class Pgtk::Pool
Pool
.
- Author
-
Yegor Bugayenko (yegor256@gmail.com)
- Copyright
-
Copyright © 2019 Yegor Bugayenko
- License
-
MIT
Public Class Methods
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
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 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
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
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
# 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