Rails Join and Includes Not Returning Extra Data

I have two models, Appointment and Teacher. Teacher is a sub-class of User. I want to have a controller return a scope for Appointment but join and includes with Teacher so that I can return all of the data from that table. However, either the data will only be from the Appointment scope or will give me the error Object doesn't support #inspect, primarily when I use the includes or select methods after joins. Did I make a mistake somewhere or is this just not possible?

class Appointment < ApplicationRecord  belongs_to :teacher, class_name: "User"  belongs_to :student, class_name: "User", optional: true  validates :start_datetime, uniqueness: true  scope :all_available_appts, -> { where(status: "Available") }  scope :all_available_appts_for_date, ->(date) { all_available_appts.where(start_datetime: date.to_date.beginning_of_day..date.to_date.end_of_day) }end

class Teacher < User    has_many :appointmentsend

class Student < User    has_many :appointmentsend

 def available_appointments_for_date        student = Student.find_by(id: params[:student_id])        if student            render json: {                appointments: Appointment.all_available_appts_for_date(params[:date]).joins(:teacher).includes(:first_name, :last_name)                 # appointments: Appointment.eager_load(:users).all_available_appts_for_date(params[:date]).select('users.*, appointments.*')            }        else            render json: {                status: 500,                error: "Student or appointments not found"            }        end    end