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Welcome! If you’re transitioning from Java to C#, understanding how to work with data is crucial. In this post, we’ll cover Entity Framework Core and ADO.NET for data access in C#. We’ll use real-world examples and draw parallels to Java for a smoother learning experience.

1. Entity Framework Core

Entity Framework Core (EF Core) is an Object-Relational Mapper (ORM) for C#. It simplifies database interactions by allowing you to work with data as objects. This is similar to Java’s Hibernate.

ORM Basics

An ORM helps map database tables to C# classes. For instance, a Customer class might map to a Customers table in your database. EF Core automatically handles the CRUD (Create, Read, Update, Delete) operations for you.

Code-First and Database-First Approaches

1. Code-First Approach: You define your classes first, and EF Core generates the database schema.
   Example Code:
   
   public class Customer
   {
   public int Id { get; set; }
   public string Name { get; set; }
   public string Email { get; set; }
   }
   
   public class AppDbContext : DbContext
   {
   public DbSet<Customer> Customers { get; set; }
   
   protected override void OnConfiguring(DbContextOptionsBuilder options)
   {
   options.UseSqlServer(“your_connection_string_here”);
   }
   }
   
   To create the database, you use Entity Framework migrations:
   
   dotnet ef migrations add InitialCreate
dotnet ef database update
   
2. Database-First Approach: You start with an existing database, and EF Core generates the classes based on the database schema.
   
   Using Database-First:
   dotnet ef dbcontext scaffold "your_connection_string_here" Microsoft.EntityFrameworkCore.SqlServer
   
   This command generates context and entity classes based on your existing database.

LINQ to Entities

LINQ (Language Integrated Query) is used to query data from the database in a readable format. It’s similar to using Streams in Java.

Example Code:

using (var context = new AppDbContext())
{
    var customers = from c in context.Customers
                    where c.Name.Contains("Alice")
                    select c;

    foreach (var customer in customers)
    {
        Console.WriteLine($"{customer.Id}: {customer.Name}");
    }
}

2. Data Access with ADO.NET

ADO.NET provides a more direct way to interact with the database. It gives you control over database operations, similar to Java’s JDBC.

Connecting to Databases

You establish a connection to the database using SqlConnection in C#.

Example Code:

using System.Data.SqlClient;

string connectionString = "your_connection_string_here";
using (SqlConnection connection = new SqlConnection(connectionString))
{
    connection.Open();
    Console.WriteLine("Connection Opened");
}

Executing Queries

You can execute SQL queries and commands directly using ADO.NET.

Example Code:

using System.Data.SqlClient;

string query = "SELECT * FROM Customers";
using (SqlConnection connection = new SqlConnection("your_connection_string_here"))
{
    SqlCommand command = new SqlCommand(query, connection);
    connection.Open();
    SqlDataReader reader = command.ExecuteReader();

    while (reader.Read())
    {
        Console.WriteLine($"{reader["Id"]}: {reader["Name"]}");
    }
}

Data Readers and Data Adapters

• Data Reader: Provides a forward-only stream of data from the database. It’s similar to Java’s ResultSet.
  Example Code:
  using (SqlConnection connection = new SqlConnection(“your_connection_string_here”))
  {
  SqlCommand command = new SqlCommand(“SELECT * FROM Customers”, connection);
  connection.Open();
  SqlDataReader reader = command.ExecuteReader();
  
  while (reader.Read())
  {
  Console.WriteLine($”{reader[“Id”]}: {reader[“Name”]}”);
  }
  }
  
• Data Adapter: Fills a DataSet or DataTable with data from the database. It’s similar to Java’s ResultSet but allows for more complex operations and updates.
  Example Code:
  using System.Data;
  using System.Data.SqlClient;
  string query = “SELECT * FROM Customers”;
  using (SqlConnection connection = new SqlConnection(“your_connection_string_here”))
  {
  SqlDataAdapter adapter = new SqlDataAdapter(query, connection);
  DataTable table = new DataTable();
  adapter.Fill(table);
  foreach (DataRow row in table.Rows) { Console.WriteLine($"{row["Id"]}: {row["Name"]}"); }
  }

This guide should help you get started with data access in C# using Entity Framework Core and ADO.NET. By leveraging your Java knowledge, you can see how these concepts translate into the C# world. Happy coding!