Create a context class

main.rb

@@ -22,10 +22,58 @@ before do
 end
 
 get '/words/:id' do
-  $DB_POOL.with do |db_conn|
+  Context.call db_pool: $DB_POOL, user_lang_id: nil do |context|
     word_id = Integer params[:id]
 
-    part_of_speech_name = db_conn.exec_params(
+    json({
+      part_of_speech: context.part_of_speech_name(word_id),
+      examples: context.examples(word_id),
+    })
+  end
+end
+
+class Context
+  private_class_method :new
+
+  def self.call(db_pool:, **kwargs, &block)
+    new(**kwargs).send :call, db_pool: db_pool, &block
+  end
+
+  def initialize(user_lang_id:)
+    self.user_lang_id = user_lang_id
+  end
+
+private
+
+  attr_reader :user_lang_id
+
+  def call(db_pool:)
+    db_pool.with do |db_conn|
+      @db_conn = db_conn
+      result = yield self
+      @db_conn = nil
+      result
+    end
+  end
+
+  def user_lang_id=(user_lang_id)
+    return @user_lang_id = nil if user_lang_id.nil?
+
+    user_lang_id = Integer user_lang_id
+    raise unless user_lang_id.positive?
+
+    @user_lang_id = user_lang_id
+  end
+
+public
+
+  ##
+  # @return [String, nil]
+  #
+  def part_of_speech_name(word_id)
+    word_id = Integer word_id
+
+    column = @db_conn.exec_params(
       (
         <<~SQL
           SELECT parts.english_name
@@ -39,7 +87,17 @@ get '/words/:id' do
       [word_id],
     ).values.first&.first
 
-    examples = db_conn.exec_params(
+    str = String(column).strip.freeze
+    str unless str.empty?
+  end
+
+  ##
+  # @return [Array<Array(String, String)>]
+  #
+  def examples(word_id)
+    word_id = Integer word_id
+
+    result = @db_conn.exec_params(
       (
         <<~SQL
           SELECT
@@ -75,9 +133,6 @@ get '/words/:id' do
       [word_id],
     ).map { |row| row['values'] }
 
-    json({
-      part_of_speech: part_of_speech_name,
-      examples: examples,
-    })
+    result.map { |pair| pair.map(&:freeze).freeze }.freeze
   end
 end