Add django model and migration for grant reimbursement

This change introduces a new GrantReimbursement model and related migration
to support flexible grant reimbursement categories. The model links grants
to their reimbursement categories and stores the granted amount for each.

Key changes:
- Add `GrantReimbursement` model as through table for M2M relationship
- Add `reimbursement_categories` M2M field to `Grant` model
- Create migration for the new model and relationship
- Add factory for testing

This change enables more granular control over grant reimbursements by
allowing different categories (e.g., travel, accommodation) with specific
amounts for each category.

Author: estyxx

backend/grants/admin.py

@@ -30,7 +30,12 @@
 )
 from schedule.models import ScheduleItem
 from submissions.models import Submission
-from .models import Grant, GrantConfirmPendingStatusProxy, GrantReimbursementCategory
+from .models import (
+    Grant,
+    GrantConfirmPendingStatusProxy,
+    GrantReimbursementCategory,
+    GrantReimbursement,
+)
 from django.db.models import Exists, OuterRef, F
 from pretix import user_has_admission_ticket
 
@@ -399,6 +404,18 @@ class GrantReimbursementCategoryAdmin(ConferencePermissionMixin, admin.ModelAdmi
     list_filter = ("conference", "category", "included_by_default")
 
 
+@admin.register(GrantReimbursement)
+class GrantReimbursementAdmin(ConferencePermissionMixin, admin.ModelAdmin):
+    list_display = (
+        "grant",
+        "category",
+        "granted_amount",
+    )
+    list_filter = ("grant__conference", "category")
+    search_fields = ("grant__full_name", "grant__email")
+    autocomplete_fields = ("grant",)
+
+
 @admin.register(Grant)
 class GrantAdmin(ExportMixin, ConferencePermissionMixin, admin.ModelAdmin):
     change_list_template = "admin/grants/grant/change_list.html"

backend/grants/migrations/0030_grantreimbursement_grant_reimbursement_categories.py

@@ -0,0 +1,34 @@
+# Generated by Django 5.1.4 on 2025-06-04 16:50
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('grants', '0029_grantreimbursementcategory'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='GrantReimbursement',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('granted_amount', models.DecimalField(decimal_places=0, help_text='Actual amount granted for this category', max_digits=6, verbose_name='granted amount')),
+                ('category', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='grants.grantreimbursementcategory', verbose_name='reimbursement category')),
+                ('grant', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='reimbursements', to='grants.grant', verbose_name='grant')),
+            ],
+            options={
+                'verbose_name': 'Grant Reimbursement',
+                'verbose_name_plural': 'Grant Reimbursements',
+                'ordering': ['grant', 'category'],
+                'unique_together': {('grant', 'category')},
+            },
+        ),
+        migrations.AddField(
+            model_name='grant',
+            name='reimbursement_categories',
+            field=models.ManyToManyField(related_name='grants', through='grants.GrantReimbursement', to='grants.grantreimbursementcategory'),
+        ),
+    ]

backend/grants/models.py

@@ -250,6 +250,10 @@ class ApprovedType(models.TextChoices):
         blank=True,
     )
 
+    reimbursement_categories = models.ManyToManyField(
+        GrantReimbursementCategory, through="GrantReimbursement", related_name="grants"
+    )
+
     objects = GrantQuerySet().as_manager()
 
     def __init__(self, *args, **kwargs):
@@ -370,6 +374,37 @@ def has_approved_accommodation(self):
         )
 
 
+class GrantReimbursement(models.Model):
+    """Links a Grant to its reimbursement categories and stores the actual amount granted."""
+
+    grant = models.ForeignKey(
+        Grant,
+        on_delete=models.CASCADE,
+        related_name="reimbursements",
+        verbose_name=_("grant"),
+    )
+    category = models.ForeignKey(
+        GrantReimbursementCategory,
+        on_delete=models.CASCADE,
+        verbose_name=_("reimbursement category"),
+    )
+    granted_amount = models.DecimalField(
+        _("granted amount"),
+        max_digits=6,
+        decimal_places=0,
+        help_text=_("Actual amount granted for this category"),
+    )
+
+    def __str__(self):
+        return f"{self.grant.full_name} - {self.category.name} - {self.granted_amount}"
+
+    class Meta:
+        verbose_name = _("Grant Reimbursement")
+        verbose_name_plural = _("Grant Reimbursements")
+        unique_together = [("grant", "category")]
+        ordering = ["grant", "category"]
+
+
 class GrantConfirmPendingStatusProxy(Grant):
     class Meta:
         proxy = True

backend/grants/tests/factories.py

@@ -2,7 +2,7 @@
 from factory.django import DjangoModelFactory
 
 from conferences.tests.factories import ConferenceFactory
-from grants.models import Grant, GrantReimbursementCategory
+from grants.models import Grant, GrantReimbursementCategory, GrantReimbursement
 from helpers.constants import GENDERS
 from users.tests.factories import UserFactory
 from countries import countries
@@ -75,3 +75,12 @@ def _create(self, model_class, *args, **kwargs):
             ParticipantFactory(user_id=grant.user.id, conference=grant.conference)
 
         return grant
+
+
+class GrantReimbursementFactory(DjangoModelFactory):
+    class Meta:
+        model = GrantReimbursement
+
+    grant = factory.SubFactory(GrantFactory)
+    category = factory.SubFactory(GrantReimbursementCategoryFactory)
+    granted_amount = factory.LazyAttribute(lambda obj: obj.category.max_amount)