4

C#进阶-LINQ实现对集合的增删改查

 4 months ago
source link: https://blog.51cto.com/liuguangzhi/10682421
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
neoserver,ios ssh client

前面的章节细致介绍了LINQ扩展包的具体方法使用，本篇则是演示LINQ在日常开发中的常用操作，实现结果集的增删改查。目前LINQ支持两种语法，我会在每个案例前先用大家熟知的SQL语句表达，再在后面用C#的两种LINQ语法分别实现。LINQ语法第一次接触难免感到陌生，最好的学习方式就是在项目中多去使用，相信会有很多感悟。

一、LINQ表达式学前准备

在学习之前，我们要做一些准备工作，我们需要创建User对象和包含User对象的集合，作为后面查询和输出的数据源。

1、C#代码准备

C#类：

class User
{
    public int id { get; set; } 
    public string name { get; set; } 
    public bool gender { get; set; }//male: true; female: fasle
    public int age { get; set; }
    public string occupation { get; set; } //职业
}
List<User> list = new List<User>()
{
    new User { id = 1, name = "Zhang Long", age = 38, gender = true, occupation = "Teacher"},
    new User { id = 2, name = "Zhang Jin", age = 18, gender = false, occupation = "Student"},
    new User { id = 3, name = "Zhang Shuai", age = 38, gender = false, occupation = "Teacher"},
    new User { id = 4, name = "Liu Guangzhi", age = 38, gender = false, occupation = "Doctor"},
    new User { id = 5, name = "Liu Ziming", age = 38, gender = true, occupation = "Doctor"},
    new User { id = 6, name = "Liu Shuai", age = 29, gender = false, occupation = "Doctor"},
    new User { id = 7, name = "Liu Jin", age = 21, gender = true, occupation = "Builder"},
    new User { id = 8, name = "Jiang Long", age = 38, gender = true, occupation = "Builder"},
    new User { id = 9, name = "Hu Ziming", age = 21, gender = true, occupation = "Student"},
    new User { id = 10, name = "Hu Jin", age = 21, gender = false, occupation = "Student"}
};

2、数据库准备

数据源1：

C#进阶-LINQ实现对集合的增删改查_List

数据源2：

C#进阶-LINQ实现对集合的增删改查_List_02

二、LINQ对集合增删改查语法

Linq是对集合进行操作，这里列举对集合增删改查的常用方法。在学习之前，我们要做一些准备工作，我们需要创建User对象和包含User对象的集合，创建Salary对象和包含Salary对象的集合，作为后面查询和输出的数据源。

1、新增集合内对象

/* 新增一个任意属性的用户到集合 */
/* C#版本1 */
 User userAdd = new User() {
  id = 11,
  name = "Liu Mingxiu",
  age = 22,
  gender = false,
  occupation = "Doctor"
};
list.Add(userAdd);

/* C#版本2(支持一次添加多个) */
IEnumerable<User> userAddList = new List<User>().Append(userAdd);
list.AddRange(userAddList);
/* 输出结果 */
{id = 1, name = Zhang Long, age = 38, gender = True, occupation = Teacher}, 
{id = 2, name = Zhang Jin, age = 18, gender = False, occupation = Student}, 
{id = 3, name = Zhang Shuai, age = 38, gender = False, occupation = Teacher}, 
{id = 4, name = Liu Guangzhi, age = 38, gender = False, occupation = Doctor}, 
{id = 5, name = Liu Ziming, age = 38, gender = True, occupation = Doctor}, 
{id = 6, name = Liu Shuai, age = 29, gender = False, occupation = Doctor}, 
{id = 7, name = Liu Jin, age = 21, gender = True, occupation = Builder}, 
{id = 8, name = Jiang Long, age = 38, gender = True, occupation = Builder}, 
{id = 9, name = Hu Ziming, age = 21, gender = True, occupation = Student}, 
{id = 10, name = Hu Jin, age = 21, gender = False, occupation = Student}, 
{id = 11, name = Liu Mingxiu, age = 22, gender = False, occupation = Doctor}

