RMySQL (version 0.4-6)

dbManager: Instantiate a database manager

Description

This function creates an object that allows you to connect to the Database Systems (DBMS) specified in its argument.

Usage

dbManager(obj, ...)

Arguments

obj

a character string specifying the DBMS, e.g., "MySQL", "Oracle", "SQLite".

...

additional parameters may be specified for the actual database engine. E.g., the Oracle implementation allows you to specify the maximum number of open connection and a default maximum number of records to be transferred from the database. See the indiv

Value

• An object that extends dbManager and dbObjectId in a database-specific manner. For instance dbManager("Oracle") produces an object of class OraManager and is equivalent to using Oracle. Similarly dbManager("Oracle") produces an OraManager object and its equivalent to invoking Oracle.

  This object is required to create connections to one or several database engines.

Side Effects

The R/S client part of the database communication is initialized, connecting to the database engine needs to be done through calls to dbConnect.

References

See the Omega Project for Statistical Computing at http://www.omegahat.org for more details on the R/S database interface.

Details

This object is a singleton, that is, if you invoke this function again, it will return the same initialized object.

See Also

On database managers:

dbManager MySQL load unload

On connections, SQL statements and resultSets:

dbExecStatement dbExec fetch quickSQL

On transaction management:

commit rollback

On meta-data:

describe getVersion getDatabases getTables getFields getCurrentDatabase getTableIndices getException getStatement hasCompleted getRowCount getAffectedRows getNullOk getInfo

Examples

# create a Oracle instance and create one connection.
> m <- dbManager("Oracle")
> m
OraManager id = (7269) 

# open the connection using user, passsword, etc., as
# specified in the file \file{\$HOME/.my.cnf}
> con <- dbConnect(m)    

# Let's look at the status of the manager
> describe(m, verbose = F)   
OraManager id = (7269) 
  Max  connections: 16 
  Conn. processed: 1 
  Default records per fetch: 500 
  Open connections: 1 

# Run an SQL statement by creating first a resultSet object
> rs <- dbExecStatement(con, 
         statement = "SELECT w.laser_id, w.wavelength, p.cut_off 
                      FROM WL w, PURGE P
                      WHERE w.laser_id = p.laser_id
                      SORT BY w.laser_id")
> rs
OraResultSet id = (12629,1,3)

# we now fetch records from the restulSet into a data.frame
> data <- fetch(rs, n = -1)   # extract all rows
> dim(data)
[1] 1779  18

# Extract meta-data information.  What Ora databases are there 
# available on host "wyner"
> getDatabases(m, host = "wyner")
   Database 
1     mysql
2      opto
3      test
4 iptraffic
5     fraud

> # What tables are there in the "opto" database? 
> dbTables(m, dbname = "opto", host = "wyner")
  Tables in opto 
1           PBCT
2          PURGE
3             WL
4          liv25
5          liv85