fix(multidb): allow associations across databases to work properly (#572)

Author: SteveBunlon

app/services/forest_liana/base_getter.rb

@@ -32,15 +32,23 @@ def compute_includes
 
     def optimize_record_loading(resource, records)
       instance_dependent_associations = instance_dependent_associations(resource)
-      eager_loads = @includes - instance_dependent_associations
 
-      result = records.eager_load(eager_loads)
+      preload_loads = @includes.select do |name|
+        targetModelConnection = resource.reflect_on_association(name).inverse_of&.active_record&.connection
+        targetModelDatabase = targetModelConnection.current_database if targetModelConnection.respond_to? :current_database
+        resourceConnection = resource.connection
+        resourceDatabase = resourceConnection if resourceConnection.respond_to? :current_database
+
+        targetModelDatabase != resourceDatabase
+      end + instance_dependent_associations
+
+      result = records.eager_load(@includes - preload_loads)
 
       # Rails 7 can mix `eager_load` and `preload` in the same scope
       # Rails 6 cannot mix `eager_load` and `preload` in the same scope
       # Rails 6 and 7 cannot mix `eager_load` and `includes` in the same scope
       if Rails::VERSION::MAJOR >= 7
-        result = result.preload(instance_dependent_associations)
+        result = result.preload(preload_loads)
       end
 
       result

spec/dummy/app/models/car.rb

@@ -0,0 +1,3 @@
+class Car < GarageRecord
+  belongs_to :driver
+end

spec/dummy/app/models/driver.rb

@@ -0,0 +1,3 @@
+class Driver < UserRecord
+  has_one :car
+end

spec/dummy/app/models/garage_record.rb

@@ -0,0 +1,4 @@
+class GarageRecord < ApplicationRecord
+  self.abstract_class = true
+  connects_to database: { writing: :garage, reading: :garage }
+end

spec/dummy/app/models/user_record.rb

@@ -0,0 +1,4 @@
+class UserRecord < ApplicationRecord
+  self.abstract_class = true
+  connects_to database: { writing: :user, reading: :user }
+end

spec/dummy/config/database.yml

@@ -19,6 +19,13 @@ development:
 test:
   <<: *default
   database: db/test.sqlite3
+  
+garage:
+  <<: *default
+  database: db/test2.sqlite3
+user:
+  <<: *default
+  database: db/test3.sqlite3
 
 production:
   <<: *default

spec/dummy/db/migrate/20220719094127_create_cars.rb

@@ -0,0 +1,8 @@
+class CreateCars < ActiveRecord::Migration[6.0]
+  def change
+    Car.connection.create_table :cars do |t|
+      t.string :model
+      t.references :driver, index: true
+    end
+  end
+end

spec/dummy/db/migrate/20220719094450_create_drivers.rb

@@ -0,0 +1,7 @@
+class CreateDrivers < ActiveRecord::Migration[6.0]
+  def change
+    Driver.connection.create_table :drivers do |t|
+      t.string :firstname
+    end
+  end
+end

spec/lib/forest_liana/bootstrapper_spec.rb

@@ -30,7 +30,9 @@ module ForestLiana
           Reference,
           Town,
           Tree,
-          User
+          User,
+          Driver,
+          Car,
         ]
       end