R/db_connections.R

In ashoksiri/twitteR: R Based Twitter Client

require_package = function(package_name) {
  if (!require(package_name, character.only=TRUE, quietly=TRUE)) {
    stop(package_name, " is required to be installed for this activity")
  }
}

supported_db_handle_classes = c("SQLiteConnection", "MySQLConnection")

# Based on the class of db_handle, make sure the appropriate dbi backend
# package exists
require_dbi_package = function(db_handle) {
  if (!inherits(db_handle, supported_db_handle_classes)) {
    stop("db_handle must be one of the following classes: ", 
         paste(supported_db_handle_classes, collapse=", "))
  }
  
  switch(class(db_handle),
         SQLiteConnection = require_package("RSQLite"),
         MySQLConnection = require_package("RMySQL")
         )
  
  TRUE
}

# Convenience function which will wrap some of the DBI commands to get a SQLiteConnection
register_sqlite_backend = function(sqlite_file, ...) {
  if (!requireNamespace("RSQLite")) {
    stop("RSQLite package must be installed to generate an SQLite handle")
  }
  
  register_db_backend(dbConnect(RSQLite::SQLite(), sqlite_file, ...))
}

# Convenience function which will wrap the DBI command for a MySQL connection
register_mysql_backend = function(db_name, host, user, password, ...) {
  if (!requireNamespace("RMySQL")) {
    stop("RMySQL package must be installed to generate a MySQL handle")
  }
  
  db_handle = register_db_backend(dbConnect(RMySQL::MySQL(), user=user, password=password, 
                                  dbname=db_name, host=host, ...))
  dbGetQuery(db_handle, "SET NAMES 'utf8'")
  
  invisible(db_handle)
}


register_db_backend = function(db_handle) {
  require_dbi_package(db_handle)
  assign("db_handle", db_handle, envir=db_backend_cache)  
}

has_db_backend = function() {
  exists("db_handle", envir=db_backend_cache)
}

get_db_backend = function() {
  if (!has_db_backend()) {
    stop("No DB backend has been registered, see ?register_db_backend")
  }
  
  get("db_handle", envir=db_backend_cache)
}