This is the structure of BSON document I have in mongodb.
{
"tournament_id": "P1oi12mwj10b1b",
"matches": [
{
"date_order": 1,
"matches": [
{
"match_id": "1A4i0sp34"
"time_order": 1,
"win": "team1",
"team1": "bar",
"team2": "psg"
},
{
"match_id": "3A4j0sp26"
"time_order": 2,
"win": "",
"team1": "rma",
"team2": "sev"
}
]
},
{
"date_order": 2,
"matches": [
{
"match_id": "2B4k0sp29"
"time_order": 1,
"win": "",
"team1": "manU",
"team2": "manC"
},
{
"match_id": "4A4i0sp31"
"time_order": 2,
"win": "",
"team1": "chelsea",
"team2": "arsenal"
}
]
}
]
}
I want to make a notification system which sends notification whenever a match completes. In other words, whenever the value of win field changes, I want to catch which match was updated. I'm using mongodb change streams.
For example, if match with match_id 3A4j0sp26 just completed, I want to print that object.
{
"match_id": "3A4j0sp26"
"time_order": 2,
"win": "team2",
"team1": "rma",
"team2": "sev"
# If possible I also want to find these fields,
"tournament_id": "P1oi12mwj10b1b",
"date_order": 1
}
I tried doing this.
import pymongo
from bson.json_util import dumps
MONGO_URI = 'mongodb://localhost/mydb'
client = pymongo.MongoClient(MONGO_URI)
filters = [] # How to correctly set this filter ???
'''
What I already tried but failed
filters = [{
'$match': {
'$and': [
{'updateDescription.updatedFields.matches': {'$exists': 'true'}}, # This line needs fixing.
{'operationType': {'$in': ['replace', 'update']}}
]
}
}]
'''
change_stream = client.mydb.match.watch(filters)
for change in change_streams:
print(dumps(change))
I tried to debug without applying filters. I updated win field of match_id 3A4j0sp26 to team2.
I get this as result.
{
"_id": {
"_data": "8261252C2F000000012B022C0100296E5A1004D4D1F2A9AF33491089DE8C2A51537EBB46645F6964006461228AE88CF6743D054B8CEF0004"
},
"operationType": "replace",
"clusterTime": {
"$timestamp": {
"t": 1629826095,
"i": 1
}
},
"fullDocument": {
"_id": {
"$oid": "61228ae88cf6743d054b8cef"
},
"tournament_id": "P1oi12mwj10b1b",
"matches": [
{
"date_order": 1,
"matches": [
{
"match_id": "1A4i0sp34"
"time_order": 1,
"win": "team1", # This was updated earlier. I don't want this.
"team1": "bar",
"team2": "psg"
},
{
"match_id": "3A4j0sp26"
"time_order": 2,
"win": "team1", # This is the most recently updated.
"team1": "rma",
"team2": "sev"
}
]
}]
}
}
It shows all elements from the array and not the one which was just updated.
Edited
Result I got after updating "score" field only.
{
"_id": {
"_data": "8261254598000000022B022C0100296E5A1004D4D1F2A9AF33491089DE8C2A51537EBB46645F6964006461228AE88CF6743D054B8CEF0004"
},
"operationType": "update",
"clusterTime": {
"$timestamp": {
"t": 1629832600,
"i": 2
}
},
"ns": {
"db": "mydb",
"coll": "match"
},
"documentKey": {
"_id": {
"$oid": "61228ae88cf6743d054b8cef"
}
},
"updateDescription": {
"updatedFields": {
"matches": [
{
"date_order": 1,
"matches": [
{
"match_id": "1A4i0sp34"
"time_order": 1,
"win": "team1",
"team1": "bar",
"team2": "psg"
},
{
"match_id": "3A4j0sp26"
"time_order": 2,
"win": "team1",
"team1": "rma",
"team2": "sev"
}
]
}]
},
"removedFields": []
}
}
}
It depends on how you do the update.
A short test to demonstrate:
Insert a document and start a change stream
PRIMARY> db.updtest.insert({list:[
{item:"1",state:"running"},
{item:"2",state:"done"},
{item:"3",state:"unknown"}
]});
WriteResult({ "nInserted" : 1 })
PRIMARY> let stream = db.updtest.watch()
Updating by setting the list field results in a change event that returns the entire array:
PRIMARY> db.updtest.updateOne({},{$set:{list:[
{item:"1",state:"running"},
{item:"2",state:"done"},
{item:"3",state:"running"}
]}});
{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }
PRIMARY> stream.next();
{
"_id" : {
"_data" : "82612577BE000000012B022C0100296E5A100436BFE3F91AF84C7CB04826F361BCE50346645F696400646125779D98787C286C5443050004"
},
"operationType" : "update",
"clusterTime" : Timestamp(1629845438, 1),
"ns" : {
"db" : "test",
"coll" : "updtest"
},
"documentKey" : {
"_id" : ObjectId("6125779d98787c286c544305")
},
"updateDescription" : {
"updatedFields" : {
"list" : [
{
"item" : "1",
"state" : "running"
},
{
"item" : "2",
"state" : "done"
},
{
"item" : "3",
"state" : "running"
}
]
},
"removedFields" : [ ]
}
}
Updating just one field in one subdocument results in a change event that include only the modified field:
PRIMARY> db.updtest.update({"list.item":"3"},{$set:{"list.$.state":"done"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
PRIMARY> stream.next();
{
"_id" : {
"_data" : "8261257879000000012B022C0100296E5A100436BFE3F91AF84C7CB04826F361BCE50346645F696400646125779D98787C286C5443050004"
},
"operationType" : "update",
"clusterTime" : Timestamp(1629845625, 1),
"ns" : {
"db" : "test",
"coll" : "updtest"
},
"documentKey" : {
"_id" : ObjectId("6125779d98787c286c544305")
},
"updateDescription" : {
"updatedFields" : {
"list.2.state" : "done"
},
"removedFields" : [ ]
}
}
If you also use the change stream option to return the full documents, you will have the context around the field that was changed.