Sunday, April 17, 2011

Linq nuances with WCF Data Service

Don't assume all Linq providers are the same, Linq provider for Entity Framework is different from Linq provider for WCF Data Service

public static IQueryable<T> LimitAndOffset<T>(this IQueryable<T> q,
                    int pageSize, int pageOffset)
    // while this Linq works on both Entity Framework and WCF Data Services...
    // return q.Skip((pageOffset - 1) * pageSize).Take(pageSize);
    // ...this Linq doesn't work on WCF Data Service
    return q.Take(pageSize).Skip((pageOffset - 1) * pageSize);

I answered a colleague that Skip and Take's order doesn't matter (i.e. can call Take then Skip also) because it is deferredly executed, felt a little stupid for naturally assuming it applies to all Linq Providers :-) Linq for WCF Data Services doesn't allow Take then Skip. Don't assume anything when it comes to Linq.

Lesson learned, not all Linq providers are created equal. Lest I forgot, I already encountered one of many Linq's nuances a long time ago, example:

I should have known better :-)

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