In sumprain/dbMapR: Functions and classes to access Database

library(dbMapR)

Requirement

Time stamping the time of row insertion is required to look for any merge conflict, when that row is to be updated at a later time. It becomes more relevant in a web based, multiple access and asynchronous database, where multiple users are accessing and changing a particular row in the database. R does not have any robust timestamp mechanism. Below, I give the details of using the time stamping mechanism built for this package.

Structure of the timestamp

Timestamps are basically a character with following specific format, to which a class attribute has been added to t_stamp.

yyyymmddhhmmss{may be a decimal mark followed by upto 6 digits}@@Olson_compatible_timezone

Example: 20151030123634.998@@UTC

cur_timestamp

We can make current timestamp using cur_timestamp function. It is the only way to create a timestamp (of t_stamp class). This makes sure that we cannot make timestamps corresponding to any other time point other than current time point. cur_timestamp function uses Sys.time function to get the current time point. We will have to add a time zone (through tz parameter), which should be one of the names mantioned in OlsonNames() function. Do check OlsonNames() to see for the valid tz names.

Coercion to other classes

as.character coerces the t_stamp object to character. The timestamp is stored in database as character.

as.POSIXct coerces the t_stamp object to POSIXct class.

t_stamp.character function coerces a character object into a t_stamp object given the format is conforming with t_stamp class as checked by the utility function check_format_tstamp.

Comparision between two timestamps

%earlier%, %later% and %same_time% are the function which compares two t_stamp objects for their chronological order. They return boolean value.

Examples

Making new timestamp

ts1 <- cur_timestamp(digits = 3L, tz = "Asia/Kolkata")

Converting timestamp into POSIXct

as.POSIXct(ts1)   # keep default tz
as.POSIXct(ts1, tz = "UTC")   # changing tz to UTC

Checking for chronological order of two timestamp objects

ts2 <- cur_timestamp(tz = "UTC")
ts3 <- cur_timestamp()

ts2 %later% ts3         # TRUE

ts2 is occuring before ts3, but it is occuring at UTC, whereas ts3 is occuring at Asia/Kolkata time zone (UTC - 5.5 hours). So, ts2 is occuring later than ts3.

sumprain/dbMapR documentation built on May 30, 2019, 8:37 p.m.