08_Code First Approach with Dependency Injection and LINQ queries in .NET Console Application - Maniconserve/EF-Core GitHub Wiki

Step 1: Install Required Packages

To enable Dependency Injection and Entity Framework Core, install the following NuGet packages:

 Install-Package Microsoft.EntityFrameworkCore
 Install-Package Microsoft.EntityFrameworkCore.SqlServer
 Install-Package Microsoft.EntityFrameworkCore.Tools
 Install-Package Microsoft.Extensions.DependencyInjection
 Install-Package Microsoft.Extensions.Configuration.Json

Step 2: Configure Connection String in appsettings.json

Instead of hardcoding the connection string, store it in an appsettings.json file.

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=YOUR_SERVER;Database=SchoolDB;Trusted_Connection=True;TrustServerCertificate=True;"
  }
}

Step 3: Define the Student Entity

Create a model to represent the Students table.

using System.ComponentModel.DataAnnotations;

public class Student
{
    [Key]
    public int Id { get; set; }
    
    [Required]
    public string Name { get; set; }
    
    public int Age { get; set; }
    
    public string Grade { get; set; }
}

Step 4: Create the ApplicationDbContext

Define the database context to manage the Students table.

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;

public class ApplicationDbContext : DbContext
{
    private readonly IConfiguration _configuration;

    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options, IConfiguration configuration)
        : base(options)
    {
        _configuration = configuration;
    }

    public DbSet<Student> Students { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured)
        {
            optionsBuilder.UseSqlServer(_configuration.GetConnectionString("DefaultConnection"));
        }
    }
}

Step 5: Setup Dependency Injection in Program.cs

Configure Dependency Injection and execute LINQ queries.

using System;
using System.Linq;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Configuration;
using System.IO;

class Program
{
    static void Main()
    {
        var serviceProvider = new ServiceCollection()
            .AddSingleton<IConfiguration>(provider =>
            {
                var config = new ConfigurationBuilder()
                    .SetBasePath(Directory.GetCurrentDirectory())
                    .AddJsonFile("appsettings.json")
                    .Build();
                return config;
            })
            .AddDbContext<ApplicationDbContext>()
            .BuildServiceProvider();

        using var context = serviceProvider.GetRequiredService<ApplicationDbContext>();
        context.Database.EnsureCreated();

        InsertSampleData(context);
        PerformLINQQueries(context);
    }

    static void InsertSampleData(ApplicationDbContext context)
    {
        if (!context.Students.Any())
        {
            context.Students.AddRange(
                new Student { Name = "Mani", Age = 22, Grade = "A" },
                new Student { Name = "Pranav", Age = 20, Grade = "B" },
                new Student { Name = "Bhaskar", Age = 21, Grade = "A" },
                new Student { Name = "Vivek", Age = 23, Grade = "C" }
            );

            context.SaveChanges();
        }
    }

    static void PerformLINQQueries(ApplicationDbContext context)
    {
        var student = context.Students.FirstOrDefault(s => s.Name == "Mani");
        Console.WriteLine($"Search Result: {student?.Name} - Age: {student?.Age}, Grade: {student?.Grade}");

        var filteredStudents = context.Students.Where(s => s.Age > 21).ToList();
        Console.WriteLine("Students Older than 21:");
        filteredStudents.ForEach(s => Console.WriteLine($"{s.Name}, Age: {s.Age}"));

        var groupedStudents = context.Students.GroupBy(s => s.Grade)
            .Select(g => new { Grade = g.Key, Count = g.Count() });

        Console.WriteLine("\n Students Grouped by Grade:");
        foreach (var group in groupedStudents)
        {
            Console.WriteLine($"Grade {group.Grade}: {group.Count} students");
        }
    }
}

Step 6: Run Migrations to Create Database

Initialize Migrations

 Add-Migration InitialCreate

Apply Migrations

 Update-Database

Check the git repo

Entity Framework Core

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