java - Group by month with criteria in Hibernate

Question

I'm trying to get a report using Criteria and ProjectionList, and I'm pretty new using this through hibernate. So I have this model:

private Long _userId;

 private Category _category;

 private Long _companyId;

 private Double _amount;

 private Date _date;

And I building the query using this:

  public List sumPaymentsByUserCategoryPeriod(Category category, Long userId,Integer period){
  GregorianCalendar from = new GregorianCalendar();
  from.add(Calendar.MONTH, -period);
  List<CategoryAmount> resultDTO= new ArrayList<CategoryAmount>();

  Criteria criteria = getSession().createCriteria(Payment.class);
  criteria.add(Restrictions.eq("_category", category));
  criteria.add(Restrictions.eq("_userId",userId));
  criteria.add(Restrictions.between("_date", from.getTime(), new Date()));

  ProjectionList projectionList = Projections.projectionList();
  projectionList.add(Projections.sum("_amount"));
  projectionList.add(Projections.groupProperty("_date"));
  criteria.setProjection(projectionList);
  return  criteria.list();

 }

Basically this method receive a Category and a userId to filter the payments records and a period, who will indicate how many months from now to back I want to sum. How can I get the sum result grouped by months?

Any help or tip I'll appreciate it!

Answer 1

I found the answer, and its pretty simple. I changed the "groupProperty" in the ProjectionList criteria for this:

projectionList.add(Projections.sqlGroupProjection(
    "month({alias}.DATE) as month, year({alias}.DATE) as year", 
    "month({alias}.DATE), year({alias}.DATE)", 
    new String[]{"month","year"}, 
    new Type[] {Hibernate.DOUBLE}));

Okay. I'll explain the sqlGroupProjection. The first argument is the part of the query after of the "select", for example:

Select [firstPartOfSqlGroupProjection] * boo;

The "{alias}" is the alias that hibernates use in the query to refer to a table.

The second argument of the sqlGroupProjection function is the group by criteria, the third argument is the column names that you'll get from the group by and finally, the type of data you'll use.