Java 从给定的实体类中截断/删除
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truncate/delete from given the entity class
提问by xenoterracide
I have my entity class available via a method. I'm trying to figure out, how via the JPA JPQL or Criteria API's I could issue a truncate or delete from. I think that the criteria api is more natural for working with classes, and truncate is a faster operation so these are prefered. This is what I put together so far, but not sure what to add/change about it.
我可以通过一种方法使用我的实体类。我想弄清楚，我如何通过 JPA JPQL 或 Criteria API 发出截断或删除。我认为标准 api 更适合处理类，而 truncate 是一种更快的操作，所以这些是首选。到目前为止，这是我整理的内容，但不确定要添加/更改什么。
CriteriaBuilder cb = this._em().getCriteriaBuilder();
cb.createQuery( _entityClass() ).from( _entityClass() );
note: _entityClassreturns MyEntity.class, I have no other references to MyEntitythis is a more generalized implementation.
注意：_entityClass返回MyEntity.class，我没有其他参考，MyEntity这是一个更通用的实现。
采纳答案by wypieprz
Assuming that MyEntityrefers to the table you want to drop you can proceed as follows:
假设MyEntity引用您要删除的表，您可以按以下步骤操作：
// Criteria API (JPA 2.1 and above)
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaDelete<MyEntity> query = builder.createCriteriaDelete(MyEntity.class);
query.from(MyEntity.class);
em.createQuery(query).executeUpdate();
or with a generalized approach:
或使用通用方法：
public <T> int deleteAllEntities(Class<T> entityType) {
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaDelete<T> query = builder.createCriteriaDelete(entityType);
query.from(entityType);
return em.createQuery(query).executeUpdate();
}
Similarly for JPQL/SQL queries:
同样对于 JPQL/SQL 查询：
// JPQL
em.createQuery("DELETE FROM MyEntity e").executeUpdate();
// SQL
em.createNativeQuery("TRUNCATE TABLE MyEntity").executeUpdate();
or with a generalized approach:
或使用通用方法：
public static <T> int deleteAllEntities(Class<T> entityType) {
String query = new StringBuilder("DELETE FROM ")
.append(entityType.getSimpleName())
.append(" e")
.toString();
return em.createQuery(query).executeUpdate();
}
public static <T> int truncateTable(Class<T> entityType) {
String query = new StringBuilder("TRUNCATE TABLE ")
.append(entityType.getSimpleName())
.toString();
return em.createNativeQuery(query).executeUpdate();
}
With Criteria API you can only use SELECT, UPDATE, DELETE statements therefore TRUNCATE is not possible.
使用 Criteria API，您只能使用 SELECT、UPDATE、DELETE 语句，因此 TRUNCATE 是不可能的。
