old_contents: 
  from rest_framework import serializers
  from roledb.models import User
  
  
  class UserSerializer(serializers.ModelSerializer):
    roles = serializers.SerializerMethodField('role_data')
    attributes = serializers.SerializerMethodField('attribute_data')
  
    class Meta:
      model = User
      fields = ('username', 'roles', 'attributes')
  
    def role_data(self, obj):
      data = []
      for a in obj.attendances.all():
        d = {}
        d['school'] = a.school.school_id
        d['group'] = a.group
        d['role'] = a.role.name
        data.append(d)
      return data
  
    def attribute_data(self, obj):
      data = []
      for a in obj.attributes.all():
        d = {}
        d['name'] = a.attribute.name
        d['value'] = a.value
        data.append(d)
      return data
  
  
  
new_contents: 
  from rest_framework import serializers
  from roledb.models import User
  
  
  class UserSerializer(serializers.ModelSerializer):
    roles = serializers.SerializerMethodField('role_data')
    attributes = serializers.SerializerMethodField('attribute_data')
  
    class Meta:
      model = User
      fields = ('username','first_name','last_name','roles','attributes')
  
    def role_data(self, obj):
      data = []
      for a in obj.attendances.all():
        d = {}
        d['school'] = a.school.school_id
        d['group'] = a.group
        d['role'] = a.role.name
        data.append(d)
      return data
  
    def attribute_data(self, obj):
      data = []
      for a in obj.attributes.all():
        d = {}
        d['name'] = a.attribute.name
        d['value'] = a.value
        data.append(d)
      return data
  
  
  
subject: Send first_name and last_name in JSON.