task.rb

class Task
  attr_reader :id, :title
  attr_accessor :done

  def initialize(args = {})
    @id = args[:id]
    @title = args[:title]
    @description = args[:description]
    @done = args[:done] || false
  end

  def save
    if @id
      DB.execute("UPDATE tasks SET title = ?, description = ?, done = ? WHERE id = ?", @title, @description, @done ? 1 : 0, @id)
    else
      query = <<SQL
    INSERT INTO tasks (title, description, done) VALUES (?, ?, ?)
SQL
      DB.execute(query, @title, @description, @done ? 1 : 0)
      @id = DB.last_insert_row_id
    end
  end
  #
  def self.find(id)
    DB.results_as_hash = true
    rows = DB.execute("SELECT * FROM tasks WHERE id = ?", id)
    row = rows.first
    Task.build_task(row)
  end
  #
  def self.all
    DB.results_as_hash = true
    rows = DB.execute("SELECT * FROM tasks")
    return rows.map { |row| Task.build_task(row)  }
  end

  def destroy
    DB.execute("DELETE FROM tasks WHERE id = ?", @id)
  end
  #
  private

  def self.build_task(row)
    Task.new(id: row['id'],
             title: row['title'],
             description: row['description'],
             done: (row['done'] == 1)
            )
  end
end

test.rb

require "sqlite3"
require "pry-byebug"

db_file_path = File.join(File.dirname(__FILE__), "tasks.db")
DB = SQLite3::Database.new(db_file_path)
# above lines must be kept
#
require_relative "task.rb"

# task = Task.new(title: "Faire la vaisselle", description: "Surtout bien frotter")
# task.save
# p task

# task = Task.find(10)
# p task
# task.destroy
#

tasks = Task.all
tasks.each do |task|
  puts "#{task.id} - #{task.title}"
end

task = Task.find(11)
task.done = true
task.save
p task