LINQ statement putting a select result (only 1) into a variable or an array

Question

Dear All,

I want to use a LINQ statement to put the result (only 1) into a variable or an array. Could any body help me?

Answer 1

If you have only record in the result, you can use FirstOrDefault. The FirstOrDefault returns the first element or the default valude if none exists. See the following example for your reference.

var names = new List<String> { "Hello" };
var firstName = names.FirstOrDefault();
Console.WriteLine($"First name is: {firstName}");

This will print the output Hello to the console.

Hope this helps

Answer 2

@BenTam-3003 , you can convert your table data to a datatable, then you can use linq to get the first element.

Here is a code example you could refer to.

string connstr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=School.accdb";  
    OleDbConnection connection = new OleDbConnection(connstr );  
    connection.Open();  
    string sql = "select * from Student";  
    OleDbDataAdapter adapter = new OleDbDataAdapter(sql, connection);  
    DataSet set=new DataSet();    
    adapter.Fill(set);  
    var table=set.Tables[0];  
    var result = table.AsEnumerable().Select(x => x.Field<int>("Age")).Take(1);  
    Console.WriteLine("First student Age is "+result.First());  

Result:

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Answer 3

This is easy with Entity Framework Core. You create classes using EF Power Tools, a free tool to reverse engineer your database.

Here I want the first record in a Customers table. The variable context is how we connect to the database.

private static async Task GetFirstRecord()
{
    await using var context = new NorthwindContext();
    var firstRecord = await context.Customers.FirstOrDefaultAsync();
    if (firstRecord is not null)
    {
        Debug.WriteLine(firstRecord.CustomerId);
    }
}

And the following using a Deconstruct from C#7 and higher

private static async Task GetFirstRecord()
{
    await using var context = new NorthwindContext();
    var (identifier, _) = await context.Customers.FirstOrDefaultAsync();
}

Answer 4

I created a code sample found here and shown below.

using System;  
using System.Threading.Tasks;  
using System.Windows.Forms;  
using Microsoft.EntityFrameworkCore;  
using StudentSimpleEntityFramework.Data;  
  
namespace StudentSimpleEntityFramework  
{  
    public partial class Form1 : Form  
    {  
        public Form1()  
        {  
            InitializeComponent();  
        }  
  
        private async void FirstOrDefaultIdButton_Click(object sender, EventArgs e)  
        {  
            await Task.Run(async () =>  
            {  
                await using (var context = new Context())  
                {  
                    var (identifier, _) = await context.Student.FirstOrDefaultAsync();  
                    MessageBox.Show($"First student id: {identifier}");  
                }  
            });  
        }  
  
        private async void FirstOrDefaultIdNameButton_Click(object sender, EventArgs e)  
        {  
            await Task.Run(async () =>  
            {  
                await using (var context = new Context())  
                {  
                    var (identifier, name) = await context.Student.FirstOrDefaultAsync();  
                    MessageBox.Show($"First student id: {identifier}\nName: {name}");  
                }  
            });  
        }  
  
        private async void FindByIdButton_Click(object sender, EventArgs e)  
        {  
            int studentIdentifier = 1;  
  
            await Task.Run(async () =>  
            {  
                await using (var context = new Context())  
                {  
                    var (identifier, name) = await context.Student.FindAsync(studentIdentifier);  
                    MessageBox.Show($"First student id: {identifier}\nName: {name}");  
                }  
            });  
        }  
    }  
}  
  

See this in the Student model which how only id or id and name are returned above.

public void Deconstruct(out int identifier, out string name)  
{  
    identifier = StudentId;  
    name = StudentName;  
}  

Answer 5

Here is a .NET Framework 4.8 code sample.

For your project

• From package manager console: Install-Package EntityFramework -Version 6.0.0
• Right click your project, add new
• Select from Data tab then as per image, continue, follow the prompts