There is a master-detail relationship between two objects and I want to ensure that the master object should not have more than 10 child records. How can we achieve this without using a trigger ?
Create Roll-up summary - COUNT field on Parent object and validation rule
If you’re trying to enforce a record limit of 25 on the parent roll-up summary field, create validation rules on your child objects. When you add a child record, your validation rule on the child object can check if the count is already 25 or greater.
from documentation - Best Practices