Hi all,
I am using for first time the DMF (Data Migration Framework) and I am already building my own Target Entities. I have everything more or less clear but I have some points that I dont fully understand so it would be nice to discuss here with you all 
First. It seems that if you want to use methods in the conversion from staging fields to target entity you need to created field groups in your custom Entity table with the same name of the method you want to use later on the relation diagram or in the mapping details. I find this a little strange and and dont know why we should do that. Also these field groups seems that should have only the field that you want to convert but not sure.
Also I dont have clear how the method getReturnFields on the entity class should be written. For example on the class DMFCustomerEntityClass we have the following code:
case methodStr(DMFCustomerEntityClass, GenerateCompanyIdNAF) :
con += [fieldstrToTargetXML(fieldStr(CustTable, CompanyNAFCode))];
break;
case methodStr(DMFCustomerEntityClass, GeneratePostalAddress) :
break;
Also I dont have clear when we should return the container and when not.