EntityManager的使用

您好,请问使用EntityManager创建Query进行查询。Query是否有与数据加载器类似的removeParameter的方法,方便将输入为空的parameter直接remove掉。

   try (Transaction tx = persistence.createTransaction()) {
            // get EntityManager for the current transaction
            EntityManager em = persistence.getEntityManager();
            // create and execute Query
            Query query = em.createQuery(
                    "select sum(o.amount) from sample$Order o where o.customer.id = :customerId");
            query.setParameter("customerId", customerId);
            result = (BigDecimal) query.getFirstResult();
            // commit transaction
            tx.commit();
        }

如上,JPQL 语句里已经包含了参数,不能再remove 掉。可以考虑在拼接查询语句的时候处理。

最近正好写了个类似的:

query = entityManager.createQuery("select o from app_table1" +
            + " o where 1=1"
            + (noDate ? "" : " and o.createTs < :createDate")
            + (noLocation ? "" : " and o.location in :locations")

            + " order by o.createTs");

    if (!noDate) {
        query = query.setParameter("createDate", createDate);
    }
    if (!noLocation) {
        query = query.setParameter("locations", locationList);
    }

    List values = query.getResultList();
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在网上也找到了另一种方式,如下
List list = dataManager.loadValues(“select e.faultReasonName as name,count(e.faultReason) as amount from serviceproject_EventFullProperty e where e.deviceType=:deviceType and (e.eventDate=:startDate or :startDate is null) and (e.eventDate=:endDate or :endDate is null) group by e.faultReason”)
.properties(“name”,“amount”).parameter(“deviceType”,deviceTypeId).parameter(“startDate”,startDate.getValue()).parameter(“endDate”,endDate.getValue()).list();
这里是用datamanager实现的,使用entity manager应该也是一样的

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