class Pgtk::Pool

Pool.

Author

Yegor Bugayenko (yegor256@gmail.com)

Copyright

Copyright © 2019 Yegor Bugayenko

License

MIT

Public Class Methods

new(wire, log: Loog::NULL) click to toggle source

Constructor.

# File lib/pgtk/pool.rb, line 34
def initialize(wire, log: Loog::NULL)
  @wire = wire
  @log = log
  @pool = Queue.new
end

Public Instance Methods

exec(query, args = [], result = 0) { |res| ... } click to toggle source

Make a query and return the result as an array of hashes. For example, in order to fetch the list of all books belonging to the user:

books = pool.exec('SELECT * FROM book WHERE owner = $1', ['yegor256'])
books.each do |row|
  puts 'ID: ' + row['id'].to_i
  puts 'Created: ' + Time.parse(row['created'])
  puts 'Title: ' + row['title']
end

All values in the retrieved hash are strings. No matter what types of of data you have in the database, you get strings here. It's your job to convert them to the type you need.

In order to insert a new row (pay attention to the RETURNING clause at the end of the SQL query):

id = pool.exec(
  'INSERT INTO book (owner, title) VALUES ($1, $2) RETURNING id',
  ['yegor256', 'Elegant Objects']
)[0]['id'].to_i

You can also pass a block to this method, if you want to get an instance of PG::Result instead of an array of hashes:

pool.exec('SELECT * FROM book WHERE owner = $1', ['yegor256']) do |res|
  res.each do |row|
    puts 'ID: ' + row['id'].to_i
    puts 'Title: ' + row['title']
  end
end

When the query is too long it's convenient to use an array to specify it:

pool.exec(
  [
    'SELECT * FROM book',
    'LEFT JOIN user ON user.id = book.owner',
    'WHERE user.login = $1 AND book.title = $2'
  ],
  ['yegor256', 'Elegant Objects']
)

More details about exec_params, which is called here, you can find here: www.rubydoc.info/gems/pg/0.17.1/PG%2FConnection:exec_params

# File lib/pgtk/pool.rb, line 104
def exec(query, args = [], result = 0)
  connect do |c|
    t = Txn.new(c, @log)
    if block_given?
      t.exec(query, args, result) do |res|
        yield res
      end
    else
      t.exec(query, args, result)
    end
  end
end
start(max = 8) click to toggle source

Start it with a fixed number of connections. The amount of connections is specified in max argument and should be big enough to handle the amount of parallel connections you may have to the database. However, keep in mind that not all servers will allow you to have many connections open at the same time. For example, Heroku free PostgreSQL database allows only one connection open.

# File lib/pgtk/pool.rb, line 51
def start(max = 8)
  max.times do
    @pool << @wire.connection
  end
  @log.debug("PostgreSQL pool started with #{max} connections")
  self
end
transaction() { |t| ... } click to toggle source

Run a transaction. The block has to be provided. It will receive a temporary object, which implements method exec, which works exactly like the method exec of class Pool, for example:

pgsql.transaction do |t|
  t.exec('DELETE FROM user WHERE id = $1', [id])
  t.exec('INSERT INTO user (name) VALUES ($1)', [name])
end
# File lib/pgtk/pool.rb, line 125
def transaction
  connect do |c|
    t = Txn.new(c, @log)
    yield t
  end
end
version() click to toggle source

Get the version of PostgreSQL server.

# File lib/pgtk/pool.rb, line 41
def version
  @version ||= exec('SHOW server_version')[0]['server_version'].split(' ')[0]
end

Private Instance Methods

connect() { |conn| ... } click to toggle source
# File lib/pgtk/pool.rb, line 163
def connect
  conn = @pool.pop
  begin
    yield conn
  rescue StandardError => e
    conn.close unless conn.finished?
    conn = @wire.connection
    raise e
  ensure
    @pool << conn
  end
end