Relation.where with no args can be chained with not, like, and not_like

examples:

  Model.where.not field: nil
  #=> "SELECT * FROM models WHERE field IS NOT NULL

  Model.where.like name: 'Jeremy%'
  #=> "SELECT * FROM models WHERE name LIKE 'Jeremy%'

this feature was originally suggested by Jeremy Kemper https://github.com/rails/rails/pull/5950#issuecomment-5591330

Closes #5950

4 files changed, 184 insertions, 8 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 66359fb80f..a8c5ffeaed 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,14 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Allow `Relation#where` with no arguments to be chained with new query methods
+    `not`, `like`, and `not_like`.
+
+    Example:
+
+        Developer.where.not(name: 'Aaron').where.like(name: 'Takoyaki%')
+
+    *Akira Matsuda*
+
 *   Fix dirty attribute checks for TimeZoneConversion with nil and blank
     datetime attributes. Setting a nil datetime to a blank string should not
     result in a change being flagged. Fix #8310
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index b3712b4ad6..5e79c5489f 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -4,6 +4,68 @@ module ActiveRecord
   module QueryMethods
     extend ActiveSupport::Concern
 
+    # WhereChain objects act as placeholder for queries in which #where does not have any parameter.
+    # In this case, #where must be chained with either #not, #like, or #not_like to return a new relation.
+    class WhereChain
+      def initialize(scope)
+        @scope = scope
+      end
+
+      # Returns a new relation expressing WHERE + NOT condition
+      # according to the conditions in the arguments.
+      #
+      #    User.where.not(name: "Jon")
+      #    # SELECT * FROM users WHERE name <> 'Jon'
+      #
+      #    User.where.not(name: nil)
+      #    # SELECT * FROM users WHERE name IS NOT NULL
+      #
+      #    User.where.not(name: %(Ko1 Nobu))
+      #    # SELECT * FROM users WHERE name NOT IN ('Ko1', 'Nobu')
+      def not(opts, *rest)
+        where_value = @scope.send(:build_where, opts, rest).map do |rel|
+          case rel
+          when Arel::Nodes::Equality
+            Arel::Nodes::NotEqual.new(rel.left, rel.right)
+          when Arel::Nodes::In
+            Arel::Nodes::NotIn.new(rel.left, rel.right)
+          when String
+            Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(rel))
+          else
+            Arel::Nodes::Not.new(rel)
+          end
+        end
+        @scope.where_values += where_value
+        @scope
+      end
+
+      # Returns a new relation expressing WHERE + LIKE condition
+      # according to the conditions in the arguments.
+      #
+      #    Book.where.like(title: "Rails%")
+      #    # SELECT * FROM books WHERE title LIKE 'Rails%'
+      def like(opts, *rest)
+        where_value = @scope.send(:build_where, opts, rest).map do |rel|
+          Arel::Nodes::Matches.new(rel.left, rel.right)
+        end
+        @scope.where_values += where_value
+        @scope
+      end
+
+      # Returns a new relation expressing WHERE + NOT LIKE condition
+      # according to the conditions in the arguments.
+      #
+      #    Conference.where.not_like(name: "%Kaigi")
+      #    # SELECT * FROM conferences WHERE name NOT LIKE '%Kaigi'
+      def not_like(opts, *rest)
+        where_value = @scope.send(:build_where,  opts, rest).map do |rel|
+          Arel::Nodes::DoesNotMatch.new(rel.left, rel.right)
+        end
+        @scope.where_values += where_value
+        @scope
+      end
+    end
+
     Relation::MULTI_VALUE_METHODS.each do |name|
       class_eval <<-CODE, __FILE__, __LINE__ + 1
         def #{name}_values                   # def select_values
@@ -379,20 +441,47 @@ module ActiveRecord
     #    User.joins(:posts).where({ "posts.published" => true })
     #    User.joins(:posts).where({ posts: { published: true } })
     #
+    # === no argument or nil
+    #
+    # If no argument or nil is passed, #where returns a new instance of WhereChain which, when
+    # chained with either #not, #like, or #not_like, returns a new relation.
+    #
+    #    User.where.not(name: "Jon")
+    #    # SELECT * FROM users WHERE name <> 'Jon'
+    #
+    #    Book.where.like(title: "Rails%")
+    #    # SELECT * FROM books WHERE title LIKE 'Rails%'
+    #
+    #    Conference.where.not_like(name: "%Kaigi")
+    #    # SELECT * FROM conferences WHERE name NOT LIKE '%Kaigi'
+    #
+    # See WhereChain for more details on #not, #like, and #not_like.
+    #
     # === empty condition
     #
-    # If the condition returns true for blank?, then where is a no-op and returns the current relation.
-    def where(opts, *rest)
-      opts.blank? ? self : spawn.where!(opts, *rest)
+    # If the condition is any other blank-ish object than nil, then where is a # no-op and returns
+    # the current relation.
+    def where(opts = nil, *rest)
+      if opts.nil?
+        WhereChain.new(spawn)
+      elsif opts.blank?
+        self
+      else
+        spawn.where!(opts, *rest)
+      end
     end
 
