Allow "url" sub key in database.yml configuration

Currently a developer can pass in a YAML configuration that fully specifies connection information:

```
production:
  database: triage_production
  adapter: password
  pool: 5
```

They can also pass in a string that specifies a connection URL directly to an environment key:

```
production: postgresql://localhost/foo
```

This PR allows the use of both a connection url and specifying connection attributes via YAML through the use of the "url" sub key:

```
production:
  url: postgresql://localhost/foo
  pool: 3
```

This will allow developers to inherit Active Record options such as `pool` from `&defaults` and still use a secure connection url such as `<%= ENV['DATABASE_URL'] %>`. The URL is expanded into a hash and then merged back into the YAML hash. If there are any conflicts, the values from the connection URL are preferred. 

Talked this over with @josevalim

1 files changed, 8 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
index bea9a22442..049768effc 100644
--- a/activerecord/lib/active_record/connection_adapters/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
@@ -223,7 +223,15 @@ module ActiveRecord
           end
         end
 
+        # Accepts a hash. Expands the "url" key that contains a
+        # URL database connection to a full connection
+        # hash and merges with the rest of the hash.
+        # Connection details inside of the "url" key win any merge conflicts
         def resolve_hash_connection(spec)
+          if url = spec.delete("url")
+            connection_hash = resolve_string_connection(url)
+            spec.merge!(connection_hash)
+          end
           spec
         end