Refactor class methods of MaskedDatum

- Avoid using class variables https://github.com/cookpad/styleguide/blob/master/ruby.en.md#variables
    - But class_attribute with the default value which is calculated using an instance method is a bit difficult
- Remove cache and query directly, in order to remove both class variables and class_attributes
    - The calculation cost will be roughly the same

app/controllers/table_memos_controller.rb

@@ -12,7 +12,11 @@ def show(database_name, schema_name, name)
       take!
     @raw_dataset = @table_memo.raw_dataset
     if @raw_dataset
-      @raw_dataset_columns = @raw_dataset.columns.order(:position)
+      @masked_columns = MaskedDatum.masked_columns(database_name, name)
+      @raw_dataset_columns = @raw_dataset.columns.order(:position).map { |column| {
+        data: column,
+        masked: @masked_columns.include?(::MaskedDatum::ANY_NAME) || @masked_columns.include?(column.name),
+      }}
       @raw_dataset_rows = @raw_dataset.rows.pluck(:row)
     end
     @view_meta_data = @table_memo.view_meta_data

app/models/masked_datum.rb

@@ -1,38 +1,32 @@
 class MaskedDatum < ApplicationRecord
-  validates :database_name, :table_name, :column_name, presence: true
-
-  after_save :update_data!
+  ANY_NAME = "*".freeze
 
-  def self.data
-    @@data ||= update_data!
-  end
+  validates :database_name, :table_name, :column_name, presence: true
 
-  def self.update_data!
-    @@data = all.map(&:pack)
-  end
+  scope :masking_database, ->(database_name) {
+    where(database_name: database_name, table_name: ANY_NAME, column_name: ANY_NAME)
+  }
+  scope :masking_table, ->(database_name, table_name) {
+    masking_database(database_name)
+      .or(where(database_name: database_name, table_name: table_name, column_name: ANY_NAME))
+      .or(where(database_name: ANY_NAME, table_name: table_name, column_name: ANY_NAME))
+  }
 
   def self.masked_database?(database_name)
-    data.include?("#{database_name}/*/*")
+    self.masking_database(database_name).exists?
   end
 
   def self.masked_table?(database_name, table_name)
-    return true if masked_database?(database_name)
-    data.include?("#{database_name}/#{table_name}/*")
+    self.masking_table(database_name, table_name).exists?
   end
 
-  def self.masked_column?(database_name, table_name, column_name)
-    return true if masked_database?(database_name)
-    return true if masked_table?(database_name, table_name)
-    data.include?("#{database_name}/#{table_name}/#{column_name}") || data.include?("#{database_name}/*/#{column_name}") || data.include?("*/*/#{column_name}")
+  def self.masked_columns(database_name, table_name)
+    return [ANY_NAME] if self.masked_table?(database_name, table_name)
+
+    Set.new(self.where(database_name: database_name, table_name: table_name).pluck(:column_name))
   end
 
   def pack
     "#{database_name}/#{table_name}/#{column_name}"
   end
-
-  private
-
-  def update_data!
-    self.class.update_data!
-  end
 end

app/views/table_memos/_raw_dataset.html.haml

@@ -6,7 +6,7 @@
       %table.table.table-hover.table-bordered.table-striped.text-sm{ role: "grid" }
         %tr
           - @raw_dataset_columns.each do |column|
-            %th #{column.name} (#{column.sql_type})
+            %th #{column.fetch(:data).name} (#{column.fetch(:data).sql_type})
         - if @table_memo.masked?
           %tr
             %td.text-center{ colspan: @raw_dataset_columns.size }
@@ -18,7 +18,7 @@
             %tr
               - Array.wrap(row).zip(@raw_dataset_columns).each_with_index do |(value, column), i|
                 %td
-                  - if MaskedDatum.masked_column?(database_name, table_name, column.name)
+                  - if column.fetch(:masked)
                     = t("masked_text")
                   - else
                     = value