JPA where子句任何 [英] JPA where clause any
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问题描述
我是JPA的新手。
在JPA中,查询为:
Query query = entityManager.createQuery("select o from Product o WHERE o.category = :value");
query.setParameter("category", category);
如何在JPA中将类别设置为任何类别?因此,如果null类别通过,我会简单地忽略category参数,选择所有产品。
How can I set category to any category in JPA? So if the null category passed, I simple ignore the category parameter, select all products.
推荐答案
如何在JPA中将类别设置为任何类别?因此,如果null类别通过,我简单地忽略category参数,选择所有产品。
How can I set category to any category in JPA? So if the null category passed, I simple ignore the category parameter, select all products.
你必须动态构建查询这里。使用HQL(这是一个简化示例):
You'll have to build the query dynamically here. With HQL (this is a simplified example):
Map<String, Object> params = new HashMap<String, Object>();
StringBuffer hql = new StringBuffer("from Product p");
boolean first = true;
if (category != null) {
hql.append(first ? " where " : " and ");
hql.append("p.category = :category");
params.put("category", category);
}
// And so on...
Query query = session.createQuery(hql.toString());
Iterator<String> iter = params.keySet().iterator();
while (iter.hasNext()) {
String name = iter.next();
Object value = params.get(name);
query.setParameter(name, value);
}
List results = query.list()
但实际上,我的建议是在这里使用Criteria API:
But, actually, my recommendation would be to use the Criteria API here:
Criteria criteria = session.createCriteria(Product.class);
if (category != null) {
criteria.add(Expression.eq("category", category);
}
// And so on...
List results = criteria.list();
对于复杂的动态查询来说简单得多。
Much simpler for complicated dynamic queries.
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