Tag assocation and attribute extends in duplicate records

[moyuking233]

It is utterly confusing to me that using tag assocation and attribute extends . Here is the sql and the result.Basically i just want to select one permission with many roles. Then,I using java class to resolve them. 4 records as expected. So I created a dto to handle the duplicate records with 2 different solutions like this: Solution one -- using assocation mapper.xml java bean reulst: Still return 4 records. Solution two -- using extends attributes mapper.xml java bean result: Return 2 records with List<Role> as expected After using extends attribute, it working fine so far. I was wandering can assocation do this like that?