据对象:
Here's a full, working example with some mock data objects:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace LinqTest
{
class LinqProgram
{
public class Program
{
public int ProgramID { get; set; }
public string ProgramName { get; set; }
}
public class ProgramLocation
{
public int ProgramLocationID { get; set; }
public int ProgramID { get; set; }
public string ProgramLocationName { get; set; }
}
public static List<Program> Programs = new List<Program>();
public static List<ProgramLocation> ProgramLocations = new List<ProgramLocation>();
static void Main(string[] args)
{
FillTestData();
var query = from p in Programs
join pl in ProgramLocations
on p.ProgramID equals pl.ProgramID into pp
from pl in pp.DefaultIfEmpty()
where pl == null
select p;
foreach (var r in query)
{
Console.WriteLine("{0}: {1}", r.ProgramID, r.ProgramName);
}
Console.ReadLine();
}
private static void FillTestData()
{
var p = new Program()
{
ProgramID = Programs.Count + 1,
ProgramName = "Scary Lesson"
};
var pl = new ProgramLocation()
{
ProgramLocationID = ProgramLocations.Count + 1,
ProgramID = p.ProgramID,
ProgramLocationName = "Haunted House"
};
Programs.Add(p);
ProgramLocations.Add(pl);
p = new Program()
{
ProgramID = Programs.Count + 1,
ProgramName = "Terrifying Teachings"
};
pl = new ProgramLocation()
{
ProgramLocationID = ProgramLocations.Count + 1,
ProgramID = p.ProgramID,
ProgramLocationName = "Mystical Mansion"
};
Programs.Add(p);
ProgramLocations.Add(pl);
p = new Program()
{
ProgramID = Programs.Count + 1,
ProgramName = "Unassociated Program"
};
Programs.Add(p);
}
}
}
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