Question

I have the following class objects:

    public class VacancyCategory {     public int ID { get; set; }     public string Text { get; set; }     public IList<VacancySubCategory> SubCategories { get; set; } }      public class VacancySubCategory {     public int ID { get; set; }     public string Text { get; set; }     public VacancyCategory Category { get; set; }     public IList<Vacancy> Vacancies { get; set; } }      public class Vacancy : IBusinessObject {     public int ID { get; set; }     public string Title { get; set; }     public VacancySubCategory SubCategory { get; set; }     public string Body { get; set; }     public VacancyWorkType WorkType { get; set; }     public string Salary { get; set; }     public DateTime? AppsClosingDate { get; set; }     public bool Active { get; set; } } 

…so in a test repository im creating test data like so:

        private IList<VacancyCategory> GetVacancyCategoriesWithAllChildCollections()     {         IList<VacancyCategory> vacancyCategories = new List<VacancyCategory>();          int cCounter = 0;         int scCounter = 0;         int vCounter = 0;         for (int i = 1; i <= 3; i++)         {             VacancyCategory vc = new VacancyCategory();             vc.ID = ++cCounter;             vc.Text = 'VacancyCategory' + i.ToString();              for (int j = 1; j <= 3; j++)             {                 VacancySubCategory vsc = new VacancySubCategory();                 vsc.ID = ++scCounter;                 vsc.Text = 'VacancySubCategory' + scCounter.ToString();                 vsc.Category = vc;                  for (int k = 1; k <= 2; k++)                 {                     Vacancy v = new Vacancy();                     v.ID = ++vCounter;                     v.Title = 'Vacancy' + vCounter.ToString();                     v.Body = 'VacancyBody' + vCounter.ToString();                     v.Active = vCounter >= 16 ? false : true;                     v.WorkType = this._workTypes.Single(wt => wt.ID == k);                     v.Salary = vCounter <= 7 ? 'SR ' + (vCounter * 1000).ToString() : '';                     v.AppsClosingDate = (vCounter >= 3 & vCounter <= 13) ? (new DateTime(2009, 3, vCounter)) : (DateTime?)null;                     v.SubCategory = vsc;                      if (vsc.Vacancies == null)                         vsc.Vacancies = new List<Vacancy>();                     vsc.Vacancies.Add(v);                 }                  if (vc.SubCategories == null)                     vc.SubCategories = new List<VacancySubCategory>();                 vc.SubCategories.Add(vsc);             }              vacancyCategories.Add(vc);         }          return vacancyCategories;     } 

..so now i have some good test data. the object tree / chained objects are important to me.

so i’d like to return the individual object collections from this tree when desired. for example, if i wanted the whole tree, i can just return the VacancyCategory list with all the child objects – great. but now i want to return just the VacancySubCaregory items (all 9 of them). this would be my public method to the test repository:

        public IQueryable<VacancySubCategory> GetVacancySubCategories()     {           throw new NotImplementedException('write gen code');     } 

.. obviously without the exception. i have a member field called _categories that contains the results from the GetVacancyCategoriesWithAllChildCollections method. so i’ve been trying stuff like

this._categories.Select( ...... 

..but i cant seem to return a list of VacancySubCategory objects. i seem to always be selecting the root collection (ie. a result set of VacancyCategory objects). What am i doing wrong? im sure its simple… but its driving me nuts!

EDIT

thanx matt.

your suggestion led me to this:

        public IQueryable<VacancySubCategory> GetVacancySubCategories()     {         return this._categories.SelectMany(c => c.SubCategories).AsQueryable<VacancySubCategory>();     } 

..which works great. you’re a champ

Answer 1

Try:

return this._categories.SelectMany(c => c.SubCategories);