ChildFragment
ChildFragment<P, C> shows the children of a record: give it the parent and the
property holding its children, and it works out the rest.
ChildFragment<Artist, Album> albums = new ChildFragment<>(artist, Artist_.albumList());
cp.add(albums);
albums.column(Album_.title()).label("Album").width(50);
albums.onClick(album -> UIGoto.moveSub(AlbumEditPage.class, "id", album.getId()));
What it does for you
From the parent and the QField alone it:
- checks that the property really is a downward relation to a collection, and says so plainly if it is not;
- works out the child type from the collection's generic type;
- binds itself to the relation, so it shows whatever the parent's collection holds at any moment;
- puts the children in a
DataTable, using the list as an observable list when it is one - which a Hibernate relation is. Adding a child to the parent's collection then adds a row, with the fragment told nothing.
| Method | What it does |
|---|---|
column(QField<C,V>) / column() |
a column, exactly as on a RowRenderer |
setRenderer(RowRenderer<C>) |
replace the whole row renderer |
onClick(ConsumerEx<C>) |
what clicking a child does |
setOnNew(ConsumerEx<C>) |
show an Add button, and be called with a new child that already has its parent set |
setPageSize(int) |
rows per page; ten by default |
getValue() / setValue(List<C>) |
the children, as the binding sees them |
Why it is worth having
The master/detail screen - a record with its lines under it - is the one screen every application writes many times. Written by hand it is a query, a model, a table, a renderer and the code that keeps them in step with the record on screen. This is four lines, and the part that usually goes wrong - the table still showing the previous record's children - cannot happen, because the fragment is bound to the relation rather than filled from it.
The property must be the collection side of a relation (@OneToMany), and
the fragment must be added to the page: like any control, its binding only
works once it is part of the tree.