Monday, October 26, 2009

PLINQO Query Extension Updates

The Problem

Unfortunately the previous query extensions, while great at querying by a particular value, did not support simple operations such as getting by a nullable value type (where you know it can be null or just a value).

Example: If you want to query by a nullable column, you had to use a a lambda expression.

context.Product.Where(p => !p.OwnerId.HasValue || p.OwnerId.Value == 5);

Our Solution

Add an overload that for each "By" extension method that accepts a params list of values.

Example: Now you can look for null OR a certain value without using where statement.

context.Product.ByOwnerId(null, 5);

New PLINQO Feature

Here at CodeSmith we love generic solutions. So, forget just supporting ByValueOrNull scenarios, now all "By" query extensions have an overload to support or statements!

Example: Ummm, every single "By" query extension method generated by PLINQO?

context.Task.ByPriority(Priority.High, null, Priority.Medium);
context.Person.ByFirstName("Eric", null, "Shannon", String.Empty);
context.Product.ByName("Scribblenauts", "Bowser's Inside Story").ByRating(Rating.Excellent, Rating.AboveAverage);

Implementation Details

To see how the overloads are implemented you need only take a look at the template, QueryExtension.Generated.cst. If you are curious to see how all of this comes together under the hood, where we build up the parametrized query string and then parse the lambda, this code is located in DynamicQuery.cs

Fun Little FYI Facts: Unfortunately Linq to SQL does not support doing a IEnumerable.Contains against a nullable value type collection to identify null values. Also, when building a string expression, you cant just say where a primitive is equal to a null, that will cause a parsing exception. So once we jumped those hurdles, the rest was relatively easy; just check for null params arrays in the overloads and know when to treat them as a null vs an empty param, and you're all set!

In Conclusion

Linq rocks. PLINQO just keeps getting better. Check out our new nightly builds, or wait for PLINQO 3.2, coming soon to our Google Code repository near you!

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