Grails的一点小笔记

对于一对多：
只要使用了hasMany后，就建立了单向关联。
如果想建立双向关联，需要使用belongsTo。
单向关联是插入和更新级联，双向关联后连删除也级联。

改变级联关系的关键字：
create: Cascades creations of new instances to associations
merge: Merges a detached association
save-update: Cascades only saves and updates to associations
delete: Cascades only deletes to associations
lock: Indicates whether a pessimistic lock should be cascaded to associations
refresh: Cascades refreshes to associations
evict:Cascades evictions (or discards) to associations
all: Cascades all operations to associations
delete-orphan:: Applies to  one-to- many relationships and indicates that if a child is
removed from an association, the child should be automatically deleted

对于一对一：
双向关联时，并不会级联增删改。
为了级联，必须增加belongsTo关键字。