本文概述
- LINQ SingleOrDefault()方法的语法
- LINQ SingleOrDefault()方法的示例
LINQ SingleOrDefault()方法的语法 这是使用LINQ SingleOrDefault()方法从集合中获取单个元素的语法。
int a = objList.SingleOrDefault();
在以上语法中, 我们将从集合” objList” 中返回单个元素。并且, 如果集合不包含任何元素, 则它将返回默认值。
LINQ SingleOrDefault()方法的示例 这是LINQ SingleOrDefault方法的示例, 当元素不存在于集合中时, 该方法可从集合中获取单个元素。
using System;
using System. Collections;
using System.Collections.Generic;
using System. Linq;
using System. Text;
using System.Threading.Tasks;
namespace ConsoleApp1{class Programme2{static void Main(string[] args){//create the object 'objStudnet' of the class 'Student' added the record to the list List<
Student>
objStudent = new List<
Student>
(){new Student() { Name = "Akshay Tyagi", Gender = "Male", Location="Chennai" }, new Student() { Name = "Vaishali Tyagi", Gender = "Female", Location="Chennai" }, new Student() { Name = "Arpita Rai", Gender = "Male", Location="Bangalore" }, new Student() { Name = "Shubham Rastogi", Gender = "Male", Location ="Vizag"}, new Student() { Name = "Aman Singhal", Gender = "Male", Location="Nagpur"}};
//initialize the array 'vs' from 1 to 5int[] vs = { 1, 2, 3, 4, 5 };
//objStudent.SingleOrDefault() method will return the information of the studentvar user = objStudent.SingleOrDefault(i =>
i.Name == "Akshay Tyagi");
string result = user.Name;
int val = vs.SingleOrDefault(j =>
j >
5);
Console.WriteLine("Element from objStudent: {0}", result);
Console.WriteLine("Element from objList: {0}", val);
Console.ReadLine();
}}class Student{public string Name { get;
set;
}public string Gender { get;
set;
}public string Location { get;
set;
}}}在上面的示例中, 我们尝试使用LINQ SingleOrDefault()方法从两个列表(objStudent, objList)对象中获取单个元素
输出
文章图片
如果列表/集合返回多个元素, 则LINQ SingleOrDefault()方法将引发InvalidOperationException错误。
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp1{class Programme2{static void Main(string[] args){List<
Student>
objStudent = new List<
Student>
(){new Student() { Name = "Akshay Tyagi", Gender = "Male", Location="Chennai" }, new Student() { Name = "Vaishali Tyagi", Gender = "Female", Location="Chennai" }, new Student() { Name = "Arpita Rai", Gender = "Male", Location="Bangalore" }, new Student() { Name = "Shubham Rastogi", Gender = "Male", Location ="Vizag"}, new Student() { Name = "Aman Singhal", Gender = "Male", Location="Nagpur"}};
//initialize the objList array from 1 to 5int[] objList = { 1, 2, 3, 4, 5 };
//here SingleOrDefault()method will return the default valueint val = objList.SingleOrDefault();
Console.WriteLine("Element from objList: {0}", val);
Console.ReadLine();
//int[] vs = { 1, 2, 3, 4, 5 };
//var user = objStudent.SingleOrDefault(i =>
i.Name == "Akshay Tyagi");
//string result = user.Name;
//int val = vs.SingleOrDefault(j =>
j >
5);
//Console.WriteLine("Element from objStudent: {0}", result);
//Console.WriteLine("Element from objList: {0}", val);
Console.ReadLine();
}}class Student{public string Name { get;
set;
}public string Gender { get;
set;
}public string Location { get;
set;
}}}如果我们运行上面的代码, 它将抛出InvalidOperationException错误, 因为” objlist” 返回了多个值。
输出
文章图片
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