Introduce value objects for complex parameter types

README.md

@@ -227,6 +227,41 @@ to run. Since arguments are specified in the user interface via text area
 inputs, it's important to check that they conform to the format your Task
 expects, and to sanitize any inputs if necessary.
 
+The gem provides custom `ActiveModel::Type::Value` objects for complex parameter
+types:
+
+- `IntegerArrayType`: Accepts a comma-delimited string of integers and turns it
+into an array of integers.
+- `StringArrayType`: Accepts an alphanumeric, comma-delimited string and turns
+it into an array of strings.
+
+If you use one of these types for a parameter in your Task, your input will be
+coerced appropriately. **You may still want write validations for your input,
+as type coercion is fairly lax. For example, if you input "xyz" for an
+`IntegerArrayType` parameter, it will be cast to `[0]`.**
+
+```ruby
+# app/tasks/maintenance/update_posts_via_params_task.rb
+module Maintenance
+  class UpdatePostsViaParamsTask < MaintenanceTasks::Task
+    attribute :post_ids, IntegerArrayType.new
+    validates :post_ids, presence: true
+
+    def collection
+      Post.where(ids: post_ids)
+    end
+
+    def count
+      collection.count
+    end
+
+    def process(post)
+      post.update!(content: "New content added on #{Time.now.utc}")
+    end
+  end
+end
+```
+
 ### Considerations when writing Tasks
 
 MaintenanceTasks relies on the queue adapter configured for your application to

app/models/maintenance_tasks/task/integer_array_type.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+module MaintenanceTasks
+  class Task
+    # Type class representing an array of integers. Tasks using the Attributes
+    # API for parameter support can use this class to turn input from the UI
+    # into an array of integers within their Task.
+    class IntegerArrayType < ActiveModel::Type::Value
+      # Casts string from form input field to an array of integers.
+      #
+      # @param input [String] the value to cast to an array of integers.
+      # @return [Array<Integer>] the data cast as an array of integers.
+      def cast(input)
+        return unless input.present?
+        input.split(",").map(&:to_i)
+      end
+    end
+  end
+end

app/models/maintenance_tasks/task/string_array_type.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+module MaintenanceTasks
+  class Task
+    # Type class representing an array of strings. Tasks using the Attributes
+    # API for parameter support can use this class to turn input from the UI
+    # into an array of strings within their Task.
+    class StringArrayType < ActiveModel::Type::Value
+      # Casts string from form input field to an array of strings.
+      #
+      # @param input [String] the value to cast to an array of strings.
+      # @return [Array<Integer>] the data cast as an array of strings.
+      def cast(input)
+        return unless input.present?
+        input.split(",")
+      end
+    end
+  end
+end

test/dummy/app/tasks/maintenance/params_task.rb

@@ -1,18 +1,15 @@
 # frozen_string_literal: true
 module Maintenance
   class ParamsTask < MaintenanceTasks::Task
-    attribute :post_ids, :string
-
-    validates :post_ids,
-      presence: true,
-      format: { with: /\A(\s?\d+(,\s?\d+\s?)*)\z/, allow_blank: true }
+    attribute :post_ids, IntegerArrayType.new
+    validates :post_ids, presence: true
 
     class << self
       attr_accessor :fast_task
     end
 
     def collection
-      Post.where(id: post_ids_array)
+      Post.where(id: post_ids)
     end
 
     def count
@@ -24,11 +21,5 @@ def process(post)
 
       post.update!(content: "New content added on #{Time.now.utc}")
     end
-
-    private
-
-    def post_ids_array
-      post_ids.split(",")
-    end
   end
 end

test/models/maintenance_tasks/run_test.rb

@@ -23,7 +23,7 @@ class RunTest < ActiveSupport::TestCase
     test "invalid if associated Task has parameters and they are invalid" do
       run = Run.new(
         task_name: "Maintenance::ParamsTask",
-        arguments: { post_ids: "xyz" }
+        arguments: { post_ids: "" }
       )
       refute_predicate run, :valid?
     end
@@ -312,7 +312,7 @@ class RunTest < ActiveSupport::TestCase
       run.validate_task_arguments
 
       assert_predicate run, :valid?
-      assert_equal "1,2,3", run.task.post_ids
+      assert_equal [1, 2, 3], run.task.post_ids
     end
 
     private

test/models/maintenance_tasks/task/integer_array_type_test.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+require "test_helper"
+
+module MaintenanceTasks
+  class Task
+    class IntegerArrayTypeTest < ActiveSupport::TestCase
+      test "#cast returns nil if input not present" do
+        assert_nil IntegerArrayType.new.cast("")
+      end
+
+      test "#cast converts string to array of strings" do
+        assert_equal [1, 2, 3], IntegerArrayType.new.cast("1,2,3")
+      end
+
+      test "#cast converts string to array of integers, excluding extra whitespace" do
+        assert_equal [123, 456, 78], IntegerArrayType.new.cast("123 ,456, 78 ")
+      end
+
+      test "#cast handles non-integer input" do
+        assert_equal [0], IntegerArrayType.new.cast("abc")
+      end
+    end
+  end
+end

test/models/maintenance_tasks/task/string_array_type_test.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+require "test_helper"
+
+module MaintenanceTasks
+  class Task
+    class StringArrayTypeTest < ActiveSupport::TestCase
+      test "#cast returns nil if input not present" do
+        assert_nil StringArrayType.new.cast("")
+      end
+
+      test "#cast converts string to array of strings" do
+        assert_equal ["abc", "def"], StringArrayType.new.cast("abc,def")
+      end
+    end
+  end
+end

test/system/maintenance_tasks/runs_test.rb

@@ -49,11 +49,11 @@ class RunsTest < ApplicationSystemTestCase
       visit maintenance_tasks_path
 
       click_on("Maintenance::ParamsTask")
-      fill_in("_task_arguments_post_ids", with: "xyz")
+      fill_in("_task_arguments_post_ids", with: "")
       click_on "Run"
 
-      alert_text = "Validation failed: Arguments are invalid: :post_ids is "\
-        "invalid"
+      alert_text = "Validation failed: Arguments are invalid: "\
+        ":post_ids can't be blank"
       assert_text alert_text
     end