ef 查询总结

Posted 2020-08-06 龙仪

1、Linq 查询两张表；a表和b表，要得到的数据是a表数据b表没有

例如：a表有5条数据1,2,3,4,5；b表有2条数据1,3；那么就用dataGridView1输出2,4,5；link语句要怎么写

 

from x in a where !b.Any(y=>y.id==x.id) select x;

 

------------------------------------- 转化成的sql类似如下

SELECT [t0].[ID] AS [ID] FROM [a] AS [t0] WHERE NOT (EXISTS( SELECT NULL AS [EMPTY] FROM [b] AS [t1] WHERE [t1].[ID] = [t0].[ID] )) 

 

这样b表中没有的就输出了。

2、Linq获取两个List或数组的差集交集

List<int> list1 = new List<int>();
list1.Add(1);
list1.Add(2);
list1.Add(3);
List<int> list2 = new List<int>();
list2.Add(3);
list2.Add(4);
list2.Add(5);
//得到的结果是4,5 即减去了相同的元素。
List<int> list3 = list2.Except(list1).ToList();
foreach (int i in list3)
{
    MessageBox.Show(i.ToString());
}

合并两个数组,并去掉重复元素,然后排序(C#)

List<int> numbers1 = new List<int>() { 5, 4, 1, 3, 9, 8, 6, 7, 12, 10 };
List<int> numbers2 = new List<int>() { 15, 14, 11, 13, 19, 18, 16, 17, 12, 10 };
var newQuerty = numbers1.Concat(
from n in numbers2
where !numbers1.Contains(n)
select n
).OrderBy(n=>n);

合并两个数组，并去除合并后的重复数据， 并排序

  int[] A={1,2,2,3,4,5,6,6,6};
            int[] B={2,2,2,3,7,8,9,5};

            List<int> list = new List<int>(A);
            list.AddRange(B);

            list.Sort();

            //去除重复项
            foreach (int i in list.Distinct<int>())
            {
                Console.WriteLine(i);
            }

C# 取两个数组的相同元素

以往我们都是肯定绞尽脑汁，肯定什么循环，元素大小，什么因素都考虑进去。但是现在采用Linq可以很好的解决这个问题。找出两个或多个数组的相同项。

代码相当简单：

usingSystem;

usingSystem.Collections.Generic;

usingSystem.Linq;

usingSystem.Text;

 

namespaceTest4_03

{

   classProgram

    {

       staticvoidMain(string[] args)

        {

           string[] names = {"Adams","Arthur","Buchanan","Tsbuchis","ShCian","FuchsiaLinda","DecheChen","Lotheer","FindLanciCade","SorchLand","JiangZheng","MisiiLoda","Gtod","Dfac","Lama","BakCades","Losangle","ZheWQ","GehengDahaLothi","ToryLandey","DakaLothy","BthLanda","MenNorth","Fith","FoxMain","DontM","Saobba","Del","Sala","Ghero","BhthLaPhda"};

           IEnumerable<string> skip = names.Skip(10);

           IEnumerable<string> take = names.Take(11);

 

           //取出两个序列中交集部分，按理论应该输出JiangZheng

           IEnumerable<string> intersect = skip.Intersect(take);

 

           foreach(varsinintersect)

            {

               Console.WriteLine(s);

            }

           Console.ReadKey();

        }

    }

}