module SQLite3
# The Database class encapsulates a single connection to a SQLite3 database.
# Its usage is very straightforward:
#
# require "sqlite3"
#
# db = SQLite3::Database.new("data.db")
#
# db.execute("select * from table") do |row|
# p row
# end
#
# db.close
#
# It wraps the lower-level methods provides by the selected driver, and
# includes the Pragmas module for access to various pragma convenience
# methods.
#
# The Database class provides type translation services as well, by which
# the SQLite3 data types (which are all represented as strings) may be
# converted into their corresponding types (as defined in the schemas
# for their tables). This translation only occurs when querying data from
# the database--insertions and updates are all still typeless.
#
# Furthermore, the Database class has been designed to work well with the
# ArrayFields module from Ara Howard. If you require the ArrayFields
# module before performing a query, and if you have not enabled results as
# hashes, then the results will all be indexible by field name.
class Database
include Pragmas
class << self
alias :open :new
# Quotes the given string, making it safe to use in an SQL statement.
# It replaces all instances of the single-quote character with two
# single-quote characters. The modified string is returned.
def quote(string)
string.gsub(/'/, "''")
end
end
# The low-level opaque database handle that this object wraps.
attr_reader :handle
# A reference to the underlying SQLite3 driver used by this database.
attr_reader :driver
# A boolean that indicates whether rows in result sets should be returned
# as hashes or not. By default, rows are returned as arrays.
attr_accessor :results_as_hash
# Encoding used to comunicate with database.
attr_reader :encoding
# Create a new Database object that opens the given file. If utf16
# is +true+, the filename is interpreted as a UTF-16 encoded string.
#
# By default, the new database will return result rows as arrays
# (#results_as_hash) and has type translation disabled (#type_translation=).
def initialize(file_name, options = {})
@encoding = Encoding.find(options.fetch(:encoding, "utf-8"))
load_driver(options[:driver])
@statement_factory = options[:statement_factory] || Statement
result, @handle = @driver.open(file_name, Encoding.utf_16?(@encoding))
Error.check(result, self, "could not open database")
@closed = false
@results_as_hash = options.fetch(:results_as_hash, false)
end
# Return +true+ if the string is a valid (ie, parsable) SQL statement, and
# +false+ otherwise
def complete?(string)
@driver.complete?(string)
end
# Return a string describing the last error to have occurred with this
# database.
def errmsg
@driver.errmsg(@handle)
end
# Return an integer representing the last error to have occurred with this
# database.
def errcode
@driver.errcode(@handle)
end
# Closes this database.
def close
unless @closed
result = @driver.close(@handle)
Error.check(result, self)
end
@closed = true
end
# Returns +true+ if this database instance has been closed (see #close).
def closed?
@closed
end
# Returns a Statement object representing the given SQL. This does not
# execute the statement; it merely prepares the statement for execution.
#
# The Statement can then be executed using Statement#execute.
#
def prepare(sql)
stmt = @statement_factory.new(self, sql, Encoding.utf_16?(@encoding))
if block_given?
begin
yield stmt
ensure
stmt.close
end
else
return stmt
end
end
# Executes the given SQL statement. If additional parameters are given,
# they are treated as bind variables, and are bound to the placeholders in
# the query.
#
# Note that if any of the values passed to this are hashes, then the
# key/value pairs are each bound separately, with the key being used as
# the name of the placeholder to bind the value to.
#
# The block is optional. If given, it will be invoked for each row returned
# by the query. Otherwise, any results are accumulated into an array and
# returned wholesale.
#
# See also #execute2, #query, and #execute_batch for additional ways of
# executing statements.
def execute(sql, *bind_vars)
prepare(sql) do |stmt|
result = stmt.execute(*bind_vars)
if block_given?
