UpdateListener-class: Class '"UpdateListener"'

In ralmond/Proc4: Four Process Assessment Database and Dispatcher

Class "UpdateListener"

Description

This Listener updates an existing record (in a Mongo collection) for the student (uid), with the contents of the data (details) field of the message.

Details

The database is a mongo collection identified by dburi, dbname and colname (collection within the database). The mess field of the P4Message is checked against the applicable messages in messSet. If it is there, then the record in the database corresponding to the qfields (by default app(mess) and uid(mess)) is updated. Specifically, the field targetField is set to details(mess). The function jsonEncoder is called to encode the target field as a JSON object for injection into the database.

If targetField="", then the behavior is slightly different. Instead the fields in details(mess) (labeled by their names) are updated.

Extends

This class implements the Listener interface.

All reference classes extend and inherit methods from "envRefClass".

Methods

isListener

signature(x = "UpdateListener"): TRUE

receiveMessage

signature(x = "UpdateListener", message): If the message is in the messSet, it updates the record corresponding to app(mess) and uid(mess) in the database with the contents of details(mess). (See details.)

listenerName

signature(x = "UpdateListener"): Returns the name assigned to the listener.

listenerDataTable

signature(listener = "UpdateListener", appid ): Builds a data datable from the messages.

Data Table

When the listenerDataTable method is called, the table is made by applying mdbFind to the target column. The behavior is different depending on whether or not a targetField is specified. If there is no target field, then all fields of the column are returned.

If there is a targetField, then the jsonDecoder function is applied to its value, and it is joined with the app, uid, context, timestamp fields from the header to make the data table.

Fields

dbname:

Object of class character giving the name of the Mongo database

dburi:

Object of class character giving the url of the Mongo database.

colname:

Object of class character giving the column of the Mongo database.

messSet:

A vector of class character giving the name of messages which are sent to the database. Only messages for which mess(mess) is an element of messSet will be inserted.

db:

Object of class MongoDB giving the database. Use messdb() to access this field to makes sure it has been set up.

qfields:

Object of class character giving the names of the fields which should be considered a key for the messages.

targetField:

Object of class character naming the field which is to be set.

jsonEncoder:

A function or a non-empty character scalar naming a function which will be used to encode details(mess) as a JSON object. The default is unparseData.

decoderEncoder:

A function or character scalar naming a function which will be used to decode the target field when building a data table. The default is parseData.

Class-Based Methods

messdb():

Accessor for the database collection. Initializes the connection if it has not been set up.

receiveMessage(mess):

Does the work of updating the database. See Details.

reset(app):

Empties the database collection of messages with this app id.

initialize(sender, dbname, dburi, colname, messSet, ...):

Sets default values for fields.

Author(s)

Russell Almond

References

This is an example of the observer design pattern. https://en.wikipedia.org/wiki/Observer_pattern.

See Also

Listener, P4Message, UpdateListener, InjectionListener, CaptureListener, UpsertListener, TableListener, mongo

The function unparseData is the default encoder.

Examples

## Updating the data field.
fm <- mongo::fake_mongo(count=list(0L,1L))
ul <- UpdateListener("tester", db=fm,messSet=c("Scored Response"))

## New message, insert
  mess1 <- P4Message("Fred","Task 1","Evidence ID","Scored Response",
                     as.POSIXct("2018-11-04 21:15:25 EST"),
                     list(correct=TRUE,selection="D"))
receiveMessage(ul,mess1)

## Message is update, update.
mess1a <- P4Message("Fred","Task 1","Evidence ID","Scored Response",
                     as.POSIXct("2018-11-04 21:15:40 EST"),
                     list(correct=TRUE,selection="D",key="D"))
receiveMessage(ul,mess1a)

### No target field, details are added to record.

data2json <- function(dat) {
  jsonlite::toJSON(mongo::unboxer(dat))
}

upwind <- UpdateListener(messSet=c("Money Earned","Money Spent"),
                         db=mongo::MongoDB("Players",noMongo=TRUE),
                         targetField="",
                         jsonEncoder="data2json")

mess2 <- P4Message(app="default",uid="Phred",context="Down Hill",
                   sender="EIEvent",mess="Money Earned",
                   details=list(trophyHall=list(list("Down Hill"="gold"),
                                                list("Stairs"="silver")),
                                bankBalance=10))

receiveMessage(upwind,mess2)

ralmond/Proc4 documentation built on June 13, 2025, 7:13 a.m.