     # #where! is identical to #where, except that instead of returning a new relation, it adds
     # the condition to the existing relation.
-    def where!(opts, *rest)
-      references!(PredicateBuilder.references(opts)) if Hash === opts
+    def where!(opts = nil, *rest)
+      if opts.nil?
+        WhereChain.new(self)
+      else
+        references!(PredicateBuilder.references(opts)) if Hash === opts
 
-      self.where_values += build_where(opts, rest)
-      self
+        self.where_values += build_where(opts, rest)
+        self
+      end
     end
 
     # Allows to specify a HAVING clause. Note that you can't use HAVING
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index e5022d49f1..664f636176 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -271,7 +271,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_with_blank_conditions
-    [[], {}, nil, ""].each do |blank|
+    [[], {}, ""].each do |blank|
       assert_equal 2, Firm.all.merge!(:order => "id").first.clients.where(blank).to_a.size
     end
   end
diff --git a/activerecord/test/cases/relation/where_chain_test.rb b/activerecord/test/cases/relation/where_chain_test.rb
new file mode 100644
index 0000000000..10b19da3fd
--- /dev/null
+++ b/activerecord/test/cases/relation/where_chain_test.rb
@@ -0,0 +1,78 @@
+require 'cases/helper'
+require 'models/post'
+require 'models/comment'
+
+module ActiveRecord
+  class WhereChainTest < ActiveRecord::TestCase
+    fixtures :posts
+
+    def test_not_eq
+      expected = Arel::Nodes::NotEqual.new(Post.arel_table[:title], 'hello')
+      relation = Post.where.not(title: 'hello')
+      assert_equal([expected], relation.where_values)
+    end
+
+    def test_not_null
+      expected = Arel::Nodes::NotEqual.new(Post.arel_table[:title], nil)
+      relation = Post.where.not(title: nil)
+      assert_equal([expected], relation.where_values)
+    end
+
+    def test_not_in
+      expected = Arel::Nodes::NotEqual.new(Post.arel_table[:title], %w[hello goodbye])
+      relation = Post.where.not(title: %w[hello goodbye])
+      assert_equal([expected], relation.where_values)
+    end
+
+    def test_association_not_eq
+      expected = Arel::Nodes::NotEqual.new(Comment.arel_table[:title], 'hello')
+      relation = Post.joins(:comments).where.not(comments: {title: 'hello'})
+      assert_equal(expected.to_sql, relation.where_values.first.to_sql)
+    end
+
+    def test_not_eq_with_preceding_where
+      relation = Post.where(title: 'hello').where.not(title: 'world')
+
+      expected = Arel::Nodes::Equality.new(Post.arel_table[:title], 'hello')
+      assert_equal(expected, relation.where_values.first)
+
+      expected = Arel::Nodes::NotEqual.new(Post.arel_table[:title], 'world')
+      assert_equal(expected, relation.where_values.last)
+    end
+
+    def test_not_eq_with_succeeding_where
+      relation = Post.where.not(title: 'hello').where(title: 'world')
+
+      expected = Arel::Nodes::NotEqual.new(Post.arel_table[:title], 'hello')
+      assert_equal(expected, relation.where_values.first)
+
+      expected = Arel::Nodes::Equality.new(Post.arel_table[:title], 'world')
+      assert_equal(expected, relation.where_values.last)
+    end
+
+    def test_like
+      expected = Arel::Nodes::Matches.new(Post.arel_table[:title], 'a%')
+      relation = Post.where.like(title: 'a%')
+      assert_equal([expected], relation.where_values)
+    end
+
+    def test_not_like
+      expected = Arel::Nodes::DoesNotMatch.new(Post.arel_table[:title], 'a%')
+      relation = Post.where.not_like(title: 'a%')
+      assert_equal([expected], relation.where_values)
+    end
+
+    def test_chaining_multiple
+      relation = Post.where.like(title: 'ruby on %').where.not(title: 'ruby on rails').where.not_like(title: '% ales')
+
+      expected = Arel::Nodes::Matches.new(Post.arel_table[:title], 'ruby on %')
+      assert_equal(expected, relation.where_values[0])
+
+      expected = Arel::Nodes::NotEqual.new(Post.arel_table[:title], 'ruby on rails')
+      assert_equal(expected, relation.where_values[1])
+
+      expected = Arel::Nodes::DoesNotMatch.new(Post.arel_table[:title], '% ales')
+      assert_equal(expected, relation.where_values[2])
+    end
+  end
+end