在 Java 中使用 EntityManager 返回计数本机查询的结果？
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时间：2020-11-03 04:41:59 来源:igfitidea点击:
Returning result of count native query using EntityManager in Java?
提问by java123999
I have the following SQL Query :
我有以下 SQL Query :
SELECT COUNT(*) FROM DOG where ID = 'SampleId';
I am trying to write this in java:
我正在尝试将其写入java：
public int returnCountOfDogTable(String id){
String sql= "SELECT COUNT(*) FROM DOG WHERE ID =:id";
Query query = persistence.entityManager().createNativeQuery(sql);
query.setParameter("id", id);
List<Integer> resultList = query.getResultList();
int result = resultList.get(0);
return result;
}
However I get this exception:
但是我得到这个例外：
java.lang.ClassCastException: java.math.BigDecimal cannot be cast to java.lang.Integer
How can I solve this?
我该如何解决这个问题？
回答by Dherik
You can also use Numberand call intValue():
您还可以使用Number和调用intValue()：
Query query = entityManager.createNativeQuery("SELECT COUNT(*) FROM DOG WHERE ID =:id");
query.setParameter("id", 1);
int count = ((Number) query.getSingleResult()).intValue();
回答by Boris
Make sense to use Query#getSingleResultmethod:
使用Query#getSingleResult方法有意义：
Query query = entityManager.createNativeQuery("SELECT COUNT(*) FROM DOG WHERE ID =:id");
query.setParameter("id", 1);
int count = ((BigInteger) query.getSingleResult()).intValue();
回答by Shark
Simply try this:
试试这个：
public int returnCountOfDogTable(String id) {
//...
List<BigDecimal> resultList = query.getResultList();
BigDecimal result = resultList.get(0);
return result.toIntValue();
}
