nPoco V3 - many to many not working - many-to-many

Question

I have users which have many roles
public class User
{
public int Id {get;set;}
public string Name {get;set;}
public List<Role> Roles {get;set;}
}
public class Roles
{
public int Id {get;set;}
public string Key{get;set;}
}
public class UserRoles
{
public int UserId {get;set;}
public int RoleId {get;set;}
}
what I try to achieve is getting a user with all its roles in one query, but so far I failed.
For Mapping I use a custom Conventionbased mapper (I can provide the code, but it's rather big)
I tried FetchOneToMany and I tried Fetch as described here
https://github.com/schotime/NPoco/wiki/One-to-Many-Query-Helpers
https://github.com/schotime/NPoco/wiki/Version-3
But Roles is always empty.
Role and User by itself are mapped correctly and I did try to specify the relation like
For<User>().Columns(x =>
{
x.Many(c => c.Roles);
x.Column(c => c.Roles).ComplexMapping();
}, true);
Again it didn't help, roles is empty.
I have no idea what I'm missing.
Any ideas?

Answer 1

ComplexMapping and relationship mapping(1-to-n, n-to-n) are two different things.
ComplexMapping is for mapping nested objects for data that usually resides in the same table where there is a one-to-one relationship. For something like this:
public class Client
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Address Address { get; set; }
public Client()
{
Address = new Address();
}
}
public class Address
{
public string Street { get; set; }
public string City { get; set; }
public string PostalCode { get; set; }
public string Telephone { get; set; }
public string Country{ get; set; }
}
If you're using a convention-based mapper your override would look something like this:
For<Client>().Columns(x =>
{
x.Column(y => y.Address).ComplexMapping();
});
One thing to watch for when using a convention-based mapper; you have to enable ComplexMapping in your scanner with the following code:
scanner.Columns.ComplexPropertiesWhere(y => ColumnInfo.FromMemberInfo(y).ComplexMapping);
Otherwise ComplexMapping() calls in your overrides will simply be ignored.
One-to-Many mapping would work like this (see NPoco on Github for more):
For<One>()
.TableName("Ones")
.PrimaryKey(x => x.OneId)
.Columns(x =>
{
x.Column(y => y.OneId);
x.Column(y => y.Name);
x.Many(y => y.Items).WithName("OneId").Reference(y => y.OneId);
}, true);
For<Many>()
.TableName("Manys")
.PrimaryKey(x => x.ManyId)
.Columns(x =>
{
x.Column(y => y.ManyId);
x.Column(y => y.Value);
x.Column(y => y.Currency);
x.Column(y => y.OneId);
x.Column(y => y.One).WithName("OneId").Reference(y => y.OneId, ReferenceType.OneToOne);
}, true);