C#--LINQ--2--LINQ高级查询

以下是学习笔记：

1，聚合类查询

【1】

 

 【2】

 

 2，排序类

 

 3，分区类

nums.Skip(1).Take(3):跳过1个取3个，所以结果就是2，3，4

 

 

4，集合类查询

感受一下：去重功能太强大了，一行代码搞定

 

 

5，生成类查询

 

 6，总结：

 

以下转载 

https://www.cnblogs.com/fangjb/p/15843213.html

c#中如何使用到模糊查询,先举个最简单实用的例子，可在vs控制台应用程序中输出：

定义实体类：

 public class Student
        {
            public int ID { get; set; }

            public string Name { get; set; }

            public int? Age { get; set; }

            public string Sex { get; set; }
        }

 

为实体类赋值存放到集合list中：

 List<Student> lsStudent = new List<Student>(){
                new Student { ID = 1,Name = "1", Age = 128, Sex = null },
                new Student { ID = 2, Name = "2", Age = 18, Sex = "女" },
                new Student { ID = 3, Name = "31", Age = 13, Sex = "男" },
                new Student { ID = 4, Name = "4", Age = 23, Sex = "男" },
                new Student { ID = 5, Name = "51", Age = null, Sex = "女" },
                new Student { ID = 6, Name = "6", Age = null, Sex = "女" },
                new Student { ID = 7, Name = "7", Age = null, Sex = "女" }

            };

模糊查询条件：根据Name=1或者Sex=女模糊查询

   string key = "1";
   string sex = "女";

  方法一：linq

   List<Student> resultList = (from c in lsStudent where  c.Name.Contains(key) ||c.Sex.Contains(sex) select c).ToList();

  知识讲解：

  1,Contains("key"),---意义等同于ql server中的like '%key%'，从两端模糊匹配

  2,StartsWith("key"),---意义等同于sql server中的like 'key%',从开头模糊匹配

  3,EndsWith("key"),---意义等同于sql server中的like '%key',从结尾模糊匹配

 

要实现字符串的精确匹配，可以用 == 

from c in lsStudent where  c.Name == "key"

 

 

 方法二：
   List<Student> resultList = lsStudent.Where(str => str.Name.Contains(key) || str.Sex.Contains(key)).ToList();

 

  方法三：
   List<Student> resultList = (from c in lsStudent where c.Name.IndexOf(key)>=0 ||c.Sex.IndexOf(sex)>=0 select c).ToList();

  知识讲解：

  1，c.Name.IndexOf(key)>=0 ---意义等同于 like '%key%',从两端模糊匹配

  2，c.Name.StartsWith(key) ---等同于like 'key%' ,从开头模糊匹配

  3，c.Name.EndWith(key) ---等同于like '%key',从结尾模糊匹配

  vs控制台输出打印代码：

 

  string json = JsonConvert.SerializeObject(resultList, Newtonsoft.Json.Formatting.Indented);
  Console.WriteLine(json);

 

https://www.cnblogs.com/alunchen/p/6829460.html

 

List<User> users1 = new List<User>();
            users1.Add(new User() {Id = 1, Age = 1, Name = "Name01"});
            users1.Add(new User() { Id = 2, Age = 2, Name = "Name02" });
            users1.Add(new User() { Id = 3, Age = 3, Name = "Name03" });
            users1.Add(new User() { Id = 4, Age = 4, Name = "Name04" });

            List<User> users2 = new List<User>();
            users2.Add(new User() { Id = 4, Age = 44, Name = "Name044" });
            users2.Add(new User() { Id = 5, Age = 55, Name = "Name01" });
            users2.Add(new User() { Id = 6, Age = 66, Name = "Name06" });
            users2.Add(new User() { Id = 7, Age = 77, Name = "Name07" });
            users2.Add(new User() { Id = 8, Age = 88, Name = "Name08" });

            //把两个list合并在一起
            var result1 = new List<User>();
            result1.AddRange(users1);
            result1.AddRange(users2);

            //去重：在result1中去重
            var result2 = result1.Distinct().ToList();

            //差集：users1在users2之中的差集
            var result3 = users1.Except(users2).ToList();

            //并集：users1与users2 合起来不重复的元素
            var result4 = users1.Union(users2).ToList();

            //交集：users1与users2 相同的元素
            var result5 = users1.Intersect(users2).ToList();