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What's the hardest or most misunderstood aspect of LINQ?

Asked 2008-10-18T20:47:40.003
282

Background: Over the next month, I'll be giving three talks about or at least including LINQ in the context of C#. I'd like to know which topics are worth giving a fair amount of attention to, based on what people may find hard to understand, or what they may have a mistaken impression of. I won't be specifically talking about LINQ to SQL or the Entity Framework except as examples of how queries can be executed remotely using expression trees (and usually IQueryable).

So, what have you found hard about LINQ? What have you seen in terms of misunderstandings? Examples might be any of the following, but please don't limit yourself!

  • How the C# compiler treats query expressions
  • Lambda expressions
  • Expression trees
  • Extension methods
  • Anonymous types
  • IQueryable
  • Deferred vs immediate execution
  • Streaming vs buffered execution (e.g. OrderBy is deferred but buffered)
  • Implicitly typed local variables
  • Reading complex generic signatures (e.g. Enumerable.Join)
c# linq c#-3.0
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3 Answers

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In LINQ to SQL I constantly see people not understanding the DataContext, how it can be used and how it should be used. Too many people don't see the DataContext for what it is, a Unit of Work object, not a persistant object.

I've seen plenty of times where people are trying to singleton a DataContext/ session it/ etc rather than making a new time for each operation.

And then there's disposing of the DataContext before the IQueryable has been evaluated but that's more of a prople with people not understanding IQueryable than the DataContext.

The other concept I see a lot of confusion with is Query Syntax vs Expression Syntax. I will use which ever is the easiest at that point, often sticking with Expression Syntax. A lot of people still don't realise that they will produce the same thing in the end, Query is compiled into Expression after all.

answered 2008-10-19T00:05:38.980
1

I find it a bit disappointing that the query expression syntax only supports a subset of the LINQ functionality, so you cannot avoid chaining extension methods every now and then. E.g. the Distinct method cannot be called using the query expression syntax. To use the Distinct method you need to call the extension method. On the other hand the query expression syntax is very handy in many cases, so you don't want to skip that either.

A talk on LINQ could include some practical guidelines for when to prefer one syntax over the other and how to mix them.

answered 2008-12-09T20:01:52.400
1

I have found hard to find clear information about Anonymous types specially in regard of performances in web application. Also I would suggest better and practical Lamda expressions examples and "How to" section in quering and performance related topics.

Hope my brief list can help!

answered 2011-04-27T13:44:50.753

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