6 files changed, 114 insertions, 0 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 1d5b8841e2..26f6093bc2 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,15 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Added `#find_by` and `#find_by!` to mirror the functionality
+    provided by dynamic finders in a way that allows dynamic input more
+    easily:
+
+        Post.find_by name: 'Spartacus', rating: 4
+        Post.find_by "published_at < ?", 2.weeks.ago
+        Post.find_by! name: 'Spartacus'
+
+    *Jon Leighton*
+
 *   Added ActiveRecord::Base#slice to return a hash of the given methods with
     their names as keys and returned values as values.
 
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 0e6fecbc4b..95565b503a 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -5,6 +5,7 @@ module ActiveRecord
   module Querying
     delegate :find, :first, :first!, :last, :last!, :all, :exists?, :any?, :many?, :to => :scoped
     delegate :first_or_create, :first_or_create!, :first_or_initialize, :to => :scoped
+    delegate :find_by, :find_by!, :to => :scoped
     delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, :to => :scoped
     delegate :find_each, :find_in_batches, :to => :scoped
     delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins,
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 2c74f4011d..74f8e30404 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -109,6 +109,25 @@ module ActiveRecord
       end
     end
 
+    # Finds the first record matching the specified conditions. There
+    # is no implied ording so if order matters, you should specify it
+    # yourself.
+    #
+    # If no record is found, returns <tt>nil</tt>.
+    #
+    #   Post.find_by name: 'Spartacus', rating: 4
+    #   Post.find_by "published_at < ?", 2.weeks.ago
+    #
+    def find_by(*args)
+      where(*args).first
+    end
+
+    # Like <tt>find_by</tt>, except that if no record is found, raises
+    # an <tt>ActiveRecord::RecordNotFound</tt> error.
+    def find_by!(*args)
+      where(*args).first!
+    end
+
     # A convenience wrapper for <tt>find(:first, *args)</tt>. You can pass in all the
     # same arguments to this method as you can to <tt>find(:first)</tt>.
     def first(*args)
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index f0fbca190c..5fb49d540f 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -2069,4 +2069,18 @@ class BasicsTest < ActiveRecord::TestCase
     assert_nil hash[:firm_name]
     assert_nil hash['firm_name']
   end
+
+  ["find_by", "find_by!"].each do |meth|
+    test "#{meth} delegates to scoped" do
+      record = stub
+
+      scope = mock
+      scope.expects(meth).with(:foo, :bar).returns(record)
+
+      klass = Class.new(ActiveRecord::Base)
+      klass.stubs(:scoped => scope)
+
+      assert_equal record, klass.public_send(meth, :foo, :bar)
+    end
+  end
 end
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 3edc237c44..25eb7c1672 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1256,4 +1256,38 @@ class RelationTest < ActiveRecord::TestCase
 
     assert topics.loaded?
   end
+
+  test "find_by with hash conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.order(:id).find_by(author_id: 2)
+  end
+
+  test "find_by with non-hash conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.order(:id).find_by("author_id = 2")
+  end
+
+  test "find_by with multi-arg conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.order(:id).find_by('author_id = ?', 2)
+  end
+
+  test "find_by returns nil if the record is missing" do
+    assert_equal nil, Post.scoped.find_by("1 = 0")
+  end
+
+  test "find_by! with hash conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.order(:id).find_by!(author_id: 2)
+  end
+
+  test "find_by! with non-hash conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.order(:id).find_by!("author_id = 2")
+  end
+
+  test "find_by! with multi-arg conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.order(:id).find_by!('author_id = ?', 2)
+  end
+
+  test "find_by! raises RecordNotFound if the record is missing" do
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Post.scoped.find_by!("1 = 0")
+    end
+  end
 end
diff --git a/guides/source/active_record_querying.textile b/guides/source/active_record_querying.textile
index 8e23a577e2..8471d67def 100644
--- a/guides/source/active_record_querying.textile
+++ b/guides/source/active_record_querying.textile
@@ -133,6 +133,24 @@ SELECT * FROM clients ORDER BY clients.id DESC LIMIT 1
 
 <tt>Model.last</tt> returns +nil+ if no matching record is found. No exception will be raised.
 
+h5. +find_by+
+
+<tt>Model.find_by</tt> finds the first record matching some conditions. For example:
+
+<ruby>
+Client.find_by first_name: 'Lifo'
+# => #<Client id: 1, first_name: "Lifo">
+
+Client.find_by first_name: 'Jon'
+# => nil
+</ruby>
+
+It is equivalent to writing:
+
+<ruby>
+Client.where(first_name: 'Lifo').first
+</ruby>
+
 h5(#first_1). +first!+
 
 <tt>Model.first!</tt> finds the first record. For example:
@@ -167,6 +185,24 @@ SELECT * FROM clients ORDER BY clients.id DESC LIMIT 1
 
 <tt>Model.last!</tt> raises +RecordNotFound+ if no matching record is found.
 
+h5(#find_by_1). +find_by!+
+
+<tt>Model.find_by!</tt> finds the first record matching some conditions. It raises +RecordNotFound+ if no matching record is found. For example:
+
+<ruby>
+Client.find_by! first_name: 'Lifo'
+# => #<Client id: 1, first_name: "Lifo">
+
+Client.find_by! first_name: 'Jon'
+# => RecordNotFound
+</ruby>
+
+It is equivalent to writing:
+
+<ruby>
+Client.where(first_name: 'Lifo').first!
+</ruby>
+
 h4. Retrieving Multiple Objects
 
 h5. Using Multiple Primary Keys