Get records from database only if children have at least one valid record

Question

How do I get all the records from Categories that have at least one Variable EndDate null? (so if all Varibles are end dated, the Category should not be selected)

I have these 3 entities

public class CategoryType
{
        public int CategoryTypeId { get; set; }
        public string? Name { get; set; }
        public virtual ICollection<Category> Categories { get; set; }
}
public class Category
{
        public int CategoryId { get; set; }
        public string? Name { get; set; }
        public DateTime? EndDate { get; set; }
        public int CategoryTypeId { get; set; }
        public virtual CategoryType CategoryType { get; set; }
        public virtual ICollection<Variable> Variables { get; set; }
}
public class Variable
{
        public int VariableId { get; set; }
        public string? Name { get; set; }
        public DateTime? EndDate { get; set; }
        public string Type { get; set; }        
        public int CategoryId { get; set; }
        public virtual Category Category { get; set; }
        public virtual ICollection<SearchFilter> SearchFilters { get; set; } 
}

I have a mapper that gets called from the service GetCategoryTypes

private async Task<List<FilterDataCategoryTypeDTO>> GetCategoryTypes()
{
     List<FilterDataCategoryTypeDTO> result = new();

     var categoryTypeListEntity = await _context.CategoryTypes
                    .OrderBy(o=> o.Name)
                    .ToListAsync();

     var catTypes = categoryTypeListEntity
                    .Select(s => ManualMapper.ConvertFilterDataCategoryTypeEntityToCategoryDTO(s))
                    .ToList();

     return catTypes;
}     

public static DTO.FilterDataCategoryTypeDTO? ConvertFilterDataCategoryTypeEntityToCategoryDTO(Entities.CategoryType entity)
{
      return entity == null ? null : new DTO.FilterDataCategoryTypeDTO
      {
           CategoryTypeId = entity.CategoryTypeId,
           Name = entity.Name,
           Categories = entity.Categories
                .OrderBy(o=> o.Name)
                .Where(c => c.EndDate == null && c.Variables.Where(r => r.CategoryId == c.CategoryId).Count() == 0)
                .Select(s => ConvertFilterDataCategoryEntityToCategoryDTO(s))
                .ToList()
      } 
}

For example CategoryId=24 should not be select because all EndDates are filled, should only return it if at least one row has EndDate NULL

VariableId  Name            CategoryId  EndDate
33          Tweet Id            24  2022-04-15
34          Id                  24  2022-04-15
35          Url                 24  2022-04-15
36          Type                24  2022-04-15
37          Width               24  2022-04-15
38          Height              24  2022-04-15
39          Media Key           24  2022-04-15
40          Preview Image Url   24  2022-04-15

Answer 1

Try below snipped, you probabbly need to use Any() like:

Categories = entity.Categories
             .OrderBy(o => o.Name)
             .Where(c => c.EndDate == null && c.Variables.Any(r => r.CategoryId == c.CategoryId && r.EndDate == Null))
             .ToList()

This will return all Categories that theirs EndDate are null and at leat have one Variable with Null EndDate.

But below query will get all categories that their Variable list at least have one item with EndDate = Null

entity.Categories.OrderBy(o => o.Name)
                 .Where(c => c.Variables.Any(r => r.CategoryId == c.CategoryId && r.EndDate == Null))
                 .ToList()

If your Model relations established correctly then don't need the first partition of sub query like:

  entity.Categories.OrderBy(o => o.Name)
                     .Where(c => c.Variables.Any(r => r.EndDate == Null))
                     .ToList()

Answer 2

Try following. You need a groupby:

    class Program
    {
        static void Main(string[] args)
        {
            Entity entity = new Entity();
            var results = entity.Variable
                .GroupBy(x => x.CategoryId)
                .Where(x => x.Any(y => y.EndDate.ToString().Length == 0))
                .SelectMany(x => x.Select(y => new { VariableId = y.VariableId, Name = y.Name, CategoryId = y.CategoryId, EndDate = y.EndDate }))
                .ToList();
                
 

        }
    }
    public class Entity
    {
        public List<CategoryType> CategoryTypeId { get; set; }
        public List<Category> Category { get; set; }
        public List<Variable> Variable { get; set; }

    }
    public class CategoryType
    {
        public int CategoryTypeId { get; set; }
        public string? Name { get; set; }
        public virtual ICollection<Category> Categories { get; set; }
}
    public class Category
    {
        public int CategoryId { get; set; }
        public string? Name { get; set; }
        public DateTime? EndDate { get; set; }
        public int CategoryTypeId { get; set; }
        public virtual CategoryType CategoryType { get; set; }
        public virtual ICollection<Variable> Variables { get; set; }
}
    public class Variable
    {
        public int VariableId { get; set; }
        public string? Name { get; set; }
        public DateTime? EndDate { get; set; }
        public string Type { get; set; }        
        public int CategoryId { get; set; }
        public virtual Category Category { get; set; }
        public virtual ICollection<SearchFilter> SearchFilters { get; set; } 
    }
    public class SearchFilter
    {
    }