Add .pick finder

.gitignore

@@ -17,3 +17,4 @@ test/version_tmp
 tmp
 vendor
 .byebug_history
+.idea

README.md

@@ -148,6 +148,7 @@ Country.european.republics.part_of_nato.order(id: :desc)
 ### Supported calculation methods
 
   - count
+  - pick
   - pluck
   - ids
   - minimum

lib/frozen_record/base.rb

@@ -103,7 +103,7 @@ def current_scope=(scope)
       end
 
       delegate :each, :find_each, :where, :first, :first!, :last, :last!,
-               :pluck, :ids, :order, :limit, :offset, :minimum, :maximum, :average, :sum, :count,
+               :pluck, :pick, :ids, :order, :limit, :offset, :minimum, :maximum, :average, :sum, :count,
                to: :current_scope
 
       def file_path

lib/frozen_record/scope.rb

@@ -78,6 +78,12 @@ def pluck(*attributes)
       end
     end
 
+    def pick(*attributes)
+      raise NotImplementedError, '`.pick` without arguments is not supported yet' if attributes.empty?
+
+      limit(1).pluck(*attributes).first
+    end
+
     def ids
       pluck(primary_key)
     end

spec/scope_spec.rb

@@ -352,6 +352,84 @@
 
   end
 
+  describe '.pick' do
+
+    context 'when called with a single argument' do
+
+      it 'returns the value of the first record' do
+        name = Country.pick(:name)
+        expect(name).to be == 'Canada'
+      end
+
+    end
+
+    context 'when called with multiple arguments' do
+
+      it 'returns an array of the values of the first record' do
+        attributes = Country.pick(:id, :name)
+        expect(attributes).to be == [1, 'Canada']
+      end
+
+    end
+
+    context 'when called without arguments' do
+
+      it 'raises a NotImplementedError' do
+        expect { Country.pick }.to raise_error(NotImplementedError)
+      end
+
+    end
+
+    context 'when called on a scope' do
+
+      it 'returns the attribute of the first matching record' do
+        name = Country.where(continent: 'Europe').pick(:name)
+        expect(name).to be == 'France'
+      end
+
+      it 'honors the ordering' do
+        name = Country.order(name: :desc).pick(:name)
+        expect(name).to be == 'France'
+      end
+
+      it 'honors the offset' do
+        name = Country.offset(1).pick(:name)
+        expect(name).to be == 'France'
+      end
+
+      it 'does not alter the receiver scope' do
+        scope = Country.where(nato: true)
+        scope.pick(:name)
+        expect(scope.length).to be == 2
+      end
+
+    end
+
+    context 'when no record matches' do
+
+      it 'returns nil when called with a single argument' do
+        name = Country.where(name: 'not existing').pick(:name)
+        expect(name).to be_nil
+      end
+
+      it 'returns nil when called with multiple arguments' do
+        attributes = Country.where(name: 'not existing').pick(:id, :name)
+        expect(attributes).to be_nil
+      end
+
+    end
+
+    context 'when passed an argument that is not an attribute' do
+
+      it 'returns the result of calling the given method name' do
+        reverse_name = Country.pick(:reverse_name)
+        expect(reverse_name).to be == 'adanaC'
+      end
+
+    end
+
+  end
+
   describe '.ids' do
 
     context 'when called with no arguments' do