Introduction
Aggregation operations are actually used for statistical analysis of data. Simply put, they can be understood as aggregation operations in SQL . Aggregation operations in MongoDB are prepared for big data analysis. Here is a brief introduction to the use of the aggregation framework aggregate .
Pipeline Mode Aggregation Analysis
MongoDB 's aggregation framework is implemented with reference to pipeline commands on UNIX . Data passes through a multi-step pipeline, each step processes the data, and finally returns the required result set.
Pipeline aggregation can operate on a fragmented collection ( The aggregation pipeline can operate on a sharded collection. )
Pipeline aggregation can use indexes to improve performance at certain stages. In addition, pipeline aggregation has an internal optimization stage (later pipeline aggregation Optimization will be discussed).
Common pipeline operators are as follows:
| operator |
illustrate |
| $match |
filter documents |
| $limit |
Limit the data of the files in the pipeline |
| $skip |
skip the specified number of documents |
| $sort |
Sort the entered documents |
| $group |
Calculate aggregated results after grouping documents |
| $out |
Output documents to a specific collection (must be the last step of the pipeline operation) |
Aggregation operators used with $ group :
| operator |
illustrate |
| $first |
Returns the first value after group |
| $last |
Returns the last value after group |
| $max |
The maximum value after group |
| $min |
The minimum value after group |
| $avg |
average after group |
| $sum |
sum after group |
Example:
db.Collection.aggregate(
{$match : {"appId" : "2e1800b22ae70600", "leaveTime" : {"$gt" : ISODate("2017-07-12T00:00:00"), "$lt" : ISODate("2017-07-13T00:00:00")}}},
{$group : {"_id" : "$leaveMethod", "count" : {$sum : 1}}},
{$sort : {"_id" : 1}}
)
Integrate into java operation
First import mongodb 's java driver package mongo-java-driver-3.2.2.jar
Use the new Document() object to replace the above {"XXX": "XXX"} condition
Example:
public String aggregateLeaveMethodByDate(String app_id, Date beginDate, Date endDate) throws Exception {
MongoCollection<Document> collection = PluginMongo.instance().getDatabase().getCollection(MongoCollectionName.PARKING_RECORD);
Document sub_match = new Document();
sub_match.put("appId", app_id);
sub_match.put("leaveTime", new Document("$gt", beginDate).append("$lt", endDate));
Document sub_group = new Document();
sub_group.put("_id", "$leaveMethod");
sub_group.put("count", new Document("$sum", 1));
Document match = new Document("$match", sub_match);
Document group = new Document("$group", sub_group);
Document sort = new Document("$sort", new Document("_id", 1));
List<Document> aggregateList = new ArrayList<Document>();
aggregateList.add(match);
aggregateList.add(group);
aggregateList.add(sort);
JSONObject ret_obj = new JSONObject();
AggregateIterable<Document> resultset = collection.aggregate(aggregateList);
MongoCursor<Document> cursor = resultset.iterator();
try {
while(cursor.hasNext()) {
Document item_doc = cursor.next();
int leaveMethod = item_doc.getInteger("_id", 0);
int count = item_doc.getInteger("count", 0);
LeaveMethodEnum leaveMethodVal = LeaveMethodEnum.fromType(leaveMethod);
ret_obj.put(leaveMethodVal.name(), count);
}
} finally {
cursor.close();
}
return ret_obj.toJSONString();
}