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📜  LINQ SingleOrDefault方法

📅  最后修改于: 2021-01-06 05:34:25             🧑  作者: Mango

LINQ SingleOrDefault方法

在LINQ中，SingleOrDefault()方法用于返回单个元素。如果列表/集合中不存在任何元素，则它将返回多个元素，并且将引发异常，如Single()方法。

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 objStudent = new List()
            {
                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 5
                int[] vs = { 1, 2, 3, 4, 5 };
    //objStudent.SingleOrDefault() method will return the information of the student
                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; }
        }
}

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：

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 objStudent = new List()
           {
                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 5
            int[] objList = { 1, 2, 3, 4, 5 };
    //here SingleOrDefault()method will return the default value
            int 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 ”返回多个值。

输出：