filehashSQLite-class {filehashSQLite}

Class "filehashSQLite"

Description

Create a 'filehash' database using SQLite as the backend

Details

The “filehashSQLite” class represents a “filehash” key-value database using the SQLite DBM as the backend. Objects are stored in a single SQLite database table along with their keys.

Objects from the Class

Objects can be created by calls of the form new("filehashSQLite", ...). More likely, one will use the functions dbCreate and dbInit from the filehash package.

Slots

datafile

character, full path to the file in which the database should be stored

dbcon

Object of class “SQLiteConnection”, a SQLite connection

drv

‘SQLite’ driver

name

character, the name of the database

Extends

Class "filehash", directly.

Methods

dbDelete

signature(db = "filehashSQLite", key = "character"): delete a key-value pair from the database

dbExists

signature(db = "filehashSQLite", key = "character"): check the existence of a specific key or vector of keys

dbFetch

signature(db = "filehashSQLite", key = "character"): retrieve the value associated with a specific key

dbInsert

signature(db = "filehashSQLite", key = "character"): insert a key-value pair

dbList

signature(db = "filehashSQLite"): return character vector of keys currently stored in the database

dbUnlink

signature(db = "filehashSQLite"): delete the entire database

dbMultiFetch

signature(db = "filehashSQLite", key = "character"): return (as a named list) the values associated with a vector of keys

Note

“filehashSQLite” databases have a "[" method that can be used to extract multiple elements in an efficient manner. The return value is a list with names equal to the keys passed to "[". If there are keys passed to "[" that do not exist in the database, a warning is given.

The “SQLite” format for filehash uses an ASCII serialization of the data which could result in some rounding error for floating point numbers.

Note that if you use keys that are numbers coerced to character vectors, then you may have trouble with them being coerced to numeric. The SQLite database will see these key values and automatically convert them to numbers.

Author(s)

Roger D. Peng

Examples

library(filehashSQLite)

dbCreate("myTestDB", type = "SQLite")
db <- dbInit("myTestDB", type = "SQLite")

set.seed(100)
db$a <- rnorm(100)
db$b <- "a character element"

with(db, mean(a))

cat(db$b, "\n")

dbUnlink(db)