Retourne le type qui doit etre retourné, c-a-d que si l'utilisateur
demande:
- MyObject[] on retourne MyObject
- Collection<MyObject> on retourne MyObject
- Chunk<MyObject> on retourne MyObject
create sql insert value string, support 'in' as object or collection
ex: "insert into mytable (id, myfield) values ${myobject |values('id', 'myfield)}"
return "insert into mytable (id, myfield) values (?