Implement the MongoDB Group function in Java

In non-relational database MongoDB, there is no ready-made framework that can easily implement database grouping through Group By like SQL. If we want to implement the MongoDB Group function, we must write the original NO-SQL query statement to achieve the Group function, which is time-consuming and laborious, and easy to error, this article provides an encapsulated interface to implement the MongoDB Group function, so that programmers no longer worry about the MongoDB Group.

The interface method is as follows:
/**
* KeyColumn: new String [] {"xxxName", "xxxType"} <br>
* Condition: Query condition, which can be null <br>
* Initial: Group counts the initial variables. If it is null, the initial variables are automatically provided for each column. <br>
* Reduce: record processing function <br>
* Finalize: finalize function, which can be empty <br>
*/
Public BasicDBList group (String [] keyColumn, DBObject condition,
DBObject initial, String reduce, String finalize ){
DBCollection coll = getCollection ();
DBObject key = new BasicDBObject ();
For (int I = 0; I <keyColumn. length; I ++ ){
Key. put (keyColumn [I], true );
}
Condition = (condition = null )? New BasicDBObject (): condition;
If (StringUtils. isEmpty (finalize )){
Finalize = null;
}
If (initial = null) {// defines some initial variables
Initial = new BasicDBObject ();
For (int I = 0; I <keyColumn. length; I ++ ){
DBObject index = new BasicDBObject ();
Index. put ("count", 0 );
Index. put ("sum", 0 );
Index. put ("max", 0 );
Index. put ("min", 0 );
Index. put ("avg", 0 );
Index. put ("self ","");
Initial. put (keyColumn [I], index );
}
}
BasicDBList resultList = (BasicDBList) coll. group (key, condition,
Initial, reduce, finalize );
Return resultList;
}

 

Implementation case:

// Task statistics
@ Action (value = "getTaskStatistic", results = {@ Result (name = "success", type = "json", params = {
"IncludeProperties", "jsonResult "})})
Public String getTaskStatistic (){
DBObject initial = new BasicDBObject ();
DBObject index = new BasicDBObject ();
Index. put ("count", 0 );
Index. put ("taskStatus ","");
Initial. put ("taskStatus", index );

String reduce = "function (doc, out ){"
+ "Out. taskStatus. count = out. taskStatus. count + = 1 ;"
+ "Out. taskStatus. inspectStatus = doc. taskStatus ;"
+ "}";
BasicDBList group = (BasicDBList) taskStatusService. group (new String [] {"taskStatus"}, null, initial, reduce, null );

This. jsonResult = group. toString ();
Return SUCCESS;
}

Returned data:
[{"TaskStatus": {"count": 4.0, "taskStatus": "Finished" }}, {"taskStatus": {"count": 3.0, "taskStatus ": "Received" }},{ "taskStatus": {"count": 2.0, "taskStatus": "UnReceive"}]

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