Add fallback mode for development mode and similar.

README.markdown

@@ -119,6 +119,23 @@ Note that the symbol `:default` will (unless you override it) refer to the defau
 top-level ActiveRecord configuration.
 
 
+Development mode
+================
+
+In development you will typically want `Multidb.use(:slave)` to still work, but you
+probably don't want to run multiple databases on your development box. To make `use`
+silently fall back to using the default connection, simply set `fallback: true` in
+`database.yml`:
+
+    production:
+      adapter: postgresql
+      database: myapp_production
+      username: ohoh
+      password: mymy
+      host: db1
+      multidb:
+        fallback: true
+
 Legal
 =====
 

lib/multidb.rb

@@ -11,8 +11,8 @@ def install!
         ActiveRecord::Base.class_eval do
           include Multidb::ModelExtensions
         end
-        @balancer = Balancer.new(@configuration)
       end
+      @balancer = Balancer.new(@configuration)
     end
 
     attr_reader :balancer

lib/multidb/balancer.rb

@@ -30,23 +30,31 @@ class Balancer
     def initialize(configuration)
       @candidates = {}.with_indifferent_access
       @configuration = configuration
-      @configuration.raw_configuration[:databases].each_pair do |name, config|
+      (@configuration.raw_configuration[:databases] || {}).each_pair do |name, config|
         configs = config.is_a?(Array) ? config : [config]
         configs.each do |config|          
           candidate = Candidate.new(@configuration.default_adapter.merge(config))
           @candidates[name] ||= []
           @candidates[name].push(candidate)
         end
       end
+      if @configuration.raw_configuration.include?(:fallback)
+        @fallback = @configuration.raw_configuration[:fallback]
+      elsif defined?(Rails)
+        @fallback = %w(development test).include?(Rails.env)
+      else
+        @fallback = false
+      end
       @default_candidate = Candidate.new(@configuration.default_pool)
       unless @candidates.include?(:default)
         @candidates[:default] = [@default_candidate]
       end
     end
 
     def get(name, &block)
-      candidates = @candidates[name] || []
-      raise ArgumentError, "No such database connection '#{name}'" if candidates.blank?
+      candidates = @candidates[name]
+      candidates ||= @fallback ? @candidates[:default] : []
+      raise ArgumentError, "No such database connection '#{name}'" if candidates.empty?
       candidate = candidates.respond_to?(:sample) ? 
         candidates.sample : candidates[rand(candidates.length)]
       block_given? ? yield(candidate) : candidate