Move the `from` bind logic to a `FromClause` class

Contrary to my previous commit message, it wasn't overkill, and led to
much cleaner code.

[Sean Griffin & anthonynavarre]

1 files changed, 32 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation/from_clause.rb b/activerecord/lib/active_record/relation/from_clause.rb
new file mode 100644
index 0000000000..fc16ac58b4
--- /dev/null
+++ b/activerecord/lib/active_record/relation/from_clause.rb
@@ -0,0 +1,32 @@
+module ActiveRecord
+  class Relation
+    class FromClause
+      attr_reader :value, :name
+
+      def initialize(value, name)
+        @value = value
+        @name = name
+      end
+
+      def binds
+        if value.is_a?(Relation)
+          value.arel.bind_values + value.bind_values
+        else
+          []
+        end
+      end
+
+      def merge(other)
+        self
+      end
+
+      def empty?
+        value.nil?
+      end
+
+      def self.empty
+        new(nil, nil)
+      end
+    end
+  end
+end