hibernate，检查对象是否存在以及null值

Question

I am using hibernate to save records (ie objects) to a database. Before saving my objects, I want to verify if the database already contains this object . (The primary key is just an incremental key and cannot be used for this.)

I am creating a HQL statement at runtime to check the existance of a record with these attributes (ie column1-3 ).

The resulting query should look like:

from myTable where column1 is null and column2 = :column2 and column3 = :column3'

Because sometimes the columns can contain null values , I check the value of the attributes, if it is a NULL value, then I use a is instead of a = in this query (eg the column1 is :column1 in the above statement).

Because I start to realize that I am doing a lot of work to achieve something reletively crucial, I am starting to wonder if I'm on the right track. Is there an easier way to check the existance of objects ?

EDIT: I slightly rephrased my question after I realized that also column1 is :column1 does not work when :column1 parameter is set to null . Apparently the only syntax that seems to work as expected is column1 is null . So, it seems like you just cannot use wildcards when searching for null values. But that does not change the main aspect of my question: should I really be checking all this stuff at runtime ?

Answer 1

This is the best way that I found so far.

I prefer to put my filters in a map. The key refers to the property (ie map.put("column1", Integer.valueOf(1)) ).

There is a Restritions.eqOrIsNull method that simplifies the conversion to a Criterion object. The following method converts an entire Map to a List<Criterion> .

public List<Criterion> mapToCriterion(Map<String, Object> params)
{
  if (params == null) return null;

  // convert the parameter map to a list of criterion
  List<Criterion> criterionList = new ArrayList<>(params.size());
  for (Map.Entry<String, Object> entry : params.entrySet())
    criterionList.add(Restrictions.eqOrIsNull(entry.getKey(), entry.getValue()));
  return criterionList;
}

Later on, I use the List<Criterion> to build a Criteria object.

 Criteria criteria = session.createCriteria(clazz);
 if (criterionList != null)
 {
   for(Criterion criterion : criterionList) 
     criteria.add(criterion);
 }

 // get the full list
 @SuppressWarnings("unchecked")
 List<T> objectList = criteria.list();

My general impression is still that there are missing several convenience methods here (eg Criteria#addAll(List<Criterion>) would have been nice).