init project

app/services/private_messages/create_service.rb

@@ -0,0 +1,35 @@
+class PrivateMessages::CreateService < ApplicationService
+  Error = Class.new(StandardError)
+
+  attr_reader :sender, :receiver, :params
+
+  def initialize(sender, receiver, params)
+    @sender   = sender
+    @receiver = receiver
+    @params   = params
+  end
+
+  def call
+    validate!
+
+    same_attr = { sender: sender, receiver: receiver, content: content, send_time: Time.now }
+
+    message = nil
+    ActiveRecord::Base.transaction do
+      message = sender.private_messages.create!(same_attr.merge(target: receiver, status: 1))
+      receiver.private_messages.create!(same_attr.merge(target: sender, status: 0))
+    end
+    message
+  end
+
+  private
+
+  def content
+    @_content ||= params[:content].to_s.strip
+  end
+
+  def validate!
+    raise Error, '内容不能为空' if content.blank?
+    raise Error, '内容太长' if content.size > 500
+  end
+end