I have this code. How can I check for null values with the SingleOrDefault method?
public static List<ETY.Rol> GetRolesByApplicationAndCompany(this UsuarioContext usuario, int company, int app)
{
List<ETY.Company> lCompanies= usuario.Companies;
var roles = lCompanies.
SingleOrDefault(e => (e.Id == company)).Applications.
SingleOrDefault(a => a.Id == app).Roles;
return roles;
}
You could try looking at a Maybe/IfNotNull extension method (here and here).
Or use Linq syntax something like this (untested):
var q = from company in lCompanies.SingleOrDefault(e => e.Id == company)
where company != null
let application = company.Applications.SingleOrDefault(a => a.Id == app)
where application != null
select application.Roles;
(Greg Beech's answer is better if the Single condition is guaranteed)
Do you mean returning null or an empty list if any of the SingleOrDefault returns null? In that case:
var company = lCompanies.SingleOrDefault(e => (e.Id == company));
if(company != null) {
var application = company.Applications.SingleOrDefault(a => a.Id == app);
if(application!=null) {
return application.Roles;
}
}
return null; //Or: return new List<ETY.Rol>();
Rather than using SingleOrDefault you could write a chained query as follows. You lose the semantics of ensuring that there's only a single application or company, but if you know that to always be the case then it shouldn't be a problem.
return from c in lCompanies where c.Id == company
from a in c.Applications where a.Id == app
select a.Roles;