java 使用 sql 查询在休眠中创建一个新的对象实例
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Creating a new object instance in hibernate using a sql query
提问by stjohnroe
I am attempting to create an object in hibernate using a query, which will then be saved back to the table representing the class.
我正在尝试使用查询在 hibernate 中创建一个对象，然后将其保存回表示该类的表中。
Excerpt from hbm.xml file:
摘自 hbm.xml 文件：
<class name="MyClass" table="MY_TABLE">
<id column="ID" name="ID">
<generator class="sequence">
<param name="sequence">MY_SEQ</param>
</generator>
</id>
<property column="VAL" name="val" type="string"/>
</class>
<sql-query name="myQuery">
<return class="MyClass"/>
SELECT MY_SEQ.nextval ID, 'something' VAL from DUAL
</sql-query>
Code snippet from test case:
测试用例的代码片段：
MyClass myClass = (MyClass) session.getNamedQuery("myQuery").list().get(0);
Transaction t = session.beginTransaction();
session.save(myClass);
t.commit();
My aim is that there should now be a new record in table MY_TABLE, but the insert does not occur, I assume that this is due the fact that Hibernate does not know that the instance has not been persisted in the db.
我的目标是现在表 MY_TABLE 中应该有一个新记录，但不会发生插入，我认为这是由于 Hibernate 不知道该实例尚未保存在数据库中的事实。
I have tried changing the query to read:
我尝试将查询更改为：
SELECT NULL ID, 'something' VAL from DUAL
But this results in Hibernate not instantiating an object.
但这会导致 Hibernate 没有实例化一个对象。
So how can i create a new object instance from a query that is not associated with a persisted instance of the class and use this to create a persisted instance?
那么如何从与类的持久化实例无关的查询创建一个新的对象实例，并使用它来创建一个持久化实例呢？
回答by Pascal Thivent
Update:I tested the approach suggested below and I couldn't get it working for this particular scenario, Hibernate expects you to select columns for all attributes while we definitely don't want the id. However, using a ResultTransformerdid work:
更新：我测试了下面建议的方法，但我无法让它适用于这个特定场景，Hibernate 期望您为所有属性选择列，而我们绝对不想要 id。但是，使用ResultTransformer确实有效：
16.1.5. Returning non-managed entities
It is possible to apply a
ResultTransformerto native SQL queries, allowing it to return non-managed entities.sess.createSQLQuery("SELECT NAME, BIRTHDATE FROM CATS") .setResultTransformer(Transformers.aliasToBean(CatDTO.class))This query specified:
- the SQL query string
- a result transformer
The above query will return a list of CatDTO which has been instantiated and injected the values of NAME and BIRTHNAME into its corresponding properties or fields.
16.1.5. 返回非托管实体
可以将 a
ResultTransformer应用于本机 SQL 查询，允许它返回非托管实体。sess.createSQLQuery("SELECT NAME, BIRTHDATE FROM CATS") .setResultTransformer(Transformers.aliasToBean(CatDTO.class))此查询指定：
- SQL 查询字符串
- 结果转换器
上述查询将返回已实例化的 CatDTO 列表，并将 NAME 和 BIRTHNAME 的值注入到其相应的属性或字段中。
The documentation mentions returning non-managed entities but it also work with an entity (there is no reason it wouldn't work) and I could persistthe transient entity successfully.
文档提到返回非托管实体，但它也可以与实体一起使用（没有理由它不起作用），我可以persist成功地创建临时实体。
See also
也可以看看
I'm leaving the initial answer for clarity sake.
为了清楚起见，我将留下最初的答案。
Maybe the following will help:
也许以下内容会有所帮助：
16.1.2. Entity queries
The above queries were all about returning scalar values, basically returning the "raw" values from the resultset. The following shows how to get entity objects from a native sql query via
addEntity().sess.createSQLQuery("SELECT * FROM CATS").addEntity(Cat.class); sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").addEntity(Cat.class);This query specified:
- the SQL query string
- the entity returned by the query
Assuming that Cat is mapped as a class with the columns ID, NAME and BIRTHDATE the above queries will both return a List where each element is a Cat entity.
If the entity is mapped with a many-to-one to another entity it is required to also return this when performing the native query, otherwise a database specific "column not found" error will occur. The additional columns will automatically be returned when using the * notation, but we prefer to be explicit as in the following example for a many-to-one to a Dog:
sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE, DOG_ID FROM CATS").addEntity(Cat.class);This will allow
cat.getDog()to function properly.
16.1.2. 实体查询
上面的查询都是关于返回标量值，基本上是从结果集中返回“原始”值。下面展示了如何通过
addEntity().sess.createSQLQuery("SELECT * FROM CATS").addEntity(Cat.class); sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").addEntity(Cat.class);此查询指定：
- SQL 查询字符串
- 查询返回的实体
假设 Cat 被映射为具有列 ID、NAME 和 BIRTHDATE 的类，上述查询都将返回一个 List，其中每个元素都是一个 Cat 实体。
如果实体通过多对一映射到另一个实体，则在执行本机查询时也需要返回此信息，否则将发生数据库特定的“未找到列”错误。使用 * 表示法时，额外的列将自动返回，但我们更愿意像以下示例中的多对一到狗一样明确：
sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE, DOG_ID FROM CATS").addEntity(Cat.class);这将允许
cat.getDog()正常运行。
But I don't think you should set the ID if you want to save it and want Hibernate to perform an insert.
但是我认为如果您想保存 ID 并希望 Hibernate 执行插入操作，则不应该设置 ID。
