java 如何使用 EclipseLink 在仅具有唯一值的列中查找值？
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How do I find a value in a column that just have unique values with EclipseLink?
提问by Rox
You have the EntityManager.find(Class entityClass, Object primaryKey)method to find a specific row with a primary key.
您可以EntityManager.find(Class entityClass, Object primaryKey)使用主键查找特定行。
But how do I find a value in a column that just have unique values and is not a primary key?
但是如何在只有唯一值而不是主键的列中找到一个值？
采纳答案by maksimov
For example, like this:
例如，像这样：
List<T> results = em.createQuery("SELECT t FROM TABLE t", T.class)
.getResultList();
With parameters:
带参数：
List<T> results = em.createQuery("SELECT t FROM TABLE t where t.value = :value1")
.setParameter("value1", "some value").getResultList();
For single result replace getResultList()with getSingleResult():
对于单个结果替换getResultList()为getSingleResult()：
T entity = em.createQuery("SELECT t FROM TABLE t where t.uniqueKey = :value1")
.setParameter("value1", "KEY1").getSingleResult();
One other way is to use Criteria API.
另一种方法是使用 Criteria API。
回答by Pau Kiat Wee
You can use appropriate JPQL with TypedQuery.
您可以将适当的 JPQL 与TypedQuery一起使用。
try {
TypedQuery<Bean> tq = em.createQuery("from Bean WHERE column=?", Bean.class);
Bean result = tq.setParameter(1, "uniqueKey").getSingleResult();
} catch(NoResultException noresult) {
// if there is no result
} catch(NonUniqueResultException notUnique) {
// if more than one result
}
回答by James
You can use a Query, either JPQL, Criteria, or SQL.
您可以使用查询，JPQL、Criteria 或 SQL。
Not sure if your concern is in obtaining cache hits similar to find(). In EclipseLink 2.4 cache indexes were added to allow you to index non-primary key fields and obtain cache hits from JPQL or Criteria.
不确定您是否关心获取类似于 find() 的缓存命中。在 EclipseLink 2.4 中添加了缓存索引以允许您索引非主键字段并从 JPQL 或 Criteria 获取缓存命中。
See, http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Caching/Indexes
见， http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Caching/Indexes
Prior to 2.4 you could use in-memory queries to query the cache on non-id fields.
在 2.4 之前，您可以使用内存查询来查询非 id 字段的缓存。
