Refactor connection handler

ConnectionHandler will not have any knowlodge of AR models now, it will
only know about the specs.
Like that we can decouple the two, and allow the same model to use more
than one connection.

Historically, folks used to create abstract AR classes on the fly in
order to have multiple connections for the same model, and override the
connection methods.

With this, now we can override the `specificiation_id` method in the
model, to return a key, that will be used to find the connection_pool
from the handler.

1 files changed, 27 insertions, 7 deletions

diff --git a/activerecord/lib/active_record/connection_handling.rb b/activerecord/lib/active_record/connection_handling.rb
index a8b3d03ba5..c54b8adc4e 100644
--- a/activerecord/lib/active_record/connection_handling.rb
+++ b/activerecord/lib/active_record/connection_handling.rb
@@ -45,16 +45,19 @@ module ActiveRecord
     # The exceptions AdapterNotSpecified, AdapterNotFound and +ArgumentError+
     # may be returned on an error.
     def establish_connection(spec = nil)
+      raise RuntimeError, "Anonymous class is not allowed." unless name
+
       spec     ||= DEFAULT_ENV.call.to_sym
       resolver =   ConnectionAdapters::ConnectionSpecification::Resolver.new configurations
-      spec     =   resolver.spec(spec)
+      spec     =   resolver.spec(spec, self == Base ? "primary" : name)
+      self.specification_id = spec.id
 
       unless respond_to?(spec.adapter_method)
         raise AdapterNotFound, "database configuration specifies nonexistent #{spec.config[:adapter]} adapter"
       end
 
       remove_connection
-      connection_handler.establish_connection self, spec
+      connection_handler.establish_connection spec
     end
 
     class MergeAndResolveDefaultUrlConfig # :nodoc:
@@ -87,6 +90,23 @@ module ActiveRecord
       retrieve_connection
     end
 
+    def specification_id=(value)
+      @specification_id = value
+    end
+
+    def specification_id(fallback = true)
+      return @specification_id if defined?(@specification_id)
+      find_legacy_spec_id(self) if fallback
+    end
+
+    def find_legacy_spec_id(klass)
+      return "primary" if klass == Base
+      if id = klass.specification_id(false)
+        return id
+      end
+      find_legacy_spec_id(klass.superclass)
+    end
+
     def connection_id
       ActiveRecord::RuntimeRegistry.connection_id ||= Thread.current.object_id
     end
@@ -106,20 +126,20 @@ module ActiveRecord
     end
 
     def connection_pool
-      connection_handler.retrieve_connection_pool(self) or raise ConnectionNotEstablished
+      connection_handler.retrieve_connection_pool(specification_id) or raise ConnectionNotEstablished
     end
 
     def retrieve_connection
-      connection_handler.retrieve_connection(self)
+      connection_handler.retrieve_connection(specification_id)
     end
 
     # Returns +true+ if Active Record is connected.
     def connected?
-      connection_handler.connected?(self)
+      connection_handler.connected?(specification_id)
     end
 
-    def remove_connection(klass = self)
-      connection_handler.remove_connection(klass)
+    def remove_connection(id = specification_id)
+      connection_handler.remove_connection(id)
     end
 
     def clear_cache! # :nodoc: