public class Goal
{
    public string Text { get; set; }
    public List<SubGoal> SubGoals { get; set; }
}

public class SubGoal
{
    public string Text { get; set; }
    public List<Practise> Practices { get; set; }
    public List<Measure> Measures { get; set; }
}

public interface IGoalPlannerRepository
{
    IEnumerable<Goal> FindAll();
    Goal Get(int id);
    void Save(Goal goal);
}

CREATE PROCEDURE get_GoalAndAllChildObjects
    @goal_id int
AS
SELECT * FROM goal WHERE goal_id = @goal_id
SELECT * FROM subgoals WHERE goal_id = @goal_id

using (var multi = connection.QueryMultiple("get_GoalAndAllChildObjects", new {goal_id=m_goal_id})) {
    var goal = multi.Read<Goal>();
    var subgoals = multi.Read<SubGoal>();
}