Ef-Core

Previously there was no simple solution for left or right join. We had to use DefaultIfEmpty or GroupJoin and SelectMany.

With DefaultIfEmpty():

var customerOrders = await (
    from c in ctx.Customers
    join o in ctx.Orders on c.CustomerId equals o.CustomerId into orders
    from o in orders.DefaultIfEmpty()
    select new {
        c.CustomerId,
        c.CustomerName,
        OrderId = o == null ? 0 : o.OrderId
    }
).ToListAsync();

I have used the way described above in most of my career. It was really hard to remember that syntax and I always struggled with that.

💻Source code

Lazy loading

You load related entities on demand rather loading at once. This approach is usually useful when you want to load related entities on a certain condition (otherwise always use eager loading).

To enable lazy loading, you need to install this package: Microsoft.EntityFrameworkCore.Proxies

And do following changes in Program.cs

builder.Services.AddDbContext<AppDbContext>(o=>o.UseLazyLoadingProxies()
.UseSqlite("Data Source = mydb.db"));

Look at the example below:

app.MapGet("/", async (AppDbContext context) => {
    foreach (var genre in await context.Genres.ToListAsync()) 
    {
        foreach (var book in genre.Books)
        {
            Console.WriteLine($"===> genre: {genre.Name}, Book: {book.Title}, Price : {book.Author}");
        }
    }
    return Results.Ok("Ok");
});

We are not loading books with genres at once. Rather we are loading books for each genres. Let’s take a look at logs of console.

I have used database first approach in the .NET Framework 4.X. But It is the first time I am trying to use Db First approach in the .NET Core (I am using .net 9). Microsoft refers it ‘Scaffolding (Reverse Engineering)’. Personally I prefer Dapper for DB First approach. May be you have an existing database and you want to use it with ENTITY FRAMEWORK, then this approach might be helpful. I am playing around it and documenting it and sharing that journey with you. Let’s see what it offers.