dbframe-class: Class '"dbframe"'

In grayclhn/dbframe-R-library: An R to SQL interface

Description

Each “dbframe” object references a particular table inside an sql database. The class and its methods are designed to query and manipulate the table easily inside R.

Objects from the Class

Objects can be created by calls of the form new("dbframe", ...), but I recommend that you use the constructor dbframe.

The dbframe{\char95}sqlite class creates a link to a table in an sqlite database, and dbframe acts as a superclass. dbframe{\char95}sqlite{\char95}temporary implements temporary sqlite databases. I'd like to add other classes that store links to other databases (i.e. Mysql and Postgresql) as well. Until then, dbframe also works as an experimental class that tries to guess how to open a connection to the right database—please let me know how well it works, or if it works at all.

Slots

dbframe

dbConnect.arguments:

Object of class "list", a list of arguments to pass to dbConnect when it's time to connect to the database.

readonly:

Object of class "logical" that indicates whether the user is allowed to write to the database. Be careful! This is implemented only as a safeguard against carelessness; it is still very easy to write to the table.

table:

Object of class "character", the name of the table associated with this dbframe object.

Additional slots for dbframe_sqlite

dbname:

Object of class "character", the filename of the associated SQLite database.

rowid:

Object of class "integer", the rowid of the last value inserted into the table.

Methods

dbframe

clear

signature(... = "dbframe"): Remove the table corresponding to the dbframe object from its database. Please see the clear documentation for details.

dbname

signature(x = "dbframe_sqlite"): Returns the filename of the sqlite database associated with the object.

<<Define "dbname" method>>=
    setMethod("dbname", signature = c("dbframe"), function(x) x@dbname)

dbConnect

signature(drv = "dbframe"): Establishes a connection with the database associated with the object.

<<Define "dbConnect" method for "dbframe">>=
    setMethod("dbConnect", signature = "dbframe", 
              definition = function(drv,...)
              do.call("dbConnect", [e-mail]))

insert<-

signature(x = "dbframe"): Insert records into the dbframe table. Please see individual documentation for details.

readonly

signature(x = "dbframe"): Determine whether the dbframe object is read-only.

<<Define "readonly" method>>=
    setMethod("readonly", signature = c("dbframe"), function(x) x@readonly)

select

Query the dbframe table. Please see individual documentation for details.

tablename

signature(x = "dbframe"): Returns the table name associated with the object.

<<Define "tablename" method>>=
    setMethod("tablename", signature = c("dbframe"), function(x) x@table)

is.linked

signature(x = "dbframe"): Check whether the table associated with the dbframe exists.

<<Define "is.linked" method>>=
    setMethod("is.linked", signature = c("dbframe"), function(x,...) {
      dbc <- dbConnect(x,...)
      answer <- tablename(x) %in% dbListTables(dbc)
      dbDisconnect(dbc)
      return(answer)
    })

For dbframe_sqlite

dbConnect

signature(drv = "dbframe_sqlite"): Establishes a connection with the database associated with the object.

<<Define "dbConnect" method for "dbframe_sqlite">>=
    setMethod("dbConnect", signature = "dbframe_sqlite", 
      definition = function(drv,...) return(do.call("dbConnect",
        c(drv = "SQLite", dbname = dbname(drv), list(...),
          dbConnect.arguments = [e-mail]))))

rowid

signature(x = "dbframe_sqlite"): Returns the rowid associated with the last insert.

<<Define "rowid" method>>=
    setMethod("rowid", signature = c("dbframe_sqlite"), 
              function(x,...) x@rowid)

rowid<-

signature(x = "dbframe_sqlite"): Assigns the rowid associated with the last insert.

<<Define "rowid<-" method>>=
    setMethod("rowid<-", signature = c("dbframe_sqlite"), function(x,...,value) {
      x@rowid <- as.integer(value)
      return(x)})

S3 Methods

as.data.frame

as.data.frame.dbframe: Coerce a dbframe object to a data frame.

<<Define "as.data.frame" method>>=
    as.data.frame.dbframe <- function(x,...) select(x,...)

dim

dim.dbframe: Determine the number of rows and columns in a dbframe.

<<Define "dim" method>>=
    dim.dbframe <- function(x) {
      nrows <- select(x, "count(*)")[[1]]
      ncols <- length(select(x, limit = 0))
      c(nrows, ncols)
    }

Implementation

The basic definition of these classes is straightforward. Individual methods are defined above; I'll define the generic functions here as necessary; note that the generic function for dbConnect is defined in the DBI package.

<<*>>=
    setClass("dbframe", representation(table = "character",
                                       readonly = "logical",
                                       dbConnect.arguments = "list"))

    setClass("dbframe_sqlite", contains = "dbframe",
             representation(rowid = "integer", dbname = "character"))

    <<Define "dbConnect" method for "dbframe">>
    <<Define "dbConnect" method for "dbframe_sqlite">>
 
    <<Define "as.data.frame" method>>
    <<Define "dim" method>>
  
    setGeneric("tablename", function(x) standardGeneric("tablename"))
    <<Define "tablename" method>>
    setGeneric("dbname", function(x) standardGeneric("dbname"))
    <<Define "dbname" method>>
    setGeneric("readonly", function(x) standardGeneric("readonly"))
    <<Define "readonly" method>>
    setGeneric("is.linked", function(x,...) standardGeneric("is.linked"))
    <<Define "is.linked" method>>
    setGeneric("rowid", function(x,...) standardGeneric("rowid"))
    <<Define "rowid" method>>
    setGeneric("rowid<-", function(x,...,value) standardGeneric("rowid<-"))
    <<Define "rowid<-" method>>

Author(s)

Gray Calhoun [e-mail]

See Also

dbframe, clear, insert<-, select

grayclhn/dbframe-R-library documentation built on May 17, 2019, 8:33 a.m.