creating dynamically group query in java

Question

I have the following database:

  { stream :{ "name": "name1",
       "error1": 1,
       "error2": 1,
       "error3": 1 }
  }

,

{ stream : {"name": "name1",
       "error1": 2,
       "error2": 1,
       "error3": 1 }
  }

,
{ stream : {"name": "name2",
       "error1": 1,
       "error2": 1,
       "error3": 1 }
  }

I would like to group it by name and sum every time some different combination of errors.

this is what I did in mongo, I need to create the following query dynamically in java

 db.collection.aggregate([{$group: {_id: "$stream.name",error1: {$sum:"$stream.error1"   },error2: {$sum: "$stream.error2" }}  ])

the thing is that every time I need different combinations of the errors:error1 with error2, only error 1 etc..

this is what I did: (the arguments in the "if" are some boolean values that I am getting)

  List<String>  totalError = new ArrayList<String>();   
  BasicDBObject group = new BasicDBObject( "$group", new BasicDBObject("_id","$stream.name" ));


    if (error1)
    {

        group.append("error1",new BasicDBObject ("$sum", "$stream.error1"  ));

    }

    if (error2)
    {
        group.append("error2",new BasicDBObject ("$sum", "$stream.error2"  ));

    }

    if (error3)
    {
        group.append("error3",new BasicDBObject ("$sum", "$stream.error3"  ));

    }

the problem is that I am getting:

    { "$group" : { "_id" : "$stream.name"} , "error1" : { "$sum: "$stream.error1"} , "error2" : { "$sum" : "$stream.error2"}

},

instead of:

      { "$group" : { "_id" : "$stream.name", "error1" : { "$sum: "$stream.error1"} , "error2" : { "$sum" : "$stream.error2"}}

if I knew what error combination I need I could use append in the constructor of group dbobject.. but I don't know the combination and I need to use the "ifs"

please look at it now.. I checked my query in mongo

Ohad
– Ohad

2018-01-31 12:44:24 +00:00
Commented Jan 31, 2018 at 12:44 — Ohad
– Ohad, Commented Jan 31, 2018 at 12:44

s7vr · Accepted Answer · 2018-01-31 13:15:09Z

1

Try

BasicDBObject fields = new BasicDBObject("_id","$stream.name" );
 if (error1)
    fields.append("error1",new BasicDBObject ("$sum","$stream.error1"));
 if (error2)
    fields.append("error2",new BasicDBObject ("$sum","$stream.error2"));
 if (error3)
    fields.append("error3",new BasicDBObject ("$sum","$stream.error3"));
BasicDBObject group = new BasicDBObject( "$group", fields);

You should use helper functions when possible.

List<BsonField> fieldAccumulators = new ArrayList<>();
if (error1)
    fieldAccumulators.add(Accumulators.sum("error1","$stream.error1"));
if (error2)
    fieldAccumulators.add(Accumulators.sum("error2","$stream.error2"));
if (error3)
   fieldAccumulators.add(Accumulators.sum("error3","$stream.error3"));
collection.aggregate(Arrays.asList(Aggregates.group("$stream.name", fieldAccumulators)));

edited Jan 31, 2018 at 13:15

answered Jan 31, 2018 at 13:00

s7vr

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1 Comment

s7vr Over a year ago

you are welcome. I've added alternative too to use helper functions to create group stage.

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