C#•3y ago

Is Recursive Hierarchy LINQ possible without performance hit or multiple DB calls?

Suppose I have a ToDo Entity that has many sub ToDos. Is it possible to get the whole tree structure without any performance hit?

8 Replies

Angius•3y ago

Yep .Include() or, preferably, .Select()

var blogpost = await _ctx.Blogposts
    .Where(b => b.Id == id)
    .Select(b => new BlogpostDto {
        Title = b.Title,
        Author = b.Author.UserName,
        Tags = b.Tags.Select(t => new TagDto {
            Name = t.Name,
            Color = t.Color
        })
    })
    .FirstOrDefaultAsync();

var blogpost = await _ctx.Blogposts
    .Where(b => b.Id == id)
    .Select(b => new BlogpostDto {
        Title = b.Title,
        Author = b.Author.UserName,
        Tags = b.Tags.Select(t => new TagDto {
            Name = t.Name,
            Color = t.Color
        })
    })
    .FirstOrDefaultAsync();

For example Same goes for recursive Although... with recursive hierarchies you need the .Select() IIRC, using .Include() can lead to some shenanigans

SawaidOP•3y ago

By recursive I mean that I get subtasks of subtasks of subtasks of ...

PontiacGTX•3y ago

you can probably include inner properties if you can loop through them and call Include() ThenInclude() passing an Expression<Func<T,object>>

blinkbat•3y ago

the above example from zzzz does this

SawaidOP•3y ago

but won't the has a hit on performance?

PontiacGTX•3y ago

it will in the time it takes to iterate through each property it is will have a time complexity problem the easiest way to to what you want is probably using an expression and apply a select

SawaidOP•3y ago

How does a recursive select works?

PontiacGTX•3y ago

well i am not sure I supose it select those entities within the select clause internally depending on the navigation property and based on the modelBuilder configuration it uses those mapped entities?

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Is Recursive Hierarchy LINQ possible without performance hit or multiple DB calls?