change relation to User and fix export

src/stats/admin.py

 from django.contrib import admin
-from import_export.admin import ImportExportModelAdmin
+from import_export.admin import ExportMixin
 
 from . import models
+from . import resources
 
 
 @admin.register(models.Event)
-class EventAdmin(ImportExportModelAdmin):
-    horizontal_filter = ('visitors', )
+class EventAdmin(ExportMixin, admin.ModelAdmin):
+    filter_horizontal = ('visitors', )
+    resource_class = resources.EventResource

src/stats/migrations/0006_auto_20180214_2239.py

+# Generated by Django 2.0.1 on 2018-02-14 21:39
+
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stats', '0005_auto_20180214_2206'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='event',
+            name='visitors',
+            field=models.ManyToManyField(related_name='visitor', to=settings.AUTH_USER_MODEL),
+        ),
+    ]

src/stats/models.py

 from django.db import models
-from account.models import Profile
+from django.contrib.auth.models import User
 from django.utils import timezone
 from django.core.exceptions import ValidationError
 
@@ -7,7 +7,7 @@ from django.core.exceptions import ValidationError
 class Event(models.Model):
     name = models.CharField(max_length=255)
     date = models.DateTimeField(null=False)
-    visitors = models.ManyToManyField(Profile, related_name='visitor')
+    visitors = models.ManyToManyField(User, related_name='visitor')
 
     def clean(self):
         if self.date > timezone.now():

src/stats/resources.py

+from django.contrib.auth.models import User
+from import_export import resources, widgets, fields
+
+from . import models
+
+
+class EventResource(resources.ModelResource):
+    visitors = fields.Field(
+        attribute='visitors',
+        widget=widgets.ManyToManyWidget(model=User, separator=' ,', field='username'),
+    )
+
+    class Meta:
+        model = models.Event
+        fields = (
+            'name',
+            'date',
+            'visitors',
+        )

src/stats/serializers.py

@@ -5,4 +5,4 @@ from . import models
 class EventSerializer(serializers.ModelSerializer):
     class Meta:
         model = models.Event
-        fields = ('date',  'visitors')
+        fields = ('name', 'date', 'visitors')