2. New issues

Compared to dealing with a unidirectional functional association, as discussed in the previous chapter, we have to deal with the following new technical issues:

Comparing Array, Join Table and Parse Relation discussed above, Array is flexible but more complex, there is no exact relation between objects; although Join Table is the classic way to deal with the Many-to-Many relations, it will need to send more requests for a simple purpose; Parse Relation shows its abilities to achieve a better balance between different requests. So we will use Parse Relation in our application.

The last issue, allowing to select a set of associated objects from a list of all existing instances of some class, can, in general, not be solved with the help of an HTML select multiple form element because of usability problems. Whenever the set of selectable options is greater than a certain threshold (defined by the number of options that can be seen on the screen without scrolling), the HTML select multiple element is no longer usable, so we combine an element ul and an element select together.