Hibernate

hibernate implements limit effect

• Since the limit grammar cannot be written directly in the hql statement, this effect needs to be achieved in other ways.
• limit effects generally require two parameters: start location and number of queries num. Both parameters are final int
• The implementation code is as follows:

try {
            //First, create a final hql statement
            final String hql="from xxb where xx="+xx+" order by xx asc ";
            //hibernate performs a lookup with the parameter of the request return method
            List<xx> xxList=getHibernateTemplate().executeFind(new HibernateCallback() {
                public Object doInHibernate(Session session){
                    //Create a lookup object, set the starting location and the number of queries
                    Query query=session.createQuery(hql);
                    query.setFirstResult(start);
                    query.setMaxResults(num);
                    //Convert to list form
                    return query.list();
                }
            });
            return xxList;
        }catch (RuntimeException e){
            throw  e;
        }

• For the two related methods in the implementation process, the source code can be intercepted and pasted below, or can be viewed by oneself.
  • The executeFind method is implemented as follows:

  public List executeFind(HibernateCallback<?> action) throws DataAccessException { 
        Object result = this.doExecute(action, false, false);
        if (result != null && !(result instanceof List)) {
            throw new InvalidDataAccessApiUsageException("Result object returned from HibernateCallback isn't a List: [" + result + "]");
        } else {
            return (List)result;
        }
    }

  • The doInHibernate method is implemented as follows:

    public List<T> doInHibernate(Session session) throws HibernateException, SQLException {
        Query query = session.createQuery(this.hql).setFirstResult(this.pageModel.getBeginIndex()).setMaxResults(this.pageModel.getPageSize());
        if (!CollectionUtil.listIsNull(this.params)) {
            for(int i = 0; i < this.params.size(); ++i) {
                Object obj = this.params.get(i);
                if (obj instanceof String) {
                    query.setString(i, (String)obj);
                } else if (obj instanceof Integer) {
                    query.setInteger(i, (Integer)obj);
                } else if (obj instanceof Date) {
                    query.setDate(i, (Date)obj);
                }
            }
        }
  
        List<T> list = query.list();
        String counthql = "select count(*) " + this.hql;
        Query countQuery = session.createQuery(counthql);
        if (!CollectionUtil.listIsNull(this.params)) {
            for(int i = 0; i < this.params.size(); ++i) {
                Object obj = this.params.get(i);
                if (obj instanceof String) {
                    countQuery.setString(i, (String)obj);
                } else if (obj instanceof Integer) {
                    countQuery.setInteger(i, (Integer)obj);
                } else if (obj instanceof Date) {
                    countQuery.setDate(i, (Date)obj);
                }
            }
        }
  
        List<Object> countList = countQuery.list();
        if (CollectionUtil.listIsNull(countList)) {
            this.pageModel.setTotalCount(0L);
        } else {
            this.pageModel.setTotalCount((Long)countList.get(0));
        }
  
        return list;
    }