如何编写linq表达式以根据状态过滤导航属性？

Question

parent category contains a list of sub categories and sub categories contains a list of sub categories. Now I want to fetch all parent categories if its status is true along with subcategories. I want to check the subcategories status also while fetching. My current query is

 db.Categories.Where(x => x.Status)
.Include(x=>x.SubCategories)
. OfType<ParentCategory>().ToList(); 

how to check the status of subcategories in this query??

Answer 1

Try LINQ's SelectMany() method. It is used to flatten nested collections. Instead of using nested for loops, we can do the task in a more 'LINQ' way.

Ex given below -

Master m1 = new Master() { name = "A", lstObj = new List<obj> { new obj { i = 1, s = "C++" }, new obj { i = 1, s = "C#" }, new obj { i = 1, s = "Java" } } };

Master m2 = new Master() { name = "A", lstObj = new List<obj> { new obj { i = 4, s = "PHP" }, new obj { i = 5, s = "Ruby" }, new obj { i = 6, s = "Perl" } } };

List<Master> lstMasters = new List<Master> { m1, m2 };
var result = lstMasters.SelectMany(m => m.lstObj).Where(o => o.s == "PHP");

Just replace the Master class with your own master class.