C# in Depth

Extension methods in .NET 3.5269Now that we’ve seen how all these apply to our “collection of numbers” example, it’stime for me to make good on the promise of some more business-related situations.10.3.5 Business examples involving chainingMuch of what we do as developers involves moving data around. In fact, for manyapplications that’s the only meaningful thing we do—the user interface, web services,database, and other components often exist solely to get data from one placeto another, or from one form into another. It should be of no surprise that theextension methods we’ve looked at in this section are well suited to many businessproblems. I’ll just give a couple of examples, as I’m sure you’ll be able to take themas a springboard into thinking about your business requirements and how C# 3 andthe Enumerable class can help you solve problems more expressively than before.For each example I’ll only include a sample query—it should be enough to understandthe purpose of the code, but without all the baggage. Full working code is onthe book’s website.AGGREGATION: SUMMING SALARIESThe first example involves a company comprised of several departments. Each departmenthas a number of employees, each of whom has a salary. Suppose we want toreport on total salary cost by department, with the most expensive department first.The query is simplycompany.Departments.Select(dept => new{dept.Name,Cost=dept.Employees.Sum (person => person.Salary)}).OrderByDescending (deptWithCost => deptWithCost.Cost);This query uses an anonymous type to keep the department name (using a projectioninitializer) and the sum of the salaries of all the employees within that department.The salary summation uses a self-explanatory Sum extension method, again part ofEnumerable. In the result, the department name and total salary can be retrieved asproperties. If you wanted the original department reference, you’d just need tochange the anonymous type used in the Select method.GROUPING: COUNTING BUGS ASSIGNED TO DEVELOPERSIf you’re a professional developer, I’m sure you’ve seen many project managementtools giving you different metrics. If you have access to the raw data, LINQ can helpyou transform it in practically any way you choose. As a simple example, we could lookat a list of developers and how many bugs they have assigned to them at the moment:bugs.GroupBy(bug => bug.AssignedTo).Select(list => new { Developer=list.Key, Count=list.Count() }).OrderByDescending (x => x.Count);This query uses the GroupBy extension method, which groups the original collectionby a projection (the developer assigned to fix the bug in this case), resulting in anLicensed to Rhona Hadida