Entity Framework Core - Lazy Loading

Lazy loading is now available on EF Core 2.1 and here is link to the relevant docs:

https://docs.microsoft.com/en-us/ef/core/querying/related-data#lazy-loading

you can instaling this package for enable lazy loading in EF Core 2.1.

Microsoft.EntityFrameworkCore.Proxies

and then set this config in your ef dbContext

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
     => optionsBuilder
           .UseLazyLoadingProxies()
           .UseSqlServer("myConnectionString");

"Notice" this package works only on EF Core 2.1 and above.

So it appears that EF Core does not currently support lazy loading. Its coming but may be a while off.

For now if anyone else comes across this problem and is struggling. Below is a demo of using Eager loading which is what for now you have to use.

Say before you had a person object and that object contained a List of Hats in another table.

Rather than writing

var person = _context.Person.Where(p=> p.id == id).ToList();

person.Hats.Where(h=> h.id == hat).ToList();

You need to write

var person = _context.Person.Include(p=> p.Hats).Where(p=> p.id == id).ToList();

And then person.Hats.Where(h=> h.id == hat).ToList(); will work

If you have multiple Lists - Chain the Includes

var person = _context.Person.Include(p=> p.Hats).Include(p=> p.Tickets)
                            .Include(p=> p.Smiles).Where(p=> p.id == id).ToList();

I kinda get why this method is safer, that your not loading huge data sets that could slow things down. But I hope they get Lazy loading back soon!!!

Caz

For EF Core 2.1 and above,

Install:

 dotnet add package Microsoft.EntityFrameworkCore.Proxies --version 2.2.4 

Then Update your Startup.cs file as indicated below.

using Microsoft.EntityFrameworkCore.Proxies;



services.AddEntityFrameworkProxies();
services.AddDbContext<BlogDbContext>(options =>
            {
                options.UseSqlite(Configuration.GetSection("ConnectionStrings")["DefaultConnection"]);
                options.UseLazyLoadingProxies(true);
            });