ASP.NET Web API HTTP GET with optional parameters

Question

Writing my first ASP.NET Web API web service. Still learing the power of Linq as well. I feel like there is a more ideomatic way of doing this:

public class StylesController : ApiController
{
 private Entities db = new Entities();
 // GET api/Styles
 public IEnumerable<Style> GetStyles(int division = 0, int family = 0, int model = 0, int year = 0, string market = "ANY")
 {
 market = market.ToUpper(); // make sure market is upper case
 IEnumerable<Style> q = db.Styles;
 if (division > 0) { q = q.Where(s => s.DivisionId == division); }
 if (family > 0) { q = q.Where(s => s.FamilyId == family); }
 if (model > 0) { q = q.Where(s => s.ModelId == model); }
 if (year > 0) { q = q.Where(s => s.Year == year); }
 if (market != "ANY") { q = q.Where(s => s.MarketCode == market); }
 return q.Distinct().OrderBy(s => s.Id).ToList();
 }
}

• Jeff Vanzella: From what I can see of this code, you are doing an AND operation. i.e. division = 1 AND year = 2012. Am I correct?
• bejumi: Correct, but each part of the AND is optional.
• Turnkey: Fine to return an IEnumerable but that first declaration should be IQueryable<Style> q =

Answer 1

Good layout and white space.

Although the logic works, I think it is very confusing, and not overly obvious. At first glance, it the if statements are very confusing. I would also rename the variables to have an Id or Code to the end of them to keep naming consistent.

I think this is a good place where you could incorporate the Specification Pattern.

public class StylesController : ApiController
{
 private Entities db = new Entities();
 public IEnumerable<Style> GetStyles(int divisionId = 0, int familyId = 0, int modelId = 0, int year = 0, string marketCode = "ANY")
 {
 var divisionIsAMatch = new DivisionIsAMatchSpecification(divisionId);
 var familyIsAMatch = new FamilyIsAMatchSpecification(familyId);
 var modelIsAMatch = new ModelIsAMatchSpecification(modelId);
 var yearIsAMatch = new YearIsAMatchSpecification(year);
 var marketIsAMatch = new MarketIsAMatchSpecification(marketCode);
 var q = db.Styles
 return q.Where(
 divisionIsAMatch
 .And(familyIsAMatch)
 .And(modelIsAMatch)
 .And(yearIsAMatch)
 .And(marketIsAMatch).IsSatisfiedBy
 ).Distinct()
 .OrderBy(s => s.Id);
 }
}

Where

internal class DivisionIsAMatchSpecification : Specification<Style>
{
 private readonly int _divisionId;
 public DivisionIsAMatchSpecification(int divisionId)
 {
 _divisionId = divisionId;
 }
 public bool IsSatisfiedBy(Style style)
 {
 if (_divisionId == 0) 
 {
 return true;
 }
 return style.DivisionId == _divisionId;
 }
}

Just rinse and repeat for each of the specifications you need. Of course, you will have to create the base classes for them too.

I haven't tested this, but I have used this pattern before, and it works really nicely.

• MarkusSchaber: I know it's an old answer, but I'm not happy with this approach. I'm not sure how that should be translated to database statements using LINQ.