Truncated updated string with R DBI package - r

Question

I need to update a wide table on an SQL SERVER from R. So the package DBI seems to be very useful for that.
The problem is that the R data.frame contains strings of more than 3000 characters and when I use the DBI dbSendQuery function, all strings are truncated to 256 characters.
Here could be a code example :
con <- odbc::dbConnect(drv = odbc::odbc(),
dsn = '***',
UID = '***',
PWD = '***')
df = data.frame(TEST = paste(rep("A", 300), collapse=""),
TEST_ID = 1068858)
df$TEST = df$TEST %>% as.character
query = paste0('UPDATE MY_TABLE SET "TEST"=? WHERE TEST_ID=?')
update <- DBI::dbSendQuery(con, query)
DBI::dbBind(update, df)
DBI::dbClearResult(update)
odbc::dbDisconnect(con)
Then the following request return 256 instead of 300 :
SELECT LEN(TEST) FROM MY_TABLE WHERE TEST_ID = 1068858
NB : TEST is of type (varchar(max), NULL) and already contains strings of more than 256 chars.
Thanks in advance for any advice

Answer 1

In the end, I choose to get rid of sophisticated functions. A solution was to write the table in .csv file and bulk insert it into the database. Here is an example using RODBC package :
write.table(x = df,
file = "/path/DBI_error_test.csv",
sep = ";",
row.names = FALSE, col.names = FALSE,
na = "NULL",
quote = FALSE)
Query = paste("CREATE TABLE #MY_TABLE_TMP (
TEST varchar(max),
TEST_ID int
);
BULK INSERT #MY_TABLE_TMP
FROM 'C:\\DBI_error_test.csv'
WITH
(
FIELDTERMINATOR = ';',
ROWTERMINATOR = '\n',
BATCHSIZE = 500000,
CHECK_CONSTRAINTS
)
UPDATE R
SET R.TEST = #MY_TABLE_TMP.TEST
FROM MY_TABLE AS R
INNER JOIN #MY_TABLE_TMP ON #MY_TABLE_TMP.TEST_ID = R.TEST_ID;
DROP TABLE #MY_TABLE_TMP;
")
channel <- RODBC::odbcConnect(dsn = .DB_DSN_NAME,
uid = .DB_UID,
pwd = .DB_PWD)
RODBC::sqlQuery(channel = channel, query = query, believeNRows = FALSE)
RODBC::odbcClose(channel = channel)