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PODoes "Select New" in linq trigger an evaluation / load?
 

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  1. PODoes "Select New" in linq trigger an evaluation / load?
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    <p>I'm currently trying to create a class which implements <code>IEnumerable&lt;T&gt;</code> in order to construct a Hierarchy from a flat list of objects which have references to each other through a ParentId property. I'd like to write a fluent interface for this so I can do something like this</p> <pre><code>IEnumerable&lt;Tab&gt; tabs = GetTabs(); IEnumerable&lt;TabNode&gt; tabNodes = tabs.AsHierarchy().WithStartLevel(2).WithMaxDepth(5); </code></pre> <p>So, about the yield statement, I wonder whether I could do something like this within my <code>NodeHierarchy : IEnumerable&lt;TabNode&gt;</code> class:</p> <pre><code>private IEnumerable&lt;TabNode&gt; _nodes; public NodeHierarchy(IEnumerable&lt;Tab&gt; tabs) { _nodes = CreateHierarchy(tabs); } public IEnumerable&lt;TabNode&gt; CreateHierarchy(IEnumerable&lt;Tab&gt; tabs) { /* About this block: I'm trying to find the top level nodes of the first tab collection, maybe this is done poorly? */ var tabIds = tabs.Select(t =&gt; t.TabID); IEnumerable&lt;TabNode&gt; nodes = from tab in tabs where !tabIds.Contains(tab.ParentId) select new TabNode { Tab = node, ChildNodes = CreateHierarchy(tabs, node.TabID, 1), Depth = 1 }; return nodes; } </code></pre> <p>or whether I would have to do something like this:</p> <pre><code>private IEnumerable&lt;TabNode&gt; _nodes; public NodeHierarchy(IEnumerable&lt;Tab&gt; tabs) { _nodes = CreateHierarchy(tabs); } public IEnumerable&lt;TabNode&gt; CreateHierarchy(IEnumerable&lt;Tab&gt; tabs) { var tabIds = tabs.Select(t =&gt; t.TabID); IEnumerable&lt;Tab&gt; startingNodes = from tab in tabs where !tabIds.Contains(tab.ParentId) select tab; foreach(Tab node in startingNodes) { yield return new TabNode() { Tab = node, ChildNodes = CreateHierarchy(tabs, node.TabID, 1), Depth = 1 }; } </code></pre>
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    1. USkitsune
    1. USkitsune
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      1. VTUpMod
    1. COCould you reformat your code using spaces instead of tabs? It's pretty unreadable at the moment.
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      1. USJon Skeet
    2. COYeah I know, thanks, I'm working on it... the copy paste job didn't really work here :)
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      1. USkitsune
    3. COShould be fixed now...
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      1. USkitsune
 

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