How to Eager Load Deeply Nested Entities in Entity Framework Core?

Eager Loading Deeply Nested Entities in Entity Framework Core

Background

Eager loading in Entity Framework Core (EF Core) is a technique for pre-fetching related entities along with the primary entity, to avoid multiple database queries. However, in certain scenarios, you may encounter limitations when trying to eager load deeply nested entities.

The Issue

Consider the following scenario:

public class Order
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int CustomerId { get; set; }
    public Customer Customer { get; set; }
}

public class Customer
{
    public int Id { get; set; } 
    public string Name { get; set; }
    public int AddressId { get; set; }
    public Address Address { get; set; }
}

public class Address
{
    public int Id { get; set; }
    public string PostCode { get; set; }
    public string City { get; set; }
}

When you attempt to load an Order with Include(nameof(Customer)).ThenInclude(nameof(Address)), you may notice that the Address property of the Customer entity is null. This occurs because EF Core does not support eager loading of all nested related entities by default.

Proposed Solution

Unfortunately, there is currently no official support for eager loading all deeply nested entities in EF Core. However, there are two custom extension methods you can use to achieve this:

Include Extension:

public static IQueryable<T> Include<T>(this IQueryable<T> source, IEnumerable<string> navigationPropertyPaths)
    where T : class
{
    return navigationPropertyPaths.Aggregate(source, (query, path) => query.Include(path));
}

GetIncludePaths Extension:

public static IEnumerable<string> GetIncludePaths(this DbContext context, Type clrEntityType, int maxDepth = int.MaxValue)
{
    ...
}

Usage Example

In your generic repository, you can modify the GetAllAsync method as follows:

public virtual async Task<IEnumerable<T>> GetAllAsync(Expression<Func<T, bool>> predicate = null)
{
    var query = Context.Set<T>()
        .Include(Context.GetIncludePaths(typeof(T));
    if (predicate != null)
        query = query.Where(predicate);
    return await query.ToListAsync();
}

By using these extension methods, you can eagerly load all nested related entities for the specified type.

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