Integrate with Active Record

First, register the `ActiveModel::Type::Collection` with
`ActiveRecord::Type`.

Next, add test coverage for writing to and reading from a `TEXT` and
`JSON` column.

Author: seanpdoyle

activemodel/lib/active_model/type/collection.rb

@@ -48,6 +48,8 @@ def serialize(value)
       end
 
       def deserialize(value)
+        return nil if value.nil?
+
         serializer.decode(value).map { |el| @type_object.deserialize(el) }
       end
 
@@ -66,6 +68,8 @@ def changed_in_place?(raw_old_value, new_value)
       end
 
       def valid_value?(value)
+        return true if value.nil?
+
         value.is_a?(Array) && value.all? { |el| @type_object.valid_value?(el) }
       end
 

activerecord/lib/active_record/type.rb

@@ -59,6 +59,7 @@ def current_adapter_name
     BigInteger = ActiveModel::Type::BigInteger
     Binary = ActiveModel::Type::Binary
     Boolean = ActiveModel::Type::Boolean
+    Collection = ActiveModel::Type::Collection
     Decimal = ActiveModel::Type::Decimal
     Float = ActiveModel::Type::Float
     Integer = ActiveModel::Type::Integer
@@ -69,6 +70,7 @@ def current_adapter_name
     register(:big_integer, Type::BigInteger, override: false)
     register(:binary, Type::Binary, override: false)
     register(:boolean, Type::Boolean, override: false)
+    register(:collection, Type::Collection, override: false)
     register(:date, Type::Date, override: false)
     register(:datetime, Type::DateTime, override: false)
     register(:decimal, Type::Decimal, override: false)

activerecord/test/cases/collection_attribute_test.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class CollectionAttributeTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
+
+  class CollectionDataTypeOnText < ActiveRecord::Base
+    attribute :integers, :collection, element_type: :integer
+  end
+
+  class CollectionDataTypeOnJson < ActiveRecord::Base
+    attribute :integers, :collection, element_type: :integer
+  end
+
+  setup do
+    @connection = ActiveRecord::Base.lease_connection
+    @connection.create_table(CollectionDataTypeOnText.table_name, force: true) { |t| t.text :integers }
+    @connection.create_table(CollectionDataTypeOnJson.table_name, force: true) { |t| t.json :integers }
+  end
+
+  teardown do
+    @connection.drop_table CollectionDataTypeOnText.table_name, if_exists: true
+    @connection.drop_table CollectionDataTypeOnJson.table_name, if_exists: true
+    CollectionDataTypeOnText.reset_column_information
+    CollectionDataTypeOnJson.reset_column_information
+  end
+
+  test "writes :collection attribute instance to text column" do
+    integers = ["1", "2", "3"]
+    record = CollectionDataTypeOnText.create!(integers: integers)
+
+    assert_equal integers.map(&:to_i), record.integers
+  end
+
+  test "writes :collection attribute instance to json column" do
+    integers = ["1", "2", "3"]
+    record = CollectionDataTypeOnJson.create!(integers: integers)
+
+    assert_equal integers.map(&:to_i), record.integers
+  end
+
+  test "reads nil :collection attribute instance from text column" do
+    record = CollectionDataTypeOnText.create!(integers: nil)
+
+    assert_empty record.integers
+  end
+
+  test "reads nil :collection attribute instance from json column" do
+    record = CollectionDataTypeOnJson.create!(integers: nil)
+
+    assert_empty record.integers
+  end
+end