module SQLite3

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 abort? and rollback or commit.

# File lib/sqlite3/database.rb, line 505
def commit
  execute "commit transaction"
  true
end

This is another approach to creating an aggregate function (see create_aggregate). Instead of explicitly specifying the name, callbacks, arity, and type, you specify a factory object (the “handler”) that knows how to obtain all of that information. The handler should respond to the following messages:

arity

corresponds to the arity parameter of create_aggregate. This message is optional, and if the handler does not respond to it, the function will have an arity of -1.

name

this is the name of the function. The handler must implement this message.

new

this must be implemented by the handler. It should return a new instance of the object that will handle a specific invocation of the function.

The handler instance (the object returned by the new message, described above), must respond to the following messages:

step

this is the method that will be called for each step of the aggregate function's evaluation. It should implement the same signature as the step callback for create_aggregate.

finalize

this is the method that will be called to finalize the aggregate function's evaluation. It should implement the same signature as the finalize callback for create_aggregate.

Example:

class LengthsAggregateHandler
  def self.arity; 1; end

  def initialize
    @total = 0
  end

  def step( ctx, name )
    @total += ( name ? name.length : 0 )
  end

  def finalize( ctx )
    ctx.result = @total
  end
end

db.create_aggregate_handler( LengthsAggregateHandler )
puts db.get_first_value( "select lengths(name) from A" )

# File lib/sqlite3/database.rb, line 447
def create_aggregate_handler( handler )
  proxy = Class.new do
    def initialize handler
      @handler  = handler
      @fp       = FunctionProxy.new
    end

    def step( *args )
      @handler.step(@fp, *args)
    end

    def finalize
      @handler.finalize @fp
      @fp.result
    end
  end
  define_aggregator(handler.name, proxy.new(handler.new))
  self
end

Returns true if the database has been open in readonly mode A helper to check before performing any operation

# File lib/sqlite3/database.rb, line 521
def readonly?
  @readonly
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 abort? and rollback or commit.

# File lib/sqlite3/database.rb, line 514
def rollback
  execute "rollback transaction"
  true
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 :deferred (the default), :immediate, or :exclusive.

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.

# File lib/sqlite3/database.rb, line 483
def transaction( mode = :deferred )
  execute "begin #{mode.to_s} transaction"

  if block_given?
    abort = false
    begin
      yield self
    rescue ::Object
      abort = true
      raise
    ensure
      abort and rollback or commit
    end
  end

  true
end