handle adding contributor that already exists

app/views/book.py

@@ -1,4 +1,4 @@
-from flask import Blueprint, render_template, flash, redirect, url_for
+from flask import Blueprint, render_template, flash, redirect, url_for, request
 from flask_login import login_required, current_user
 
 from app import models as m, db, forms as f
@@ -72,15 +72,22 @@ def add_contributor(book_id):
     form = f.AddContributorForm()
 
     if form.validate_on_submit():
+        book_contributor = m.BookContributor.query.filter_by(
+            user_id=form.user_id.data, book_id=book_id
+        ).first()
+        if book_contributor:
+            flash("Already exists!", "danger")
+            return redirect(url_for("book.settings", book_id=book_id))
+
         role = m.BookContributor.Roles(int(form.role.data))
         m.BookContributor(user_id=form.user_id.data, book_id=book_id, role=role).save()
 
         flash("Contributor was added!", "success")
-        return redirect(url_for("book.get_all"))
+        return redirect(url_for("book.settings", book_id=book_id))
     else:
         log(log.ERROR, "Book create errors: [%s]", form.errors)
         for field, errors in form.errors.items():
             field_label = form._fields[field].label.text
             for error in errors:
                 flash(error.replace("Field", field_label), "danger")
-        return redirect(url_for("book.get_all"))
+        return redirect(url_for("book.settings", book_id=book_id))

tests/test_book.py

@@ -88,6 +88,14 @@ def test_add_contributor(client: FlaskClient):
 
     assert response.status_code == 200
     assert b"Contributor was added!" in response.data
+    response: Response = client.post(
+        f"/book/{book.id}/add_contributor",
+        data=dict(user_id=moderator.id, role=m.BookContributor.Roles.MODERATOR),
+        follow_redirects=True,
+    )
+
+    assert response.status_code == 200
+    assert b"Already exists!" in response.data
 
     contributor: m.BookContributor = m.BookContributor.query.filter_by(
         user=moderator, book=book