Goal: Keep the last N user notifications seen related to a user ID (these could be any documents).
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This function keepLastN demonstrates how to keep a user record with the last N activities.
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Requires Eventing Storage (or metadata collection) and a "source" collection.
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Needs a Binding of type "bucket alias" (as documented in the Scriptlet).
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Will operate on any mutation with a key starting with "nu:" of the form "nu:#:#".
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The key "nu:#:#" contains two numbers. The first # is an increasing notification number, the second # is the user ID.
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Anytime we insert a new record we want to remove the earliest notification record for the user so we only have at most N records for each user. We assume that nid always increases across time as such we ignore duplicates.
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For our test we will keep just the three (3) most recent notifications per user ID.
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keepLastN
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Input Data/Mutation
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Output Data/Mutation
Two variants of this function are available a 6.6 version (this Function) that implements userspace CAS and a 6.6.1+/7.0.0+ version which uses true CAS
keepLastN (userspace CAS)
// To run configure the settings for this Function, keepLastN, as follows:
//
// Version 7.0+
// "Listen to Location"
// bulk.data.source
// "Eventing Storage"
// rr100.eventing.metadata
// Binding(s)
// 1. "binding type", "alias name...", "bucket.scope.collection", "Access"
// "bucket alias", "src_col", "bulk.data.source", "read and write"
//
// Version 6.X
// "Source Bucket"
// source
// "MetaData Bucket"
// metadata
// Binding(s)
// 1. "binding type", "alias name...", "bucket", "Access"
// "bucket alias", "src_col", "source", "read and write"
/*
* Process all mutations, however updateNotifyArrayInKV(...) will only
* data with KEYS like nu:#:#
*/
function OnUpdate(doc, meta) {
const MAX_RETRY = 16;
const MAX_ARRAY = 3;
const DEBUG = false;
updateNotifyArrayInKV(doc, meta, MAX_RETRY, MAX_ARRAY, DEBUG);
}
/*
* reads form KV and manipulates the result to only keep 'MAX_ARRAY' items
*/
function addToNtfyArray(src_col, user_id, insert_json, MAX_ARRAY, DEBUG) {
var ntfy_id = insert_json.nid;
var random_csum;
var user_doc = src_col["user_plus_ntfys:" + user_id];
if (!user_doc) {
// generate unique random #
random_csum = Math.random();
user_doc = { "type": "user_plus_ntfys", "id": user_id, "notifications" : [], "random": random_csum };
user_doc.notifications.push(insert_json);
} else {
if (user_doc.notifications[0].nid >= ntfy_id && user_doc.notifications.length === MAX_ARRAY) {
// do nothing this is older data, we assume that nid always increases
return null;
} else {
// find insert position
for(var i=0; i<=user_doc.notifications.length + 1 ; i++) {
if (i < user_doc.notifications.length && user_doc.notifications[i].nid === ntfy_id) {
// do nothing this is duplicate data we already have it, assume no updates to notifys
return null;
}
if (i == user_doc.notifications.length || user_doc.notifications[i].nid > ntfy_id) {
// add to array middle or end
user_doc.notifications.splice(i, 0, insert_json);
random_csum = Math.random();
// update unique random #
user_doc.random = random_csum;
break;
}
}
}
while (user_doc.notifications.length > MAX_ARRAY) {
// ensure proper size
user_doc.notifications.shift();
}
}
if (DEBUG) log("user_plus_ntfys:" + user_id,user_doc);
return user_doc;
}
/*
* creates, gets, and updates (via replace) the KV tracking array document
*/
function updateNotifyArrayInKV(doc, meta, MAX_RETRY, MAX_ARRAY, DEBUG) {
// will process ALL data like nu:#:#
var parts = meta.id.split(':');
if (!parts || parts.length != 3 || parts[0] != "nu") return;
var ntfy_id = parseInt(parts[1]);
var user_id = parseInt(parts[2]);
//log("Doc created/updated " + meta.id + " ntfy_id " + ntfy_id + " user_id " + user_id);
var insert_json = {"nid": ntfy_id, doc};
// this is a can be improved in version 6.6.1 as CAS operations are supported.
// we utilize a 'random' tag in the document itself to emulate a CAS operation.
for (var tries=0; tries < 16; tries++) {
var user_doc = addToNtfyArray(src_col, user_id, insert_json, MAX_ARRAY, DEBUG);
if (user_doc == null) {
// do nothing
return;
}
var random_csum = user_doc.random;
// this is a read write alias to the functions source bucket, write then reread
src_col["user_plus_ntfys:" + user_id] = user_doc;
user_doc = src_col["user_plus_ntfys:" + user_id];
// we use the random values to perform a CAS, we give up after 16 attempts
if (random_csum !== user_doc.random) {
// failure need to retry
tries++;
if (DEBUG) log("CAS like operation failed: tries "+tries+
" random_csum:",random_csum,"!==", "user_doc.random",user_doc.random);
} else {
// success could even delete the input notification doc here
if (DEBUG) log("CAS like operation success: tries "+tries+
" random_csum:",random_csum,"!==", "user_doc.random",user_doc.random);
return;
}
}
log ("FAILED to insert id: " + meta.id, doc)
}We want to create a test doc set
| key | data |
|---|---|
nu:1:1 |
{"somekey":"someValue"} |
nu:2:2 |
{"somekey":"someValue"} |
nu:3:1 |
{"somekey":"someValue"} |
nu:4:1 |
{"somekey":"someValue"} |
nu:5:1 |
{"somekey":"someValue"} |
nu:6:2 |
{"somekey":"someValue"} |
nu:7:2 |
{"somekey":"someValue"} |
nu:8:1 |
{"somekey":"someValue"} |
nu:9:2 |
{"somekey":"someValue"} |
nu:10:2 |
{"somekey":"someValue"} |
Use the Query Editor to insert the above data items (you do not need an Index)
UPSERT INTO `bulk`.`data`.`source` (KEY,VALUE)
VALUES ( "nu:1:1", {"somekey":"someValue"} ),
VALUES ( "nu:2:2", {"somekey":"someValue"} ),
VALUES ( "nu:3:1", {"somekey":"someValue"} ),
VALUES ( "nu:4:1", {"somekey":"someValue"} ),
VALUES ( "nu:5:1", {"somekey":"someValue"} ),
VALUES ( "nu:6:2", {"somekey":"someValue"} ),
VALUES ( "nu:7:2", {"somekey":"someValue"} ),
VALUES ( "nu:8:1", {"somekey":"someValue"} ),
VALUES ( "nu:9:2", {"somekey":"someValue"} ),
VALUES ( "nu:10:2", {"somekey":"someValue"} );NEW/OUTPUT: KEY user_plus_ntfys:1
Note, we add/create the property _random_ in the tracking doc as we use _random_ is used to emulate CAS.
{
"type": "user_plus_ntfys",
"id": 1,
"notifications": [{
"nid": 4,
"doc": {
"somekey": "someValue"
}
}, {
"nid": 5,
"doc": {
"somekey": "someValue"
}
}, {
"nid": 8,
"doc": {
"somekey": "someValue"
}
}],
"random": 0.9071605464143964
}
NEW/OUTPUT: KEY user_plus_ntfys:2
{
"type": "user_plus_ntfys",
"id": 2,
"notifications": [{
"nid": 7,
"doc": {
"somekey": "someValue"
}
}, {
"nid": 9,
"doc": {
"somekey": "someValue"
}
}, {
"nid": 10,
"doc": {
"somekey": "someValue"
}
}],
"random": 0.5637501636850883
}