title: django-import-export :ForeignKey with many fields
body: <p>I need just export data from my admin. My code now looks like:</p>
  
  <pre><code>models.py
  
   from django.db import models
  from services.models import Services,PromoCodes,CauseOfReservedPromocodes
  # Create your models here.
  
  class User(models.Model):
      name=models.CharField(max_length=200)
      surname=models.CharField(max_length=200)
      email=models.EmailField()
      password=models.CharField(max_length=200)
     telephone=models.PositiveIntegerField(max_length=12,blank=True,null=True)
      userRequest=models.ForeignKey('UsersRequests', blank=True, null=True, on_delete=models.CASCADE)
  
      def __str__(self):
          return self.name + " " + self.surname
  
  
  class UsersRequests(models.Model):
      date = models.DateField()
      requestChannel = models.CharField(max_length=30)
      problem = models.CharField(max_length=200)
      solution = models.CharField(max_length=200)
  
      def __unicode__(self):
          return str(self.date) + " " + str(self.requestChannel) + " " + str(self.problem) + " " + str(self.solution)
  </code></pre>
  
  <p>And my admin.py is:</p>
  
  <pre><code>from django.contrib import admin
  from .models import User,UsersRequests
  from import_export import resources, widgets, fields
  from import_export.admin import ImportExportModelAdmin,ExportMixin
  
  class UsersResource(resources.ModelResource):
   class Meta:
          model = User
          fields = ('id', 'name', 'email', 'telephone', 'userRequest')
  
  class UserAdmin(ImportExportModelAdmin):
      resource_class = UsersResource
  
  @admin.register(User)
  class UserAdmin(ImportExportModelAdmin):
      search_fields = ('name', 'surname', 'email', 'telephone')
  </code></pre>
  
  <p>I try everything to get userRequest work, but it send just integer - id for userRequest. How to get full data from class UsersRequests(models.Model)?</p>