add balance entity

app/controllers/admin/balances_controller.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+module Admin
+  class BalancesController < Admin::ApplicationController
+  end
+end

app/controllers/admin/currencies_controller.rb

@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 module Admin
   class CurrenciesController < Admin::ApplicationController
+    def valid_action?(name, resource = resource_class)
+      ["new", "edit", "destroy"].exclude?(name.to_s) && super
+    end
   end
 end

app/dashboards/balance_dashboard.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+require "administrate/base_dashboard"
+
+class BalanceDashboard < Administrate::BaseDashboard
+  # ATTRIBUTE_TYPES
+  # a hash that describes the type of each of the model's fields.
+  #
+  # Each different type represents an Administrate::Field object,
+  # which determines how the attribute is displayed
+  # on pages throughout the dashboard.
+  ATTRIBUTE_TYPES = {
+    user: Field::BelongsTo,
+    currency: Field::BelongsTo,
+    id: Field::Number,
+    amount: Field::String.with_options(searchable: false),
+    created_at: Field::DateTime,
+    updated_at: Field::DateTime,
+  }.freeze
+
+  # COLLECTION_ATTRIBUTES
+  # an array of attributes that will be displayed on the model's index page.
+  #
+  # By default, it's limited to four items to reduce clutter on index pages.
+  # Feel free to add, remove, or rearrange items.
+  COLLECTION_ATTRIBUTES = [:user, :currency, :id, :amount].freeze
+
+  # SHOW_PAGE_ATTRIBUTES
+  # an array of attributes that will be displayed on the model's show page.
+  SHOW_PAGE_ATTRIBUTES = [:user, :currency, :id, :amount, :created_at, :updated_at].freeze
+
+  # FORM_ATTRIBUTES
+  # an array of attributes that will be displayed
+  # on the model's form (`new` and `edit`) pages.
+  FORM_ATTRIBUTES = [:user, :currency, :amount].freeze
+
+  # COLLECTION_FILTERS
+  # a hash that defines filters that can be used while searching via the search
+  # field of the dashboard.
+  #
+  # For example to add an option to search for open resources by typing "open:"
+  # in the search field:
+  #
+  #   COLLECTION_FILTERS = {
+  #     open: ->(resources) { resources.where(open: true) }
+  #   }.freeze
+  COLLECTION_FILTERS = {}.freeze
+
+  # Overwrite this method to customize how balances are displayed
+  # across all pages of the admin dashboard.
+  #
+  # def display_resource(balance)
+  #   "Balance ##{balance.id}"
+  # end
+end

app/dashboards/currency_dashboard.rb

@@ -46,7 +46,7 @@ class CurrencyDashboard < Administrate::BaseDashboard
   # Overwrite this method to customize how currencies are displayed
   # across all pages of the admin dashboard.
   #
-  # def display_resource(currency)
-  #   "Currency ##{currency.id}"
-  # end
+  def display_resource(currency)
+    currency.name
+  end
 end

app/models/balance.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: balances
+#
+#  id          :bigint           not null, primary key
+#  amount      :decimal(20, 10)  default(0.0), not null
+#  created_at  :datetime         not null
+#  updated_at  :datetime         not null
+#  currency_id :bigint           not null
+#  user_id     :bigint           not null
+#
+# Indexes
+#
+#  index_balances_on_currency_id  (currency_id)
+#  index_balances_on_user_id      (user_id)
+#
+# Foreign Keys
+#
+#  fk_rails_...  (currency_id => currencies.id)
+#  fk_rails_...  (user_id => users.id)
+#
+class Balance < ApplicationRecord
+  belongs_to :user
+  belongs_to :currency
+
+  validates :amount, presence: true
+end

app/models/user.rb

@@ -25,6 +25,7 @@ class User < ApplicationRecord
     :recoverable, :rememberable, :validatable
 
   has_many :documents, class_name: "UserDocument", dependent: :destroy
+  has_many :balances, dependent: :restrict_with_error
 
   validates :first_name, :last_name, :email, presence: true
   validates :email, uniqueness: true