public void serializeUpdate(QueryMetadata metadata, RelationalPath<?> entity,
            Map<Path<?>, Expression<?>> updates) {
        templates.serializeUpdate(metadata, entity, updates, this);
    }
Return a list of expressions that can be used to uniquely define the query sources

@param joins
@return identifier columns
querydsl-sql/src/main/java/com/querydsl/sql/SQLSerializer.java