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:
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:
Don't commit config/database.yml
We don't commit config/database.yml in a git repository. There are two reasons
for this.
- We don't want to disclose database password information of the committer.
- 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:
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:
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.