I have 4 classes like below:

from django.db import models

class A(models.Model):
    title = models.CharField(max_length=100)

class B(models.Model):
    title_b = models.CharField(max_length=100)
    a = models.ForeignKey(A, on_delete=models.CASCADE)

    class Meta:
        constraints = [
            models.UniqueConstraint(fields=['title_b'], name='unique_title_b')
        ]

class C(models.Model):
    title_c = models.CharField(max_length=100)
    a = models.ForeignKey(A, on_delete=models.CASCADE)

class D(models.Model):
    title_d = models.CharField(max_length=100)
    a = models.ForeignKey(A, on_delete=models.CASCADE)

All related classes are used as Inline model which described below:

from django.contrib import admin

class BInline(admin.TabularInline):
    model = B

class CInline(admin.TabularInline):
    model = C

class DInline(admin.TabularInline):
    model = D

And Model Admin of class A is defined as

class AAdmin(admin.ModelAdmin):
    inlines = [BInline, CInline, DInline]

As you can see class B has a constraint on title uniqueness. If I enter duplicate data for class B in admin panel, an Integrity Error is raised and error page with title IntegrityError at /app/A/81ac3366-4cdb-4cbb-a861-340ff188c760/change/
duplicate key value violates unique constraint “unique_title_b”
DETAIL: Key (title)=(TestDuplicate) already exists. is shown.
In order to show user a friendly message rather than this error page, I override save_related method in class AAdmin like below:

def save_related(self, request, form, formsets, change):
        try:
            with transaction.atomic():
                super().save_related(request, form, formsets, change)
        except IntegrityError as e:
            self.message_user(request, 'A related model constraint was violated: {}'.format(e), level=messages.ERROR)

I expect that after overriding save_related method, the error page doesn’t display anymore and user stays in the same change model page in admin panel; but error page still shows after I made these changes.
Can someone explain to me where did I go wrong in this?