1 files changed, 133 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
new file mode 100644
index 0000000000..8b9ba3e633
--- /dev/null
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -0,0 +1,133 @@
+module ActiveRecord
+  class Relation
+    class WhereClause # :nodoc:
+      attr_reader :predicates, :binds
+
+      delegate :any?, :empty?, to: :predicates
+
+      def initialize(predicates, binds)
+        @predicates = predicates
+        @binds = binds
+      end
+
+      def +(other)
+        WhereClause.new(
+          predicates + other.predicates,
+          binds + other.binds,
+        )
+      end
+
+      def merge(other)
+        WhereClause.new(
+          predicates_unreferenced_by(other) + other.predicates,
+          non_conflicting_binds(other) + other.binds,
+        )
+      end
+
+      def except(*columns)
+        WhereClause.new(
+          predicates_except(columns),
+          binds_except(columns),
+        )
+      end
+
+      def to_h(table_name = nil)
+        equalities = predicates.grep(Arel::Nodes::Equality)
+        if table_name
+          equalities = equalities.select do |node|
+            node.left.relation.name == table_name
+          end
+        end
+
+        binds = self.binds.select(&:first).to_h.transform_keys(&:name)
+
+        equalities.map { |node|
+          name = node.left.name
+          [name, binds.fetch(name.to_s) {
+            case node.right
+            when Array then node.right.map(&:val)
+            when Arel::Nodes::Casted, Arel::Nodes::Quoted
+              node.right.val
+            end
+          }]
+        }.to_h
+      end
+
+      def ==(other)
+        other.is_a?(WhereClause) &&
+          predicates == other.predicates &&
+          binds == other.binds
+      end
+
+      def invert
+        WhereClause.new(inverted_predicates, binds)
+      end
+
+      def self.empty
+        new([], [])
+      end
+
+      protected
+
+      def referenced_columns
+        @referenced_columns ||= begin
+          equality_nodes = predicates.select { |n| equality_node?(n) }
+          Set.new(equality_nodes, &:left)
+        end
+      end
+
+      private
+
+      def predicates_unreferenced_by(other)
+        predicates.reject do |n|
+          equality_node?(n) && other.referenced_columns.include?(n.left)
+        end
+      end
+
+      def equality_node?(node)
+        node.respond_to?(:operator) && node.operator == :==
+      end
+
+      def non_conflicting_binds(other)
+        conflicts = referenced_columns & other.referenced_columns
+        conflicts.map! { |node| node.name.to_s }
+        binds.reject { |col, _| conflicts.include?(col.name) }
+      end
+
+      def inverted_predicates
+        predicates.map { |node| invert_predicate(node) }
+      end
+
+      def invert_predicate(node)
+        case node
+        when NilClass
+          raise ArgumentError, 'Invalid argument for .where.not(), got nil.'
+        when Arel::Nodes::In
+          Arel::Nodes::NotIn.new(node.left, node.right)
+        when Arel::Nodes::Equality
+          Arel::Nodes::NotEqual.new(node.left, node.right)
+        when String
+          Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(node))
+        else
+          Arel::Nodes::Not.new(node)
+        end
+      end
+
+      def predicates_except(columns)
+        predicates.reject do |node|
+          case node
+          when Arel::Nodes::Between, Arel::Nodes::In, Arel::Nodes::NotIn, Arel::Nodes::Equality, Arel::Nodes::NotEqual, Arel::Nodes::LessThanOrEqual, Arel::Nodes::GreaterThanOrEqual
+            subrelation = (node.left.kind_of?(Arel::Attributes::Attribute) ? node.left : node.right)
+            columns.include?(subrelation.name.to_s)
+          end
+        end
+      end
+
+      def binds_except(columns)
+        binds.reject do |column, _|
+          columns.include?(column.name)
+        end
+      end
+    end
+  end
+end