2、更新集合内的指定对象属性

这里是把原有的User集合中每个User的name属性提取出来，组成一个全是name的新的集合，故新集合为String属性。

/* 修改集合内所有医生的工资为10000且在职 */
/* C#版本1 使用ForEach方法 */
salaryList.Where(item => item.occupation == "Doctor").ToList()
                .ForEach(u => { u.salary = 10000; u.active = true; });

/* C#版本2 使用All方法(需要返回true) */
salaryList.Where(item => item.occupation == "Doctor").ToList()
                .All( u => { u.salary = 10000; u.active = true; return true; });
/* 输出结果 */
{id = 1, name = Zhang Long, occupation = Teacher, active = True, salary = 7800}
{id = 2, name = Zhang Jin, occupation = Student, active = True, salary = 1500}
{id = 3, name = Zhang Shuai, occupation = Teacher, active = False, salary = 8800}
{id = 4, name = Liu Guangzhi, occupation = Doctor, active = True, salary = 10000}
{id = 5, name = Liu Ziming, occupation = Doctor, active = True, salary = 10000}
{id = 6, name = Liu Shuai, occupation = Doctor, active = True, salary = 10000}
{id = 7, name = Liu Jin, occupation = Builder, active = True, salary = 7000}
{id = 8, name = Jiang Long, occupation = Builder, active = False, salary = 8500}
{id = 9, name = Hu Ziming, occupation = Student, active = True, salary = 2100}
{id = 10, name = Hu Jin, occupation = Student, active = True, salary = 1300}

3、删除集合内指定对象

/* 删除集合内所有职业为医生的用户对象 */

/* 推荐使用RemoveAll方法批量删除 */
/* C#版本1 */
list.RemoveAll(item => item.occupation == "Doctor");

/* 也可以使用Remove方法单个删除 */
/* C#版本2 */
List<User> maps = list.Where(item => item.occupation == "Doctor").ToList();
foreach (User userDelete in maps){
  list.Remove(userDelete);
}

/* C#版本3 */
List<User> maps = (from u in list where u.occupation == "Doctor" select u).ToList();
foreach (User userDelete in maps){
  list.Remove(userDelete);
}
/* 输出结果 */
{id = 1, name = Zhang Long, age = 38, gender = True, occupation = Teacher}, 
{id = 2, name = Zhang Jin, age = 18, gender = False, occupation = Student}, 
{id = 3, name = Zhang Shuai, age = 38, gender = False, occupation = Teacher}, 
{id = 7, name = Liu Jin, age = 21, gender = True, occupation = Builder}, 
{id = 8, name = Jiang Long, age = 38, gender = True, occupation = Builder}, 
{id = 9, name = Hu Ziming, age = 21, gender = True, occupation = Student}, 
{id = 10, name = Hu Jin, age = 21, gender = False, occupation = Student}

4、查询集合内的对象

基础查询参考： C#进阶-LINQ表达式基础语法；

多表查询参考： 多表查询 Ⅰ(交集、并集、差集、去重)、 多表查询 Ⅱ(Join连接查询)；

分组查询参考： 分组查询 (GroupBy)；

三、LINQ对集合增删改查总结

LINQ（Language Integrated Query）提供了强大的查询能力，主要用于读取和检索数据集合中的信息。虽然LINQ自身不直接支持修改操作（增、删、改），但它可以与其他.NET功能如List<T>的方法配合使用，来实现集合的完整管理。下面将详细介绍如何结合LINQ进行集合的增删改查操作。通过与.NET的集合操作结合，LINQ可以实现对数据集合的全面管理。这种方式的优势在于能够利用LINQ强大的查询能力来选择操作的目标，从而使数据操作更加精确和高效。在实际应用中，理解LINQ与传统集合方法的结合使用是非常重要的。


report

Recommend

About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK