CODEWITHSUNDEEP
linq
Nate Pet
Nate Pet

Reputation: 46322

LINQ Lambda Order in writing the query

I have the following query:

      var query = db.Prog
       .Where (a => a.Prog != "00000" && a.fn != "Koll")
       .Select(a => new  {a.Prog, a.MEfn})
       .OrderByDescending(a => a.MEfn)

The query works fine but wondering if there are general rules on the order in which you write a Lambda linq query. Meaning, .Where comes before .Select, etc.

Can somebody enlighten me on the order in which LINQ needs to be written or best practices.

Upvotes: 2

Views: 114

Answers (3)

devdigital
devdigital

Reputation: 34369

There isn't a best practice on the order in which you write a LINQ query, it will depend on if you want to do your filtering first, or your projection. For example in your case, you are projecting to an anonymous type which doesn't include the 'fn' property which your filter uses, so it wouldn't be available to use in a where clause if your select was first.

A better practice would be to give your properties less cryptic names. Also, 'fn' doesn't follow the PascalCase for property names, and if it's a field then it probably shouldn't be public.

Upvotes: 1

usr-local-ΕΨΗΕΛΩΝ
usr-local-ΕΨΗΕΛΩΝ

Reputation: 26934

Yours can be a good order.

Let's distinguish the case where db points to an SQL DB with a very good LINQ provider and the case db is an in-memory object. I guess it's the first.

In case you are using a LINQ to SQL provider, the statements are evaluated only when you materialize the query into an object, so the SQL optimizer (inside the DB) will take care of ordering of statements.

The vice versa occurs when your statements are run against in-memory collections or to materialized collections coming from LINQ to SQL. In that case they are executed sequentially, so you want to execute first those statements that reduce the number of results in the collection. Where is the best candidate!!!

Upvotes: 1

Gent
Gent

Reputation: 2685

The order that they should be in are completely dependent on the context of what you are doing. So if your OrderBy is simply formatting the data to be friendly to view, put it at the end after you have trimmed your collection, if your looking for the First value of a sorted collection then maybe you would need it before the collection is iterated to get the first.

Upvotes: 0

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