C#•2y ago

✅ (Linq) Assigning value in OrderBy lambda function

   int hrVoteResult = 0;
    comment.highlightedReply = await _mapper.ProjectTo<ReplyDtoRead_2>(_db.Replies
     .Where(r => r.deletedStatus.body == "Default" &&
            r.commentId == comment.id)
    .OrderByDescending(r => 
    {
         hrVoteResult = r.Votes.Sum(v => v.body == true ? 1 : -1;
         return hrVoteResult;
    })
   .Take(1))
   .FirstOrDefaultAsync();

   int hrVoteResult = 0;
    comment.highlightedReply = await _mapper.ProjectTo<ReplyDtoRead_2>(_db.Replies
     .Where(r => r.deletedStatus.body == "Default" &&
            r.commentId == comment.id)
    .OrderByDescending(r => 
    {
         hrVoteResult = r.Votes.Sum(v => v.body == true ? 1 : -1;
         return hrVoteResult;
    })
   .Take(1))
   .FirstOrDefaultAsync();

Error: A lambda expression must have an expression body to be converted to an expression tree. This works fine btw; .OrderByDescending(r => r.Votes.Sum(v => v.body == true ? 1 : -1)

18 Replies

Angius•2y ago

Then do it the way it works ¯\_(ツ)_/¯ The issue is, as it says, expression trees need the lambdas to be expression-bodied

İrşat•2y ago

I need that vote result 😄

Angius•2y ago

.Select() it in a way that also gives it to you

İrşat•2y ago

Alternatively, I have to assign it to "comment.highlightedReply.voteResult

Angius•2y ago

Ah, you're already using automapper to map it to some weirdly-named DTO So you probably can't .Select() it Well, either mess around with the mapper config so you get what you need Or try to make that .Select() work with the mapper Or ditch the mapper here and just .Select()

İrşat•2y ago

I can give the vote result straight from the dto constructor but it's definetely bad practice Btw, why can't I use other codes in lambda function? What does it want as a return?

Angius•2y ago

It wants an expression Because the framework knows how to translate expressions to SQL

İrşat•2y ago

What kind of expression are we talking here? sql query kind of thing?

Angius•2y ago

No, an expression, in the C# sense Something that immediately returns a single value Like, expression-bodied methods

İrşat•2y ago

So, it wants something to turn it into sql so it can fetch stuff. And I am trying to run c# code in it which is a no-no ?

Angius•2y ago

In both cases it's C# code It's just that an expression can easily be parsed and translated And a statement body cannot

İrşat•2y ago

.OrderByDescending(r => 
                    {
                        return r.Votes.Sum(v => v.body == true ? 1 : -1);
                    })

.OrderByDescending(r => 
                    {
                        return r.Votes.Sum(v => v.body == true ? 1 : -1);
                    })

Why doesn't this work then? Isn't this just the same code with extra steps?

Angius•2y ago

But it's not an expression It has a body, denoted by {} And a return

İrşat•2y ago

AI insists that it should work. It has a long way to go it seems

Angius•2y ago

AI is notorious for being confidently incorrect

İrşat•2y ago

As a last resort, I can make it two different queries. One that gets the highlighted reply. Other one gets the vote result by the id of this reply.

comment.highlightedReply = await _mapper.ProjectTo<ReplyDtoRead_2>(_db.Replies
                    .Where(r => r.deletedStatus.body == "Default" &&
                        r.commentId == comment.id)
                    .OrderByDescending(r => r.Votes.Sum(v => v.body == true ? 1 : -1))
                    .Take(1))
                .FirstOrDefaultAsync();
            if(comment.highlightedReply != null){
                comment.highlightedReply.voteResult = _db.Votes
                    .Where(v => v.targetReplyId == comment.highlightedReply.id)
                    .Sum(v => v.body == true ? 1 : -1);
            }

comment.highlightedReply = await _mapper.ProjectTo<ReplyDtoRead_2>(_db.Replies
                    .Where(r => r.deletedStatus.body == "Default" &&
                        r.commentId == comment.id)
                    .OrderByDescending(r => r.Votes.Sum(v => v.body == true ? 1 : -1))
                    .Take(1))
                .FirstOrDefaultAsync();
            if(comment.highlightedReply != null){
                comment.highlightedReply.voteResult = _db.Votes
                    .Where(v => v.targetReplyId == comment.highlightedReply.id)
                    .Sum(v => v.body == true ? 1 : -1);
            }

This should work. I don't know how else if not expression body

Saber•2y ago

This would work in normal linq, but EF has entirely different rules.

İrşat•2y ago

it pains me to make an another query 😄 (I am eating dinner for the next 20 min, sorry if I can't reply)

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✅ (Linq) Assigning value in OrderBy lambda function