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According to this StackOverflow answer:

Linq to Entities - how to filter on child entities

you should be able to filter down the list of related entities in Entity Framework by utilizing a projection, like I've done here:

Company company = _context.Company
.Where(g => g.CompanyId == id)
.Select(comp => new

 group = comp,
 operators = comp.Operator,
 formFamilies = comp.FormFamily.Where(ff => ff.IsActive ?? false)
).AsEnumerable().Select(i => i.group).FirstOrDefault();

To give a quick overview of what I'm trying to obtain here, I'm trying to get a list of all of the active form families associated with this company object, however, whenever I restrict the results in any way, the result set is empty.

• If the line were formFamilies = comp.FormFamily then it returns two results, one active one inactive


• If the line is formFamilies = comp.FormFamily.Where(ff => true) then it returns nothing


• If the line is formFamilies = comp.FormFamily.OrderBy(ff => ff.FormFamilyId) then it returns nothing.

Any sort of modification that I do to comp.FormFamily means the result set returns nothing, I've dug through the deepest sections of SA to try to find a solution, and tried every solution I've found, but nothing seems to cause this list to return anything.

Assuming that Company and FormFamily entities has one to many relationship I would suggest to use a join statement.Something like this should give you what you are looking for.

 var company = from c in _context.Company
 join f in _context.FormFamily
 on c.Id equals f.CompanyId 
 where c.Id == id
 select new Company()
 
 Id = c.Id,
 operators = c.Operator.ToList(),
 formFamilies = c.FormFamily.Where(x=>x.IsActive == 
 false).ToList()
 .FirstOrDefault();

Hope this helps.

I didn't quite understand what is your query is supposed to do. But it seems to me that you cannot just call Select method on another Select result method.

Anyway, you could simply use Include methods instead of projecting.

var company = _context.Company
 .Where(c => c.Id == id)
 .Include(c => c.FormFamily).Where(ff => ff.IsActive ?? false)
 .ToList();

Did not test it. To prove it works or not be sure put an entity model in the question. Then I may produce more accurate answer.