Question

一个菜鸟问题，但是为这种情况建立循环的最佳方法是什么？ Suppose I have this table. 我想计算每天创建的记录数，并将每个不同的日期及其记录数存储在数组列表中。如果日期中没有任何记录（例如8/25），则该日期仍应以0计数存储。

数据是从Realm表中提取的，因此SQL查询不起作用。

ArrayList<Date> days = new ArrayList<Date>();
                ArrayList<Integer> recordsPerDay = new ArrayList<Integer>();
                int count = 0;

                for(countresults = 0; countresults <= results.size(); countresults++){
                    if(tblProposalCorporate.getDateCreated()!=lastWeek)
                    {
                        days.add(tblProposalCorporate.getDateCreated());
                        count = 0;
                    }
                    if (tblProposalCorporate.getDateCreated()==lastWeek)
                    {
                        days.add(tblProposalCorporate.getDateCreated());
                        count+=1;
                    }
                }

Answer 1

实际上非常简单，只需从Realm获取最小和最大日期即可。

Date minimumDate = realm.where(Proposal.class).mininumDate("dateCreated");
Date maximumDate = realm.where(Proposal.class).maximumDate("dateCreated");

然后，您可以将这些日期设置为零时，分，秒和毫秒：

Calendar calendar = Calendar.getInstance();
calendar.setTime(minimumDate);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
minimumDate = calendar.getTime();

calendar.setTime(maximumDate);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
maximumDate = calendar.getTime();

现在您要做的就是迭代日期并执行查询以获取数据计数

Map<Date, Long> counts = new LinkedHashMap<>();
for(Date iterDate = new Date(minimumDate); iterDate.getTime() <= maximumDate.getTime(); ) {
    calendar.setTime(iterDate);
    calendar.add(Calendar.DAY_OF_MONTH, 1);
    Date nextDay = calendar.getTime();

    counts.put(iterDate, realm.where(Proposal.class).greaterThanOrEqualTo("dateCreated", iterDate).lowerThan("dateCreated", nextDay).count());

    iterDay.setTime(nextDay.getTime());
}

使用循环来计数Java中每天的记录数

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