How to properly handle timezone when passing POSIXct objects between R and Postgres DBMS? -


i struggling understand happens behind scenes when passing posixct objects between r , postgres using rpostgresql. in following example, define 2 timestamp fields: 1 with timezone other 1 without. however, appears treated same when passing posixct objects via dbwritetable , dbreadtable.

library(rpostgresql)  drv <- dbdriver("postgresql") con <- dbconnect(drv, host = "127.0.0.1", port = "5432", user= "postgres",                  dbname = "test_db")  q <- " create table test_table (   dttm timestamp without time zone,   dttmtz timestamp time zone )" dbsendquery(con, q)  # using timezone cet dttm <- as.posixct("2016-01-01 10:20:10", tz="cet") df <- data.frame(dttm = dttm, dttmtz = dttm) dbwritetable(con, "test_table", df, overwrite=false, append=t, row.names=0)  # using timezone utc     dttm <- as.posixct("2016-01-01 14:20:10", tz="utc") df <- data.frame(dttm = dttm, dttmtz = dttm) dbwritetable(con, "test_table", df, overwrite=false, append=t, row.names=0)  df2 <- dbreadtable(con, "test_table")

both fields come out same. appears if timezones discarded.

df2$dttm [1] "2016-01-01 10:20:10 cet" "2016-01-01 14:20:10 cet"  df2$dttmtz "2016-01-01 10:20:10 cet" "2016-01-01 14:20:10 cet"

questions:

  1. what goes on behind scenes?
  2. how can pass posixct's timezone , forth?

i think you've pointed out bug in rpostgresql: not seem getting time zone r posixct objects.

modifying code:

library(rpostgresql)  drv <- dbdriver("postgresql") con <- dbconnect(drv,  port = "5432", user= "postgres",                  dbname = "test")  # timestamps in 3 different time zones dt1 <- as.posixct("2016-01-01 10:20:10", tz="us/eastern") dt2 <- as.posixct("2016-01-01 10:20:10", tz="utc") dt3 <- as.posixct("2016-01-01 10:20:10", tz="asia/tokyo") df <- data.frame(dt1=dt1, dt2=dt2, dt3=dt3)  q <- " create table test_table (   dt1 timestamp time zone,   dt2 timestamp time zone,   dt3 timestamp time zone,   primary key (dt1) )" dbsendquery(con, q)  dbwritetable(con, "test_table", df, overwrite=false, append=t, row.names=0)  df2 <- dbreadtable(con, "test_table")

note 3 timestamps equal timezones not handled correctly

df2$dt1

"2016-01-01 10:20:10 est" 

df2$dt2

"2016-01-01 10:20:10 est" 

df2$dt3

"2016-01-01 10:20:10 est"

and same true in postgres - seen in pgadmin here enter image description here

this suggests postgres not getting timezone r

note if manually change 1 time zone in test_table (e.g., first record in pgadmin)

eg, enter image description here

and fetch 

df2 <- dbreadtable(con, "test_table")

then timezone correctly handled

df2$dt1

"2016-01-01 05:20:10 est"

df2$dt2

"2016-01-01 10:20:10 est"

df2$dt3

"2016-01-01 10:20:10 est"

so suggets rpostgresql not correctly passing time zone information postgres rpostgresql correctly getting time zone information postgres.


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