Question

Within a c# project I have two collections and I am trying to query them using a lambda to return a value

Pseudo code

Collection1

alertID
SavedItemID
SavedName

Collection2

SavedItemID
alertID
AlertType
DateCreated

var name = Collection2.where(c => c.savedItemID == Collection1.SavedItemID) return SavedName Property value from collection 1.

Basically in the inital query I am hitting collection2 I would like to navigate up from collection2 into collection one to return the Saved Name field. I have never attempted to navigate up through a tree to retrieve another object. Can anyone provide some suggestions on how to build this expression?

Thank you

Answer 1

You’ll need to use Join and then project an anonymous type consisting of the fields you care about.

var result = from c2 in Collection2
    join c1 in Collection1 on c2.SavedItemID equals c1.SavedItemID
    select new { c2.SavedItemID, c1.SavedName };

This is equivalent to

var result = Collection2.Join(
    Collection1, 
    c2 => c2.SavedItemId, 
    c1 => c1.SavedItemId, 
        (c2, c1) => new { c2.SavedItemID, c1.SavedName });