Question
I can include only related entities.
using (var context = new BloggingContext())
{
// Load all blogs, all related posts
var blogs1 = context.Blogs
.Include(b => b.Posts)
.ToList();
}
However, I don't need entire BlogPost entity. I'm interested only in particular properties, e.g:
using (var context = new BloggingContext())
{
// Load all blogs, all and titles of related posts
var blogs2 = context.Blogs
.Include(b => b.Posts.Select(p => p.Title) //throws runtime exeption
.ToList();
foreach(var blogPost in blogs2.SelectMany(b => b.Posts))
{
Console.Writeline(blogPost.Blog.Id); //I need the object graph
Console.WriteLine(blogPost.Title); //writes title
Console.WriteLine(blogPost.Content); //writes null
}
}
Popular Answer
You either use Include which loads the entire entity, or you project what you need to a .Select:
var blogs2 = context.Blogs
.Select(x => new
{
BlogName = x.BlogName, //whatever
PostTitles = x.Post.Select(y => y.Title).ToArray()
})
.ToList();
Or, you could do something like this:
var blogs2 = context.Blogs
.Select(x => new
{
Blog = x,
PostTitles = x.Post.Select(y => y.Title).ToArray()
})
.ToList();
A Select is always better when you don't need the entire child, as it prevents querying unneeded data.
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