CODEWITHSUNDEEP
mongodbaggregation-framework
Damo
Damo

Reputation: 11550

MongoDB Aggregation $group and categorise

I have a set of data like this:

> db.esbtrans.find().limit(2).pretty()
{
    "_id" : ObjectId("51fa56a509d013ddbd06f513"),
    "messageflow" : "TEST",
    "correlid" : "2b2bdc4f-24bc-412a-8438-9a7e0c256b38",
    "start" : ISODate("2013-08-01T12:37:57.452Z"),
    "finish" : ISODate("2013-08-01T12:38:17.452Z"),
    "response" : NumberLong(20000),
    "status" : "OK"
}
{
    "_id" : ObjectId("51fa56a509d013ddbd06f514"),
    "messageflow" : "TEST",
    "correlid" : "0565d123-3570-4ce9-83d7-86e50aad48c5",
    "start" : ISODate("2013-08-01T12:37:57.452Z"),
    "finish" : ISODate("2013-08-01T12:38:44.452Z"),
    "response" : NumberLong(47000),
    "status" : "ERR"
}
{
    "_id" : ObjectId("51fa56a509d013ddbd06f515"),
    "messageflow" : "TEST2",
    "correlid" : "d14c447a-eb4c-4a00-85fd-009955798386",
    "start" : ISODate("2013-08-01T12:37:57.452Z"),
    "finish" : ISODate("2013-08-01T12:38:57.452Z"),
    "response" : NumberLong(60000),
    "status" : "OK"
}
{
    "_id" : ObjectId("51fa56a509d013ddbd06f516"),
    "messageflow" : "TEST2",
    "correlid" : "3b7902ce-a8bb-496a-a67f-23b562554c16",
    "start" : ISODate("2013-08-01T12:37:57.452Z"),
    "finish" : ISODate("2013-08-01T12:38:50.452Z"),
    "response" : NumberLong(53000),
    "status" : "ERR"
}

Here are two elements of what would be tens of thousands of similar records, the key properties being "messageflow", "status" and a count of the combination. I want to get a result that looks like this:

[{
    "messageflow: "TEST",
    "errors": 1,
    "successes": 1
},{
    "messageflow: "TEST2",
    "errors": 1,
    "successes": 1
}]

I have got as far as an Aggregation like this:

> db.esbtrans.aggregate(
    {"$group": 
        {_id: {messageflow: "$messageflow", status: "$status"}, 
        resptot: {$sum: "$response"}, 
        count: {$sum: 1}}}, 
    {"$project": 
        {flow: "$_id.messageflow", 
        status: "$_id.status", 
        count: "$count", 
        _id: 0}})

Which produces a result like:

 {
    "result" : [
        {
            "count" : 240,
            "flow" : "TEST2",
            "status" : "ERR"
        },
        {
            "count" : 267,
            "flow" : "TEST",
            "status" : "ERR"
        },
        {
            "count" : 244,
            "flow" : "TEST",
            "status" : "OK"
        },
        {
            "count" : 249,
            "flow" : "TEST2",
            "status" : "OK"
        }
    ],
    "ok" : 1
}

However I can't see how I can $project each status ("OK" or "ERR") onto the correct output so that they are fields on a record identified by "messageflow". Any ideas?

Upvotes: 0

Views: 379

Answers (1)

Miguel Cartagena
Miguel Cartagena

Reputation: 2606

Damo, one thing that you must keep in mind is that when you want to group by a value, you probably have to use $cond operator.

db.esbtrans.aggregate({ 
    $group : { 
        _id : "$messageflow",
        errors : { $sum : {  $cond : [ { $eq : ["$status", "ERR"] } ,1,0] } },
        successes : { $sum : {  $cond : [ { $eq : ["$status", "OK"] } ,1,0] } },
    } 
})

Explaining: I group by messageflow because this field is your basic axis. Then to count the number of erros and successes, I use the $sum operator in combination with $cond and $eq. It just compares if status is ERR or OK and sum properly.

Upvotes: 3

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