How to get access to Hanami connection instance

Question

Hanami uses Sequel as default ORM

There are different plugins for Sequel

Sometimes to use it you need to access to database connection object

For example to use PostgreSQL advisory locking for mutexes

There are such gems for this: sequel-advisory-locking, sequel-pg_advisory_lock

First, you should load an extension for Sequel::Database instance

DB.extension(:advisory_locking)

Then use it in your app like this

DB.advisory_lock('my_key') do
  # do stuff with lock
end

But there is problem to use such libraries with Hanami

There is no information about it in official guide

On database configuration page such info:

Hanami models use ROM as a low-level backend. This means that you can easily use any Sequel plugins in your app. For this you need to define a gateway block in your model configuration, add the extension by calling extension on gateway.connection and pass the extension name in:

# config/environment.rb
Hanami.configure do
  model do
    gateway do |g|
      g.connection.extension(:connection_validator)
    end
  end
end

What I tried is define constant in this config

Hanami.configure do
  model do
    gateway do |g|
      DB = g.connection

      DB.extension(:connection_validator)
      DB.extension(:advisory_locking)
    end
  end
end

And then use this DB somewhere in the app, for example as DB.advisory_lock('my_key') { do_stuff_with_lock }

But such constants define within a block looks not good

How to get connection instance in Hanami app?

Answer 1

There is config object in Hanami -- Hanami::Model.configuration

In fact it is the getter for @configuration instance variable

It is instance of Hanami::Model::Configuration and has such instance variables like @url, @entities, @logger and others. So it's possible to call getters to get them

It also has connection method. This method returns gateway.connection

And this gateway.connection is just what is needed. This is exactly the instance of connection to the database, on which you can call methods

For example

Hanami::Model.configuration.connection.advisory_lock('my_lock') do
  # do stuff with lock
end

I want to note that all these methods are indicated by the comment # @api private. It means that their implementation may be changed in future versions.