feature(backend): Add model and migration

backend/stats_app/migrations/0002_auto_20200601_1418.py

+# Generated by Django 2.1.7 on 2020-06-01 12:18
+
+import django.core.validators
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("backend_app", "0005_lastvisiteduniversity"),
+        ("stats_app", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="DailyExchangeContributionsInfo",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("date", models.DateTimeField()),
+                ("major", models.CharField(blank=True, max_length=20)),
+                ("minor", models.CharField(blank=True, max_length=47)),
+                ("exchange_semester", models.CharField(max_length=5)),
+                (
+                    "nb_contributions",
+                    models.IntegerField(
+                        validators=[django.core.validators.MinValueValidator(0)]
+                    ),
+                ),
+                (
+                    "university",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        to="backend_app.University",
+                    ),
+                ),
+            ],
+        ),
+        migrations.AlterUniqueTogether(
+            name="dailyexchangecontributionsinfo",
+            unique_together={
+                ("date", "university", "major", "minor", "exchange_semester")
+            },
+        ),
+    ]

backend/stats_app/models.py

 from django.db import models
 from django.core.validators import MinValueValidator
+from backend_app.models.university import University
 
 
 class DailyConnections(models.Model):
     date = models.DateTimeField(unique=True, null=False)
     nb_connections = models.IntegerField(validators=[MinValueValidator(0)], null=False)
+
+
+class DailyExchangeContributionsInfo(models.Model):
+    date = models.DateTimeField(null=False)
+    university = models.ForeignKey(University, null=False, on_delete=models.CASCADE)
+    major = models.CharField(max_length=20, null=False, blank=True)
+    minor = models.CharField(max_length=47, null=False, blank=True)
+    exchange_semester = models.CharField(max_length=5, null=False)
+    nb_contributions = models.IntegerField(
+        validators=[MinValueValidator(0)], null=False
+    )
+
+    class Meta:
+        unique_together = ("date", "university", "major", "minor", "exchange_semester")