MongoDB: How to count a field if it's value matches a condition? - mongodb

Question

I have a document that includes a field like this:
{
...
log: [
{
utc_timestamp: ISODate("2014-11-15T10:26:47.337Z"),
type: "clicked"
},
{
utc_timestamp: ISODate("2014-10-15T16:12:51.959Z"),
type: "emailed"
},
{
utc_timestamp: ISODate("2014-10-15T16:10:51.959Z"),
type: "clicked"
},
{
utc_timestamp: ISODate("2014-09-15T04:59:19.431Z"),
type: "emailed"
},
{
utc_timestamp: ISODate("2014-09-15T04:58:19.431Z"),
type: "clicked"
},
],
...
}
How do I get the count of log entries of type "clicked" from this month, only if there is not a log entry of type "emailed" this month?
In other words, I want to find out which clicks have not been sent a related email.
So, in this example, the count would be 1 since the most recent "clicked" entry doesn't have an "emailed" entry.
Note: For this use case, clicks don't have unique IDs - this is all the data that is logged.

Answer 1

Use the following aggregation pipeline:
db.click_log.aggregate([
{ "$match" : { "log.type" : { "$ne" : "emailed" } } }, // get rid of docs with an "emailed" value in log.type and docs not from this month
{ "$unwind" : "$log" }, // unwind to get log elements as separate docs
{ "$project" : { "_id" : 1, "log" : 1, "month" : { "$month" : "$log.utc_timestamp" } } },
{ "$match" : { "log" : "clicked", "month" : <# of month> } }, // get rid of log elements not from this month and that aren't type clicked
{ "$group" : { "_id" : "$_id", "count" : { "$sum" : 1 } } } // collect clicked elements from same original doc and count number
])
This will return, for each document not having "emailed" as a value of log.type, the count of elements of the array log that have log.type value clicked and with timestamp from the current month. If you want a sliding 30-day period for month, change the $match to be a range query with $gt and $lt covering the desired time period.

Answer 2

You can use query something similar to below.
db.dbversitydotcom_col.aggregate([ { $unwind: “$log” },
{ $match: { “log.type” : “clicked”, "log.utc_timestamp" : "your required date" } },
{ $sort: { “Files.Size” : -1.0 } }, { $limit: 5.0 } ]).count()
Please refer to http://dbversity.com/mongodb-importance-of-aggregation-framework/ for more detailed explanation,