decouple the factory method from the constructing model

The factory method only requires the constructing model to get the
connection object. Since the model is available when calling the factory
method, we can just pass the appropriate connection in.

activerecord/lib/active_record/core.rb

@@ -135,7 +135,7 @@ module ActiveRecord
         key = primary_key
 
         s = find_by_statement_cache[key] || find_by_statement_cache.synchronize {
-          find_by_statement_cache[key] ||= StatementCache.create { |params|
+          find_by_statement_cache[key] ||= StatementCache.create(connection) { |params|
             where(key => params[key]).limit(1)
           }
         }
@@ -159,7 +159,7 @@ module ActiveRecord
 
         klass = self
         s = find_by_statement_cache[key] || find_by_statement_cache.synchronize {
-          find_by_statement_cache[key] ||= StatementCache.create { |params|
+          find_by_statement_cache[key] ||= StatementCache.create(connection) { |params|
             wheres = key.each_with_object({}) { |param,o|
               o[param] = params[param]
             }

activerecord/lib/active_record/statement_cache.rb

@@ -76,11 +76,9 @@ module ActiveRecord
 
     attr_reader :bind_map, :query_builder
 
-    def self.create(block = Proc.new)
+    def self.create(connection, block = Proc.new)
       relation      = block.call Params.new
       bind_map      = BindMap.new relation.bind_values
-      klass         = relation.klass
-      connection    = klass.connection
       query_builder = connection.cacheable_query relation.arel
       new query_builder, bind_map
     end

activerecord/test/cases/statement_cache_test.rb

@@ -15,7 +15,7 @@ module ActiveRecord
       Book.create(name: "my book")
       Book.create(name: "my other book")
 
-      cache = StatementCache.create do |params|
+      cache = StatementCache.create(Book.connection) do |params|
         Book.where(:name => params[:name])
       end
 
@@ -30,7 +30,7 @@ module ActiveRecord
       b1 = Book.create(name: "my book")
       b2 = Book.create(name: "my other book")
 
-      cache = StatementCache.create do |params|
+      cache = StatementCache.create(Book.connection) do |params|
         Book.where(id: params[:id])
       end
 
@@ -53,7 +53,7 @@ module ActiveRecord
     #End
 
     def test_statement_cache_with_simple_statement
-      cache = ActiveRecord::StatementCache.create do |params|
+      cache = ActiveRecord::StatementCache.create(Book.connection) do |params|
         Book.where(name: "my book").where("author_id > 3")
       end
 
@@ -64,7 +64,7 @@ module ActiveRecord
     end
 
     def test_statement_cache_with_complex_statement
-      cache = ActiveRecord::StatementCache.create do |params|
+      cache = ActiveRecord::StatementCache.create(Book.connection) do |params|
         Liquid.joins(:molecules => :electrons).where('molecules.name' => 'dioxane', 'electrons.name' => 'lepton')
       end
 
@@ -77,7 +77,7 @@ module ActiveRecord
     end
 
     def test_statement_cache_values_differ
-      cache = ActiveRecord::StatementCache.create do |params|
+      cache = ActiveRecord::StatementCache.create(Book.connection) do |params|
         Book.where(name: "my book")
       end