Support conditions in link statements

CHANGELOG.md

@@ -5,6 +5,7 @@
 Breaking changes:
 
 Features:
+- [#2279](https://github.com/rails-api/active_model_serializers/pull/2279) Support condition options in serializer link statements
 
 Fixes:
 

docs/general/serializers.md

@@ -238,6 +238,15 @@ link :other, 'https://example.com/resource'
 link(:posts) { link_author_posts_url(object) }
 ```
 
+Just like attributes, links also support conditions in options
+```ruby
+link(:secret, if: :internal?) { object.secret_link }
+
+def internal?
+  instance_options[:context] == :internal
+end
+```
+
 #### #object
 
 The object being serialized.

lib/active_model/serializer.rb

@@ -21,6 +21,7 @@ class Serializer
     autoload :Adapter
     autoload :Null
     autoload :Attribute
+    autoload :Link
     autoload :Association
     autoload :Reflection
     autoload :SingularReflection
@@ -275,9 +276,14 @@ def self.associate(reflection)
     #   link(:self) { "http://example.com/resource/#{object.id}" }
     # @example
     #   link :resource, "http://example.com/resource"
+    # @example
+    #   link(:callback, if: :internal?), { "http://example.com/callback" }
     #
-    def self.link(name, value = nil, &block)
-      _links[name] = block || value
+    def self.link(name, *args, &block)
+      options = args.extract_options!
+      # For compatibility with the use cae of passing link directly as string argument
+      # without block, we are creating a wrapping block
+      _links[name] = Link.new(name, options, block || ->(_serializer) { args.first })
     end
 
     # Set the JSON API meta attribute of a serializer.

lib/active_model/serializer/link.rb

@@ -0,0 +1,21 @@
+require 'active_model/serializer/field'
+
+module ActiveModel
+  class Serializer
+    # Holds all the data about an serializer link
+    #
+    # @example
+    #   class PostSerializer < ActiveModel::Serializer
+    #     link :callback, if: :internal? do
+    #       object.callback_link
+    #     end
+    #
+    #     def internal?
+    #       instance_options[:internal] == true
+    #     end
+    #   end
+    #
+    class Link < Field
+    end
+  end
+end

lib/active_model_serializers/adapter/json_api.rb

@@ -480,6 +480,10 @@ def relationships_for(serializer, requested_associations, include_slice)
       #   }.reject! {|_,v| v.nil? }
       def links_for(serializer)
         serializer._links.each_with_object({}) do |(name, value), hash|
+          if value.is_a?(ActiveModel::Serializer::Link)
+            next if value.excluded?(serializer)
+            value = value.block
+          end
           result = Link.new(serializer, value).as_json
           hash[name] = result if result
         end

test/adapter/json_api/links_test.rb

@@ -17,7 +17,21 @@ class LinkAuthorSerializer < ActiveModel::Serializer
           link :yet_another do
             "http://example.com/resource/#{object.id}"
           end
+          link :conditional1, if: -> { instance_truth } do
+            "http://example.com/conditional1/#{object.id}"
+          end
+          link :conditional2, if: :instance_falsey do
+            "http://example.com/conditional2/#{object.id}"
+          end
           link(:nil) { nil }
+
+          def instance_truth
+            true
+          end
+
+          def instance_falsey
+            false
+          end
         end
 
         def setup
@@ -85,7 +99,8 @@ def test_resource_links
             :"link-authors" => 'http://example.com/link_authors',
             resource: 'http://example.com/resource',
             posts: 'http://example.com/link_authors/1337/posts',
-            :"yet-another" => 'http://example.com/resource/1337'
+            :"yet-another" => 'http://example.com/resource/1337',
+            conditional1: 'http://example.com/conditional1/1337'
           }
           assert_equal(expected, hash[:data][:links])
         end