Fetch multiple in NPoco when children has its own mapping to do - petapoco

Question

I have been successful with fetching a parent and its children with NPoco FetchManyToOne with this code:
public class Parent
{
public int Id { get; set; }
public string Name { get; set; }
public IList<Child> Children { get; set; }
}
public class Child
{
public int Id { get; set; }
public int ParentId { get; set; }
public string Name { get; set; }
}
db.FetchOneToMany<Parent, Child>(parent => parent.Id, child => child.Id,
#"SELECT
P.Id, P.Name,
C.Id, C.ParentId, C.Name
FROM Parent AS P
LEFT JOIN Child AS C ON P.Id = C.ParentId",
id);
Now there is this scenario when a child can belong to a period. A children does not have to belong to a period as this is optional.
In the database the Period table consists of an id column and two datetime columns, Start and End. The Child table has a new column, PeriodId which can contain a null value if it does not belong to a period.
The class Child now gets a new property of type Period. Which can be null or an instance of class Period.
Look at the changes to the class structures:
public class Parent
{
public int Id { get; set; }
public string Name { get; set; }
public IList<Child> Children { get; set; }
}
public class Child
{
public int Id { get; set; }
public int ParentId { get; set; }
public string Name { get; set; }
public Period ChildPeriod { get; set; }
}
public class Period
{
public int Id { get; set; }
public DateTime Start { get; set; }
public DateTime End { get; set; }
}
How can I map this sql to my classes?
#"SELECT
P.Id, P.Name,
C.Id, C.ParentId, C.Name,
PE.Id, PE.Start, PE.End
FROM Parent AS P
LEFT JOIN Child AS C ON P.Id = C.ParentId
LEFT JOIN Period AS PE ON C.PeriodId = PE.Id"
So that when a child is a part of a period that period is the value of property ChildPeriod on class Child.
Is it possible or do I have to write two calls to the database and do some manual mapping myself?

Answer 1

Since that's really an outer join on Period where Period will sometimes be null, do your Child class as:
public class Child
{
public int Id { get; set; }
public int ParentId { get; set; }
public string Name { get; set; }
[ResultColumn] public DateTime? Start { get; set; }
[ResultColumn] public DateTime? End { get; set; }
}