Select entities with multiple and nested levels without using Include

Question

I have the following entity:

public class Item 
{
    public int Id { get; set; }

    public int? ParentId { get; set; }
    public Item Parent { get; set; }         


        

Answer 1

Let's say we have the following self-referencing table:

public class Person
{
    public Person()
    {
        Childern= new HashSet();
    }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public int? ParentId { get; set; }


    [StringLength(50)]
    public string Name{ get; set; }

    public virtual Person Parent { get; set; }

    public virtual ICollection Children { get; set; }

}

And for some point of time you need to get all grandsons for specific persons.

So, first of all I will create stored procedure(using code-first migration) to get all persons in the hierarchy for those specific persons:

public override void Up()
{
    Sql(@"CREATE TYPE IdsList AS TABLE   
                ( 
                Id Int
                )
                GO

                Create Procedure getChildIds(
                @IdsList dbo.IdsList ReadOnly
                )
                As
                Begin
                WITH RecursiveCTE AS
                (
                    SELECT Id
                    FROM dbo.Persons
                    WHERE ParentId in (Select * from @IdsList)
                    UNION ALL

                    SELECT t.Id
                    FROM dbo.Persons t
                    INNER JOIN RecursiveCTE cte ON t.ParentId = cte.Id
                )
                SELECT Id From RecursiveCTE
                End");
}

public override void Down()
{
    Sql(@" Drop Procedure getChildIds
           Go
           Drop Type IdsList
           ");
}

After that you can use Entity Framework to load the ids(you could modify stored procedure to return persons instead of only returning ids) of persons under the passed persons(ex grandfather) :

 var dataTable = new DataTable();
 dataTable.TableName = "idsList";
 dataTable.Columns.Add("Id", typeof(int));
 //here you add the ids of root persons you would like to get all persons under them
 dataTable.Rows.Add(1);
 dataTable.Rows.Add(2);
//here we are creating the input parameter(which is array of ids)
 SqlParameter idsList = new SqlParameter("idsList", SqlDbType.Structured);
 idsList.TypeName = dataTable.TableName;
 idsList.Value = dataTable;
 //executing stored procedure
 var ids= dbContext.Database.SqlQuery("exec getChildIds @idsList", idsList).ToList();

I hope my answer will help others to load hierarchical data for specific entities using entity framework.