Enables infinite precision on Money attributes based on column type

lib/money-rails/active_record/monetizable.rb

@@ -55,6 +55,9 @@ def monetize(*fields)
                                    "Use :as option to explicitly specify the name or change the amount column postfix in the initializer."
             end
 
+            # Assigns infinite_precision based on the field's column type, if available
+            options[:infinite_precision] = self.columns_hash[subunit_name].try(:type) == :decimal
+
             # Optional accessor to be run on an instance to detect currency
             instance_currency_name = options[:with_model_currency] ||
               options[:model_currency] ||
@@ -194,14 +197,14 @@ def read_monetized(name, subunit_name, options = {}, *args)
           if memoized.currency == attr_currency
             result = memoized
           else
-            memoized_amount = memoized.amount.to_money(attr_currency)
+            memoized_amount = memoized.amount.to_money(attr_currency, options.slice(:infinite_precision))
             write_attribute subunit_name, memoized_amount.cents
             # Cache the value (it may be nil)
             result = instance_variable_set("@#{name}", memoized_amount)
           end
         elsif amount.present?
           # If amount is NOT nil (or empty string) load the amount in a Money
-          amount = Money.new(amount, attr_currency)
+          amount = Money.new(amount, attr_currency, options.slice(:infinite_precision))
 
           # Cache the value (it may be nil)
           result = instance_variable_set("@#{name}", amount)
@@ -230,7 +233,7 @@ def write_monetized(name, subunit_name, value, validation_enabled, instance_curr
             money = value
           else
             begin
-              money = value.to_money(public_send("currency_for_#{name}"))
+              money = value.to_money(public_send("currency_for_#{name}"), options.slice(:infinite_precision))
             rescue NoMethodError
               return nil
             rescue Money::Currency::UnknownCurrency, Monetize::ParseError => e

spec/active_record/monetizable_spec.rb

@@ -12,7 +12,9 @@ class Sub < Product; end
                      sale_price_amount: 1200, delivery_fee_cents: 100,
                      restock_fee_cents: 2000,
                      reduced_price_cents: 1500, reduced_price_currency: :lvl,
-                     lambda_price_cents: 4000)
+                     lambda_price_cents: 4000,
+                     unit_cost_cents: 1234.8765
+                    )
     end
 
     describe ".monetize" do
@@ -141,6 +143,16 @@ class SubProduct < Product
         expect(product.discount_value).to eq(Money.new(150, "USD"))
       end
 
+      it "assigns instance precision based on the column type of the attribute" do
+        expect(product.unit_cost.infinite_precision?).to eq(true)
+        expect(product.unit_cost).to eq(Money.new(1234.8765, "USD", infinite_precision: true))
+        expect(product.unit_cost.to_s).to eq("12.348765")
+
+        expect(product.price.infinite_precision?).to eq(false)
+        expect(product.price).to eq(Money.new(3000, "USD", infinite_precision: false))
+        expect(product.price.to_s).to eq("30.00")
+      end
+
       it "uses numericality validation" do
         product.price_cents = "foo"
         expect(product.save).to be_falsey

spec/dummy/app/models/product.rb

@@ -56,4 +56,7 @@ class Product < ActiveRecord::Base
 
   # Using postfix to determine currency column (reduced_price_currency)
   monetize :reduced_price_cents, allow_nil: true
+
+  # Enable infinite_precision on this attribute
+  monetize :unit_cost_cents, allow_nil: true
 end

spec/dummy/db/migrate/20190814150759_add_precision_unit_cost_to_products.rb

@@ -0,0 +1,5 @@
+class AddPrecisionUnitCostToProducts < (Rails::VERSION::MAJOR >= 5 ? ActiveRecord::Migration[4.2] : ActiveRecord::Migration)
+  def change
+    add_column :products, :unit_cost_cents, :decimal
+  end
+end

spec/dummy/db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20151026220420) do
+ActiveRecord::Schema.define(version: 20190814150759) do
 
   create_table "dummy_products", force: :cascade do |t|
     t.string   "currency"
@@ -39,6 +39,7 @@
     t.integer  "special_price_cents"
     t.integer  "lambda_price_cents"
     t.string   "skip_validation_price_cents"
+    t.decimal  "unit_cost_cents"
   end
 
   create_table "services", force: :cascade do |t|