Javadoc
Deals with one to any association conditions. e.g. Song and Album. An
album have many songs, and a song belongs to one album. So if there's an
Album model defined in Song with private modifier, and in Album there's a
List or Set with generic type of Song and declared as private modifier,
they are one2many association. If there's no List or Set defined in
Album, they will become one2one associations. If there's also a Song
model defined in Album with private modifier, maybe the album just have
one song, they are one2one association too.
When it's many2one association, it's easy to just simply add a foreign id
column to the many side model's table. But when it comes to many2many
association, it can not be done without intermediate join table in
database. LitePal assumes that this join table's name is the
concatenation of the two target table names in alphabetical order.