## 7.1 Declaring Constraints

Within a domain class a constraints are defined with the constraints property that is assigned a code block:

    class User {
        String login
        String password
        String email
        Integer age    static constraints = {
    	  …
        }
    }

You then use method calls that match the property name for which the constraint applies in combination with named parameters to specify constraints:

    class User {
        ...    static constraints = {
            login(size:5..15, blank:false, unique:true)
            password(size:5..15, blank:false)
            email(email:true, blank:false)
            age(min:18, nullable:false)
        }
    }

In this example we've declared that the `login` property must be between 5 and 15 characters long, it cannot be blank and must be unique. We've all applied other constraints to the `password`, `email` and `age` properties.

> A complete reference for the available constraints can be found on the reference guide