Add DatabaseConfig Struct and associated methods

Passing around and parsing hashes is easy if you know that it's a two
tier config and each key will be named after the environment and each
value will be the config for that environment key.

This falls apart pretty quickly with three-tier configs. We have no idea
what the second tier will be named (we know the first is primary but we
don't know the second), we have no easy way of figuring out
how deep a hash we have without iterating over it, and we'd have to do
this a lot throughout the code since it breaks all of Active Record's
assumptions regarding configurations.

These methods allow us to pass around objects instead. This will allow
us to more easily parse the configs for the rake tasks. Evenually I'd
like to replace the Active Record connection management that passes
around config hashes to use these methods as well but that's much
farther down the road.

`walk_configs` takes an environment, specification name, and a config
and turns them into DatabaseConfig struct objects so we can ask the
configs questions like:

```
db_config.spec_name
=> animals

db_config.env_name
=> development

db_config.config
{ :adapter => mysql etc }
```

`db_configs` loops through all given configurations and returns an array
of DatabaseConfig structs for each config in the yaml file.

and lastly `configs_for` takes an environment and either returns the
spec name and config if a block is given or returns an array of
DatabaseConfig structs just for the given environment.

1 files changed, 39 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index e1a0b2ecf8..b6b4c76569 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -60,6 +60,45 @@ module ActiveRecord
         @@configurations
       end
 
+      DatabaseConfig = Struct.new(:env_name, :spec_name, :config) # :nodoc
+
+      # Given an env, spec and config creates DatabaseConfig structs with
+      # each attribute set.
+      def self.walk_configs(env_name, spec_name, config) # :nodoc:
+        if config["database"] || env_name == "default"
+          DatabaseConfig.new(env_name, spec_name, config)
+        else
+          config.each_pair.map do |spec_name, sub_config|
+            walk_configs(env_name, spec_name, sub_config)
+          end
+        end
+      end
+
+      # Walks all the configs passed in and returns an array
+      # of DatabaseConfig structs for each configuration.
+      def self.db_configs(configs = configurations) # :nodoc:
+        configs.each_pair.flat_map do |env_name, config|
+          walk_configs(env_name, "primary", config)
+        end
+      end
+
+      # Collects the configs for the environment passed in.
+      #
+      # If a block is given returns the specification name and configuration
+      # otherwise returns an array of DatabaseConfig structs for the environment.
+      def self.configs_for(environment, configs = configurations, &blk) # :nodoc:
+        env_with_configs = db_configs(configs).select do |db_config|
+          db_config.env_name == environment
+        end
+
+        if block_given?
+          env_with_configs.each do |env_with_config|
+            yield env_with_config.spec_name, env_with_config.config
+          end
+        else
+          env_with_configs
+        end
+      end
       ##
       # :singleton-method:
       # Determines whether to use Time.utc (using :utc) or Time.local (using :local) when pulling