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Function: Keep the Last N User Items

      +

      Goal: Keep the last N user notifications seen related to a user ID (these could be any documents).

      • This function keepLastN demonstrates how to keep a user record with the last N activities.

      • Requires Eventing Storage (or metadata collection) and a "source" collection.

      • Needs a Binding of type "bucket alias" (as documented in the Scriptlet).

      • Will operate on any mutation with a key starting with "nu:" of the form "nu:#:#".

      • The key "nu:#:#" contains two numbers. The first # is an increasing notification number, the second # is the user ID.

      • 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.

      • For our test we will keep just the three (3) most recent notifications per user ID.

      • keepLastN

      • Input Data/Mutation

      • 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
      }