Class: SqlPostgres::Cursor

Inherits:
Object
  • Object
show all
Defined in:
lib/sqlpostgres/Cursor.rb

Overview

This class creates and manages a cursor.

Example: ** example: cursor

Transaction.new(connection) do
  select = Select.new(connection)
  select.select('i')
  select.from('foo')
  Cursor.new('my_cursor', select, {}, connection) do |cursor|
    while !(rows = cursor.fetch).empty?
      for row in rows
        p row # {"i"=>0}
              # {"i"=>1}
              # {"i"=>2}
              # {"i"=>3}
              # {"i"=>4}
        end
    end
  end
end

**

Fetching a single row at a time, the default for fetch, is slow. Usually you will want to speed things up by calling, for example, fetch(1000).

Instance Method Summary collapse

Constructor Details

#initialize(name, select, opts = {}, connection = Connection.default) ⇒ Cursor

Create a cursor. If a block is given, yield the cursor to the block, closing the cursor when the block returns, and returning results of the block.

If no connection is given, then the default connection is used.

name

The cursor’s name

select

a Select statement

opts

Options hash. Keys are:

:scroll=>(boolean)    If true, create a SCROLL cursor.  If false,
                      create a NO SCROLL cursor.  If not specified,
                      the default is to allow scrolling in cases
                      where performance will not suffer.
:hold=>(boolean)      If true, create a WITH HOLD cursor.  If
                      false, create a HOLD cursor.  WITHOUT HOLD
                      is the default.  A HOLD cursor can be used
                      outside of the transaction that created it.
connection

The database connection



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# File 'lib/sqlpostgres/Cursor.rb', line 54

def initialize(name, select, opts = {}, connection = Connection.default)
  if block_given?
    cursor = self.class.new(name, select, opts, connection)
    result = yield(cursor)
    cursor.close
    result
  else
    @name = name
    @select = select
    @opts = opts
    @connection = connection
    declare_cursor
  end
end

Instance Method Details

#close ⇒ Object

Close the cursor. Once closed, it may not be closed or fetched from again.



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# File 'lib/sqlpostgres/Cursor.rb', line 107

def close
  statement = "close #{@name}"
  @connection.exec(statement)
end

#fetch(direction = 'NEXT') ⇒ Object

Fetch a row or rows from the cursor.

direction

A string specifying which row or rows to fetch. See the postgres documentation for the “DECLARE” statement.

NEXT
PRIOR
FIRST
LAST
ABSOLUTE count
RELATIVE count
count
ALL
FORWARD
FORWARD count
FORWARD ALL
BACKWARD
BACKWARD count
BACKWARD ALL



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# File 'lib/sqlpostgres/Cursor.rb', line 89

def fetch(direction = 'NEXT')
  @select.fetch_by_cursor(@name, direction, @connection)
end

#move(direction = 'NEXT') ⇒ Object

Seek a cursor. Works exactly the same (and takes the same arguments) as fetch, but returns no rows.

direction

See #fetch



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# File 'lib/sqlpostgres/Cursor.rb', line 99

def move(direction = 'NEXT')
  statement = "move #{direction} from #{@name}"
  @connection.exec(statement)
end