c# mapping oracle-tables master-detail

Question

Oracle

There are two tables Master and Detail, one-to-many related.
There are corresponding DTO classes for them.
Moreover, the Master class has a field containing a list of objects from the Detail table:

public class Master
    {
        public int Id { get; set; }
        public DateTime Date { get; set; }
        public List<Detail> listDetail
    }

    public class Detail
    {
        public string sql_text { get; set; }
    }

I map the contents of tables into objects of these classes.
Everything is clear with Master. I do one selekt on all necessary records of the table Master - I fill objects of class Master.
But in order to fill the list of the child table, you have to call on each record of the Master select from the Detail table (this select may not return a single record, maybe one or several).
Which is time consuming.
How can you optimize?
Now for mapping I use ORMLite.

Answer 1

Is it not an option to make a Left Join in the database and then assemble it into the desired structure in the RAM?

Answer 2

Deliver ODAC it includes EF for oracle.

Answer 3

Option, but thought to find something automatic.