Why relations one-to-many gives me null (Entity framework)? - entity-framework

Question

I have the following application database context:
public class ApplicationContext : DbContext
{
private readonly string _connectionString;
public ApplicationContext(IConfiguration configuration)
{
_connectionString = configuration.GetConnectionString("Recipes");
}
public DbSet<User> Users { get; set; }
public DbSet<Recipe> Recipes { get; set; }
public DbSet<Ingredient> Ingridients { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseNpgsql(_connectionString);
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Ingredient>()
.HasOne(x => x.Recipe)
.WithMany(y => y.Ingredients);
}
}
My business model is simple: one recipe has many ingredients and one ingredient has only one receipt.
Models
Recipe:
public class Recipe
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public List<Ingredient> Ingredients { get; set; }
public DateTime CreatedAt { get; set; }
public DateTime UpdatedAt { get; set; }
public Recipe()
{
CreatedAt = DateTime.UtcNow;
UpdatedAt = DateTime.UtcNow;
}
}
Ingredient
public class Ingredient
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public int ClientId { get; set; }
public string Name { get; set; }
public decimal Count { get; set; }
public string Measure { get; set; }
public int Number { get; set; }
public DateTime CreatedAt { get; set; }
public DateTime UpdatedAt { get; set; }
public Recipe Recipe { get; set; }
public Ingredient()
{
CreatedAt = DateTime.UtcNow;
UpdatedAt = DateTime.UtcNow;
}
}
And here I'm trying to get ingredients collection from a recipe:
List<Recipe> recipes;
recipes = _applicationContext.Recipes.Where(r => r.Category.ClientId == id).ToList();
But ingredients is always null. I don't understand why. Here is the result:
What is wrong?

Answer 1

You need to include the child properties in the query or else you will get null back from them. This is done to keep performance fast with Entity Framework. If all child properties were automatically included, many unnecessary joins could be generated in the sql queries that EF generates which can be a pretty large performance hit (and if that were the case, we would likely have a .Exclude extension method!)
i.e:
List<Recipe> recipes = _applicationContext.Recipes.Include(x => x.Ingredients).Where(r => r.Category.ClientId == id).ToList();

Answer 2

Additional to what #GregH said, you can mark the Ingredients as virtual so they can be lazy loaded.
public class Recipe
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public virtual List<Ingredient> Ingredients { get; set; } // marked as virtual
public DateTime CreatedAt { get; set; }
public DateTime UpdatedAt { get; set; }
public Recipe()
{
CreatedAt = DateTime.UtcNow;
UpdatedAt = DateTime.UtcNow;
}
}
Now you can either eager-load them as described in the accepted answer or lazy-load them like you tried to do it before.

Answer 3

If you want navigation properties to Lazy Load in, I think you need to make them virtual.
public virtual ICollection<Ingredient> Ingredients { get; set; }
Or you could include them in your query so they're fetched at the same time as the recipies.
recipesWithIngredients = _applicationContext.Recipes
.Include(r => r.Ingredients)
.Where(r => r.Category.ClientId == id)
.ToList();