From 8d32346cdec04dd85ab682eeb9f4edfcd0c9ccef Mon Sep 17 00:00:00 2001
From: Eileen Uchitelle <eileencodes@gmail.com>
Date: Fri, 1 Feb 2019 11:33:48 -0500
Subject: Add ability to change the names of the default handlers

When I wrote the `connected_to` and `connects_to` API's I wrote them
with the idea in mind that it didn't really matter what the
handlers/roles were called as long as those connecting to the roles knew
which one wrote and which one read.

With the introduction of the middleware Rails begins to assume it's
`writing` and `reading` and there's no room for other roles. At GitHub
we've been using this method for a long time so we have a ton of legacy
code that uses different handler names `default` and `readonly`. We
could rename all our code but I think this is better for a few reasons:

- Legacy apps that have been using multiple databases for a long time
  can have an eaiser time switching.
- If we later find this to cause more issues than it's worth we can
  easily deprecate.
- We won't force old apps to rewrite the resolver middleware just to use
  a different handler.

Adding the writing_role/reading_role required that I move the code that
creates the first handler for writing to the railtie. If I didn't move
this the core class would assign the handler before I was able to assign
a new one in my configuration and I'd end up with 3 handlers instead of
2.
---
 activerecord/lib/active_record/core.rb                              | 5 ++++-
 .../lib/active_record/middleware/database_selector/resolver.rb      | 6 +++---
 activerecord/lib/active_record/railtie.rb                           | 1 +
 3 files changed, 8 insertions(+), 4 deletions(-)

(limited to 'activerecord/lib')

diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 519acd7605..84604452f7 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -125,6 +125,10 @@ module ActiveRecord
 
       mattr_accessor :connection_handlers, instance_accessor: false, default: {}
 
+      mattr_accessor :writing_role, instance_accessor: false, default: :writing
+
+      mattr_accessor :reading_role, instance_accessor: false, default: :reading
+
       class_attribute :default_connection_handler, instance_writer: false
 
       self.filter_attributes = []
@@ -138,7 +142,6 @@ module ActiveRecord
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new
-      self.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
     end
 
     module ClassMethods
diff --git a/activerecord/lib/active_record/middleware/database_selector/resolver.rb b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
index acdb9b3238..fc71835cea 100644
--- a/activerecord/lib/active_record/middleware/database_selector/resolver.rb
+++ b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
@@ -45,7 +45,7 @@ module ActiveRecord
 
           def read_from_primary(&blk)
             ActiveRecord::Base.connection.while_preventing_writes do
-              ActiveRecord::Base.connected_to(role: :writing) do
+              ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
                 instrumenter.instrument("database_selector.active_record.read_from_primary") do
                   yield
                 end
@@ -54,7 +54,7 @@ module ActiveRecord
           end
 
           def read_from_replica(&blk)
-            ActiveRecord::Base.connected_to(role: :reading) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.reading_role) do
               instrumenter.instrument("database_selector.active_record.read_from_replica") do
                 yield
               end
@@ -62,7 +62,7 @@ module ActiveRecord
           end
 
           def write_to_primary(&blk)
-            ActiveRecord::Base.connected_to(role: :writing) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
               instrumenter.instrument("database_selector.active_record.wrote_to_primary") do
                 yield
               ensure
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index a981fa97d9..f0b5ab2f08 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -197,6 +197,7 @@ end_error
     # and then establishes the connection.
     initializer "active_record.initialize_database" do
       ActiveSupport.on_load(:active_record) do
+        self.connection_handlers = { writing_role => ActiveRecord::Base.default_connection_handler }
         self.configurations = Rails.application.config.database_configuration
         establish_connection
       end
-- 
cgit v1.2.3