diff --git a/expenses_manager/expenses/forms.py b/expenses_manager/expenses/forms.py
index b180361..51df4db 100644
--- a/expenses_manager/expenses/forms.py
+++ b/expenses_manager/expenses/forms.py
@@ -1,7 +1,17 @@
 from django import forms
-from .models import Expense
+from .models import Expense, Category
 
 class ExpenseForm(forms.ModelForm):
+    
+    def __init__(self, *args, **kwargs):
+        # Get user
+        user = kwargs.pop('user', None)
+        
+        super().__init__(*args, **kwargs)
+        
+        if user:
+            self.fields['category'].queryset = Category.objects.filter(owner=user)
+        
     class Meta:
         model = Expense
         fields = [
diff --git a/expenses_manager/expenses/models.py b/expenses_manager/expenses/models.py
index 6e3f82b..2a3abb6 100644
--- a/expenses_manager/expenses/models.py
+++ b/expenses_manager/expenses/models.py
@@ -4,8 +4,14 @@ from django.db.models.fields import related
 
 class Category(models.Model):
     name = models.CharField(max_length=100)
+    owner = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="categories",
+    )
+    
     parent = models.ForeignKey(
-        "self",
+        'self',
         on_delete=models.CASCADE,
         null=True,
         blank=True,
@@ -13,7 +19,7 @@ class Category(models.Model):
     )
     
     class Meta:
-        unique_together = ("name", "parent")
+        unique_together = ("name", "parent", "owner")
         verbose_name_plural = "categories"
     
     def __str__(self):
@@ -60,9 +66,7 @@ class Expense(models.Model):
     
     category = models.ForeignKey(
         Category,
-        on_delete=models.SET_NULL,
-        null=True,
-        blank=True,
+        on_delete=models.PROTECT,
         related_name="expenses",
     )
     
diff --git a/expenses_manager/expenses/views.py b/expenses_manager/expenses/views.py
index bacdb89..04e6f7d 100644
--- a/expenses_manager/expenses/views.py
+++ b/expenses_manager/expenses/views.py
@@ -1,7 +1,7 @@
+from .models import Expense
+from .forms import ExpenseForm
 from django.contrib.auth import login
 from django.utils.ipv6 import is_valid_ipv6_address
-from . models import Expense
-from .forms import ExpenseForm
 
 from django.shortcuts import get_object_or_404, render, redirect
 from django.contrib.auth.decorators import login_required
@@ -20,7 +20,7 @@ def expense_list(request):
 @login_required
 def expense_create(request):
     if request.method == "POST":
-        form = ExpenseForm(request.POST)
+        form = ExpenseForm(request.POST or None, user=request.user)
         if form.is_valid():
             expense = form.save(commit=False)
             expense.owner = request.user
@@ -28,7 +28,7 @@ def expense_create(request):
             form.save_m2m()
             return redirect('expense_list')
     else:
-        form = ExpenseForm()
+        form = ExpenseForm(user=request.user)
     
     return render(
         request,
@@ -45,12 +45,12 @@ def expense_edit(request, pk):
         owner=request.user,
     )
     if request.method == "POST":
-        form = ExpenseForm(request.POST, instance=expense)
+        form = ExpenseForm(request.POST or None, instance=expense, user=request.user)
         if form.is_valid():
             expense = form.save()
             return redirect('expense_list')
     else:
-        form = ExpenseForm(instance=expense)
+        form = ExpenseForm(instance=expense, user=request.user)
     
     return render(
         request,