Hibernate select 查询具有不同的 where 子句
这可能很简单，但我在谷歌上花了几个小时，但找不到相关的答案。
我正在尝试将以下逻辑放入休眠状态，但我无法弄清楚如何进行。 这是我的设置：Mysql 数据库有 2 个表 T1(ID,C1,C2) 和 T2(column1,column2,column3)。 这就是我想要实现的
results = select ID, from T1 //This will result in multiple rows.
for(eachRow in results )
{
select column1,column2,column3 from T2 where ID=eachRow.ID
//Do some computation like
//Assign value of table "T1" column "C1" to table "T2" column "column1"
column1 = eachRow.C1
}
现在我可以想到使用 Hibernate“from”子句将整个表读取到列表中并迭代它的逻辑。但是，这可能会导致 OutOfMemory 异常。您能否建议 HQL 必须如何？
这就是我所做的
Session session = HibernateSession.getSessionFactory().openSession();
Transaction aTableTx = null;
try {
aTableTx = session.beginTransaction();
_allRows = session.createQuery("from T1").list();
for (Iterator<T1> iterator = _allRows.iterator(); iterator.hasNext();)
{
T1 aRow = iterator.next();
//Here I am planning to run a similar to
//_allRows = session.createQuery("from T2").list();
//Store the result and iterate through the list, but
//it is very inefficient.
}
aTableTx.commit();
This might be quite simple but I have spent hours in Google but couldn't find a relevant answer.
I am trying to put the below logic into hibernate but i am not able to figure out how.
This is my setup: Mysql database with 2 tables T1(ID,C1,C2) and T2(column1,column2,column3).
This is what I want to implement
results = select ID, from T1 //This will result in multiple rows.
for(eachRow in results )
{
select column1,column2,column3 from T2 where ID=eachRow.ID
//Do some computation like
//Assign value of table "T1" column "C1" to table "T2" column "column1"
column1 = eachRow.C1
}
For now I could think of a logic of reading the entire table using the Hibernate "from" clause into a List and iterating through it. However this might cause a OutOfMemory exception. Could you please suggest how the HQL must be?
This is what I did
Session session = HibernateSession.getSessionFactory().openSession();
Transaction aTableTx = null;
try {
aTableTx = session.beginTransaction();
_allRows = session.createQuery("from T1").list();
for (Iterator<T1> iterator = _allRows.iterator(); iterator.hasNext();)
{
T1 aRow = iterator.next();
//Here I am planning to run a similar to
//_allRows = session.createQuery("from T2").list();
//Store the result and iterate through the list, but
//it is very inefficient.
}
aTableTx.commit();
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您可以使用
scroll()（或iterate()）方法而不是list()滚动到查询结果方法。确保定期刷新和清除会话，如 批量更新的hibernate文档。
另外，内部查询至少应该有一个 where 子句，就像您的伪 SQL 查询一样。这两个实体可能应该与 OneToMany 或 OneToOne 列关联，这将完全避免对此内部查询的需要。
我认为最好的办法是阅读 Hibernate 文档。
You can scroll to the results of a query, using the
scroll()(oriterate()) method, rather than thelist()method.Make sure to regularly flush and clear the session, as explained in the hibernate documentation of batch updates.
Also, the inner query should at least have a where clause, as your pseudo-SQL query has one. The two entities should probably be associated with OneToMany or OneToOne column, which would avoid the need for this inner query completely.
I think the best thing to do would be to read the Hibernate documentation.
在 T1 表中迭代时，您可以运行一个包含 where 子句的查询，如下所示：
While Iterating in the T1 table, you can run a query that will have a where clause in it like this: