Conditional Include() in Entity Framework

Question

I have seen a few answers to similar questions, however I cannot seem to work out how to apply the answer to my issue.

var allposts = _context.Posts
                 


        

Answer 1

You can use this implementation of an extension method (eg.) Include2(). After that, you can call:

_context.Posts.Include2(post => post.Attachments.Where(a => a.OwnerId == 1))

The code above includes only attachments where Attachment.OwnerId == 1.

Answer 2

try this

var allposts = _context.Posts
        .Include(p => p.Comments)
        .Include(a => a.PostAuthor)
        .Where(t => t.PostAuthor.Id == postAuthorId).ToList();

_context.Attachments.Where(o=>o.Owner is Author).ToList();

Answer 3

Assuming "a" being of type "YourType", a conditonal include could be solved by using a method extension, e.g.

public static class QueryableExtensions
{
    public static IQueryable<T> ConditionalInclude<T>(this IQueryable<T> source, bool include) where T : YourType
    {
        if (include)
        {
            return source
                .Include(a => a.Attachments)
                .Include(a => a.Attachments.Owner));
        }

        return source;
    }
}

... then just use this like you are using .Include, e.g.

bool yourCondition;

.ConditionalInclude(yourCondition)

Answer 4

From the link you posted I can confirm that trick works but for one-many (or many-one) relationship only. In this case your Post-Attachment should be one-many relationship, so it's totally applicable. Here is the query you should have:

//this should be disabled temporarily
_context.Configuration.LazyLoadingEnabled = false;
var allposts = _context.Posts.Where(t => t.PostAuthor.Id == postAuthorId)
                       .Select(e => new {
                           e,//for later projection
                           e.Comments,//cache Comments
                           //cache filtered Attachments
                           Attachments = e.Attachments.Where(a => a.Owner is Author),
                           e.PostAuthor//cache PostAuthor
                        })
                       .AsEnumerable()
                       .Select(e => e.e).ToList();

Answer 5

Lambda in Include() may only point to a property:

.Include(a => a.Attachments)
.Include(a => a.Attachments.Owner);

Your condition doesn't makes sense for me because Include() means join and you either do it or not. And not conditionally.

How would you write this in raw SQL?

---

Why not just this:

context.Attachments
       .Where(a => a.Owner.Id == postAuthorId &&
                   a.Owner.Type == authorType);

?

Answer 6

EF Core 5.0 is introducing Filtered Include soon.

var blogs = context.Blogs
    .Include(e => e.Posts.Where(p => p.Title.Contains("Cheese")))
    .ToList();

Reference: https://docs.microsoft.com/en-us/ef/core/what-is-new/ef-core-5.0/whatsnew#filtered-include