(Quick Reference) # 20.3 Adding Constraints Version: 3.2.8 ## 20.3 Adding Constraints You can still use GORM validation even if you use a Java domain model. Grails lets you define constraints through separate scripts in the `src/main/groovy/` directory. The script must be in a directory that matches the package of the corresponding domain class and its name must have a Constraints suffix. For example, if you had a domain class `org.example.Book`, then you would create the script `src/main/groovy/org/example/BookConstraints.groovy`\. Add a standard GORM `constraints` block to the script:
    constraints = {
        title blank: false
        author blank: false
    }
Once this is in place you can validate instances of your domain class! | Quick Reference (hide)