How to change the name of the underlying table and columns for a many-to-many relationship

Description:
I want to map my many-to-many relationship to the existing tables but cannot find how to setup mapping to my table and columns. Is this possible?

Answer:
Many-to-many relationship is implemented via an intermediate type, which has a specific name and properties. Names of the class and its properties are composed from the many-to-many association name and collection property names. Though you cannot change XPO's naming rules, you can change names in metadata of persistent classes. Here is some sample code:

C#
using DevExpress.Xpo;  

public class User : XPObject {  
    ...  
    [Association("Users-Roles", typeof(Role))]  
    public XPCollection Roles { get { return GetCollection(nameof(Roles)); } }  
}  
public class Role : XPObject {  
    ...  
    [Association("Users-Roles", typeof(User))]  
    public XPCollection Users { get { return GetCollection(nameof(Users)); } }  
}  

...  
using DevExpress.Xpo;  
using DevExpress.Xpo.Metadata;  

ReflectionDictionary dictionary = new ReflectionDictionary();  
XpoDefault.DataLayer = ...  
XpoDefault.Dictionary = dictionary;  
XPClassInfo classInfo = dictionary.GetClassInfo(typeof(User));  
XPMemberInfo memberInfo = classInfo.GetMember(nameof(User.Roles));  
memberInfo.IntermediateClass.AddAttribute(new PersistentAttribute("RolesToUsers"));  
memberInfo.IntermediateClass.GetMember(nameof(User.Roles)).AddAttribute(new PersistentAttribute("RoleID"));  
memberInfo.IntermediateClass.GetMember(nameof(Role.Users)).AddAttribute(new PersistentAttribute("UserID"));  
memberInfo.IntermediateClass.KeyProperty.AddAttribute(new PersistentAttribute("ID"));

Visual Basic
Imports DevExpress.Xpo  

Class User  
    Inherits XPObject  
    ...  
    <Association("Users-Roles")> _  
    Public ReadOnly Property Roles As XPCollection(Of Role)  
        Get  
            Return GetCollection(Of Role)(NameOf(Roles))  
        End Get  
    End Property  
End Class  

Class User  
    Inherits XPObject  
    ...  
    <Association("Users-Roles")> _  
    Public ReadOnly Property Users As XPCollection(Of User)  
        Get  
            Return GetCollection(Of User)(NameOf(Users))  
        End Get  
    End Property  
End Class  

...  
Imports DevExpress.Xpo  
Imports DevExpress.Xpo.Metadata  

Dim dictionary As New ReflectionDictionary()  
XpoDefault.DataLayer = ...  
XpoDefault.Dictionary = dictionary  

Dim classInfo As XPClassInfo = dictionary.GetClassInfo(GetType(User))  
Dim memberInfo As XPMemberInfo = classInfo.GetMember(NameOf(User.Roles))  
memberInfo.IntermediateClass.AddAttribute(New PersistentAttribute("RolesToUsers"))  
memberInfo.IntermediateClass.GetMember(NameOf(User.Roles)).AddAttribute(New PersistentAttribute("RoleID"))  
memberInfo.IntermediateClass.GetMember(NameOf(Role.Users)).AddAttribute(New PersistentAttribute("UserID"))  
memberInfo.IntermediateClass.KeyProperty.AddAttribute(New PersistentAttribute("ID"))

Metadata is stored in a dictionary. Each Session has a dictionary by default (for backward compatibility with XPO 1.x). It's recommended that you explicitly create a data layer or a dictionary for the XpoDefault object to make all sessions use one and the same dictionary. In this case, you can patch metadata only once as shown above.
If you only need to change the name of the intermediate table and don't care about columns' names, there is a simpler solution: the UseAssociationNameAsIntermediateTableName property of the Association attribute. If you use it, please make sure that the association name exactly matches the intermediate table name in your database.

C#
using DevExpress.Xpo;  

public class User : XPObject {  
    ...  
    [Association("RolesToUsers", typeof(Role), UseAssociationNameAsIntermediateTableName=true)]  
    public XPCollection Roles { get { return GetCollection("Roles"); } }  
}  
public class Role : XPObject {  
    ...  
    [Association("RolesToUsers", typeof(User), UseAssociationNameAsIntermediateTableName=true)]  
    public XPCollection Users { get { return GetCollection("Users"); } }  
}  

Visual Basic
Imports DevExpress.Xpo  

Class User  
    ...  
    <Association("RolesToUsers", UseAssociationNameAsIntermediateTableName:=True)> _  
    Public ReadOnly Property Roles As XPCollection(Of Role)  
        ...  
    End Property  
End Class  

Class User  
    ...  
    <Association("RolesToUsers", UseAssociationNameAsIntermediateTableName:=True)> _  
    Public ReadOnly Property Users As XPCollection(Of User)  
        ...  
    End Property  
End Class  

See Also:
What is the best solution for mapping a many-to-many relation to an existing database?
How to introduce some properties and logic into my many-to-many relation