result.each { |row| yield row }
else
return result.inject([]) { |arr, row| arr << row; arr }
end
end
end
# Executes the given SQL statement, exactly as with #execute. However, the
# first row returned (either via the block, or in the returned array) is
# always the names of the columns. Subsequent rows correspond to the data
# from the result set.
#
# Thus, even if the query itself returns no rows, this method will always
# return at least one row--the names of the columns.
#
# See also #execute, #query, and #execute_batch for additional ways of
# executing statements.
def execute2(sql, *bind_vars)
prepare(sql) do |stmt|
result = stmt.execute(*bind_vars)
if block_given?
yield result.columns
result.each { |row| yield row }
else
return result.inject([result.columns]) { |arr,row| arr << row; arr }
end
end
end
# A convenience method for obtaining the first row of a result set, and
# discarding all others. It is otherwise identical to #execute.
#
# See also #get_first_value.
def get_first_row(sql, *bind_vars)
execute(sql, *bind_vars) { |row| return row }
nil
end
# A convenience method for obtaining the first value of the first row of a
# result set, and discarding all other values and rows. It is otherwise
# identical to #execute.
#
# See also #get_first_row.
def get_first_value(sql, *bind_vars)
execute(sql, *bind_vars) { |row| return row[0] }
nil
end
# Obtains the unique row ID of the last row to be inserted by this Database
# instance.
def last_insert_row_id
@driver.last_insert_rowid(@handle)
end
# Returns the number of changes made to this database instance by the last
# operation performed. Note that a "delete from table" without a where
# clause will not affect this value.
def changes
@driver.changes(@handle)
end
# Indicates that if a request for a resource terminates because that
# resource is busy, SQLite should sleep and retry for up to the indicated
# number of milliseconds. By default, SQLite does not retry
# busy resources. To restore the default behavior, send 0 as the
# +ms+ parameter.
#
# See also the mutually exclusive #busy_handler.
def busy_timeout(ms)
result = @driver.busy_timeout(@handle, ms)
Error.check(result, self)
end
# Begins a new transaction. Note that nested transactions are not allowed
# by SQLite, so attempting to nest a transaction will result in a runtime
# exception.
#
# The +mode+ parameter may be either <tt>:deferred</tt> (the default),
# <tt>:immediate</tt>, or <tt>:exclusive</tt>.
#
# If a block is given, the database instance is yielded to it, and the
# transaction is committed when the block terminates. If the block
# raises an exception, a rollback will be performed instead. Note that if
# a block is given, #commit and #rollback should never be called
# explicitly or you'll get an error when the block terminates.
#
# If a block is not given, it is the caller's responsibility to end the
# transaction explicitly, either by calling #commit, or by calling
# #rollback.
def transaction(mode = :deferred)
execute "begin #{mode.to_s} transaction"
@transaction_active = true
if block_given?
abort = false
begin
yield self
rescue ::Object
abort = true
raise
ensure
abort and rollback or commit
end
end
true
end
# Commits the current transaction. If there is no current transaction,
# this will cause an error to be raised. This returns +true+, in order
# to allow it to be used in idioms like
# <tt>abort? and rollback or commit</tt>.
def commit
execute "commit transaction"
@transaction_active = false
true
end
# Rolls the current transaction back. If there is no current transaction,
# this will cause an error to be raised. This returns +true+, in order
# to allow it to be used in idioms like
# <tt>abort? and rollback or commit</tt>.
def rollback
execute "rollback transaction"
@transaction_active = false
true
end
# Returns +true+ if there is a transaction active, and +false+ otherwise.
def transaction_active?
@transaction_active
end
private
# Loads the corresponding driver, or if it is nil, attempts to locate a
# suitable driver.
def load_driver(driver)
case driver
when Class
# do nothing--use what was given
when Symbol, String
require "sqlite3/driver/#{driver.to_s.downcase}/driver"
driver = SQLite3::Driver.const_get(driver)::Driver
else
["FFI"].each do |d|
begin
require "sqlite3/driver/#{d.downcase}/driver"
driver = SQLite3::Driver.const_get(d)::Driver
break
rescue SyntaxError
raise
rescue ScriptError, Exception, NameError
end
end
raise "no driver for sqlite3 found" unless driver
end
@driver = driver.new
end
end
end