总结我到目前为止通过不同的stackoverflow帖子发现的内容：
Persist
New
a) out of transaction: allowed. persist accomplished the task of saving both Parent and Child in one call.
b) in of transaction: allowed.
detached
a) out of transaction: allowed. will throw exception when trying to flush.
b) in of transaction: not allowed. will throw exception when trying to flush.
existing
a) out of transaction: allowed. will throw exception when trying to flush.
b) in of transaction: not allowed. will throw exception when trying to flush.
saveOrUpdate
new
a) out of transaction: allowed. will save.
b) in or transaction: allowed. will save.
detached
a) out of transaction: allowed. will update.
b) in of transaction: allowed. will update.
existing
a) out of transaction: allowed. will update.
b) in of transaction: allowed. will update.
save
new
a) out of transaction: allowed. will save. Not sure how can it be saved right away without transaction. save does not cascade to the child, i.e., only Parent is saved/inserted in the table.
b) in or transaction: allowed. will save.
detached
a) out of transaction: save() for a detached object will create a new row in the table.
b) in or transaction: not allowed. will throw exception.
existing
a) out of transaction: not sure what will happen.
b) in or transaction: not allowed. will throw exception.
update
new
a) out of transaction: not sure what will happen. should throw exception.
b) in or transaction: not sure what will happen. should throw exception.
detached
a) out of transaction: allowed. will update later during flush.
b) in or transaction: allowed. will update later during flush.
existing
a) out of transaction: allowed. will update later during flush.
b) in or transaction: allowed. will update later during flush.
merge
new
a) out of transaction: not sure what will happen.
b) in or transaction: if there is no persistent instance currently associated with the session, try to load it from the database, or create a new persistent instance.
detached
a) out of transaction: allowed. will update later during flush. return a copy.
b) in or transaction: allowed. will update later during flush. return a copy.
existing
a) out of transaction: allowed. will update later during flush. return a copy.
b) in or transaction: allowed. will update later during flush. return a copy.
对于具有指定标识符的实体：
save（）：它立即返回实体的标识符。由于在调用save之前已将标识符分配给实体，因此不会立即触发insert。它在会话刷新时被触发。
persist（）：与save相同。它还在冲洗时触发插入。
请验证理解是否正确。
Hibernate persist() vs save() method Hibernate saveOrUpdate vs update vs save/persist Hibernate persist vs save What's the advantage of persist() vs save() in Hibernate? http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/objectstate.html
save vs persist - 应在Transaction中调用所有方法
保存返回ID但不坚持。我们不能坚持分离的对象，因为我们可以保存分离的对象。
update vs merge - 应在Transaction中调用所有方法。
当我有分离对象并且我有一个相同主键的持久性对象时，如果我想要保留分离的对象，那么： - a。如果我们在分离对象上使用update，它将通过异常。湾如果我们在分离的对象上使用merge，它会将字段的值复制到持久性对象并在数据库中更新。
如果我们没有分离对象的相同主键的持久性对象，那么我们可以使用update方法使其持久化。
应始终使用更好的合并方法。
得到vs负载
get方法在调用时始终命中数据库，其中load返回代理对象。当我们访问对象的字段时，它将访问数据库。如果我们不需要使用对象字段的数据，我们只需要将该对象传递给另一个对象，然后我们应该使用load而不是get方法。