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    Configuring and connecting to a database

    There are two ways to connect to a database in a Rails application.

    Using only an environment variable

    Ruby on Rails support environment variables out of the box. Sometimes, we can't commit some configurations to a repository. In such cases we use environment variables.

    We can set DATABASE_URL environment variable to connect to a particular database. In platforms like heroku and all, they provide us with the option to explicitly set these env variables, within their dashboards itself. The following is an example of how the database URL for connecting to a postgresql adapter would look like:

    1ENV['DATABASE_URL'] # => "postgresql://localhost/granite_development?pool=5"

    This method is not used in the development environment. Though this can be useful in production and heroku environment. In development, we use config/database.yml.

    Using database.yml

    We can specify all the database connection details in config/database.yml file. Using following snippet, a Rails application can connect to a Postgres database:

    1development:
    2  adapter: postgresql
    3  database: granite_development
    4  pool: 5
    5  username: postgres
    6  password: YourPostgresPassword

    Don't commit config/database.yml

    We don't commit config/database.yml in a git repository. There are two reasons for this.

    1. We don't want to disclose database password information of the committer.
    2. Every developer's database details can be different i.e. username and password. Every time we push the code, there will be a conflict in a file.

    If config/database.yml is missing

    As mentioned config/database.yml is not pushed to the repository. So when we clone a new repository, this file will be missing.

    Generally, a Rails application will have a config/database.yml.example or a config/database.yml.postgresql file.

    We can copy the content of any of these files into a new file named config/database.yml, so as make connection with pg gem:

    1cp config/database.yml.postgresql config/database.yml

    If no example file is present, you can copy content from the example database.yml for your application's database.

    Config options

    We can check selected database's connection config with ActiveRecord::Base.connection_config. We might need to configure more options. Now, let's try to understand some of the common database config options:

    1host - Defaults to "localhost". This can also be a remote database URL.
    2port - Port number, Defaults to 5432 for postgres.
    3username - Username of the database.
    4password - Password for the database.
    5database - The name of the database.
    6encoding - (Optional) Sets the client encoding.
    7connect_timeout - The timeout to establish a new connection to the database before failing.
    8read_timeout - The time to receive data after connected.
    9pool - Maximum number of connections to database per application.
    10  Defaults to 5.
    11  e.g. 2 * 16 (puma) + 1 * 10 (sidekiq) = 42
    12  here, 2 - puma processes, each process has 16 threads
    13        1 - sidekiq process, each process has 10 threads

    Connection preference

    In case, we use both config/database.yml and ENV['DATABASE_URL'] then configuration will be merged together. Please refer Rails guides for the merge strategy.

    There is nothing to commit in this chapter since we have intentionally specified config/database.yml as untracked using the .gitignore file.

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