Implemented chosen tags by adding priority field: chosen tags should have non-null priority field, other tags should have null priority field.

apps/tag/migrations/0003_tag_priority.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.4 on 2019-10-18 15:25
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('tag', '0002_auto_20191009_1408'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='tag',
+            name='priority',
+            field=models.IntegerField(default=None, null=True, unique=True),
+        ),
+    ]

apps/tag/models.py

@@ -14,6 +14,8 @@ class Tag(TranslatedFieldsMixin, models.Model):
     category = models.ForeignKey('TagCategory', on_delete=models.PROTECT,
                                  null=True, related_name='tags',
                                  verbose_name=_('Category'))
+    # chosen tags should have non-null priority,other tags priority should be null
+    priority = models.IntegerField(unique=True, null=True, default=None)
 
     class Meta:
         """Meta class."""