static constraints = { login size : 5 .. 15 , blank : false , unique : true password size : 5 .. 15 , blank : false email email : true , blank : false age min : 18

Refer to the user guide topic on Constraints for more information.

Global Constraints

You can apply constraints globally inside grails-app/conf/runtime.groovy as follows:

grails.gorm.default.constraints = {
    '*'(nullable: true, size: 1..20)
The wildcard signifies that the constraints apply to all properties. You can also define shared constraints:
grails.gorm.default.constraints = {
    myShared(nullable: true, size: 1..20)
That can be reused in your class:
class User {
    static constraints = {
        login(shared: "myShared")
Sharing Constraints
Global constraints are one way of sharing constraints between different classes, for example between a domain class and a command object. This is no longer the only way. Grails 2 introduces a new syntax for the constraints block that allows you to reuse constraints directly from another class.
Let’s say you have a domain class like so:
class User {
    String firstName
    String lastName
    String passwordHash
    static constraints = {
        firstName blank: false, nullable: false
        lastName blank: false, nullable: false
        passwordHash blank: false, nullable: false
You then want to create a command object, UserCommand, that shares some of the properties of the domain class and the corresponding constraints. You do this with the importFrom() method:
class UserCommand {
    String firstName
    String lastName
    String password
    String confirmPassword
    static constraints = {
        importFrom User
        password blank: false, nullable: false
        confirmPassword blank: false, nullable: false
This will import all the constraints from the User domain class and apply them to UserCommand. The import will ignore any constraints in the source class (User) that don’t have corresponding properties in the importing class (UserCommand). In the above case, only the 'firstName' and 'lastName' constraints will be imported into UserCommand.
If you want more control over which constraints are imported, use the include and exclude named arguments. Both of these accept a list of simple or regular expression strings that are matched against the property names in the source constraints. So for example, if you only wanted to import the 'lastName' constraint you would use:
static constraints = {
    importFrom User, include: ["lastName"]
or if you wanted all constraints that ended with 'Name':
static constraints = {
    importFrom User, include: [/.*Name/]
Of course, exclude does the reverse, specifying which constraints should not be imported.
Quick Reference
creditCard
Validates that a String value is a valid credit card number
cardNumber(creditCard: true)
email
Validates that a String value is a valid email address.
homeEmail(email: true)
inList
Validates that a value is within a range or collection of constrained values.
name(inList: ["Joe", "Fred", "Bob"])
matches
Validates that a String value matches a given regular expression.
login(matches: "[a-zA-Z]+")
Validates that a value does not exceed the given maximum value.
age(max: new Date()) price(max: 999F)
maxSize
Validates that a value’s size does not exceed the given maximum value.
children(maxSize: 25)
Validates that a value does not fall below the given minimum value.
age(min: new Date()) price(min: 0F)
minSize
Validates that a value’s size does not fall below the given minimum value.
children(minSize: 25)
notEqual
Validates that that a property is not equal to the specified value
login(notEqual: "Bob")
nullable
Allows a property to be set to null - defaults to false.
age(nullable: true)
range
Uses a Groovy range to ensure that a property’s value occurs within a specified range
age(range: 18..65)
scale
Set to the desired scale for floating point numbers (i.e., the number of digits to the right of the decimal point).
salary(scale: 2)
Uses a Groovy range to restrict the size of a collection or number or the length of a String.
children(size: 5..15)
unique
Constrains a property as unique at the database level
login(unique: true)
Validates that a String value is a valid URL.
homePage(url: true)
validator
Adds custom validation to a field.
See documentation
display
Boolean that determines whether the property is displayed in the scaffolding views. If true (the default), the property is displayed.
editable
Boolean that determines whether the property can be edited from the scaffolding views. If false, the associated form fields are displayed in read-only mode.
format
Specify a display format for types that accept one, such as dates. For example, 'yyyy-MM-dd'.
password
Boolean indicating whether this is property should be displayed with a password field. Only works on fields that would normally be displayed with a text field.
widget
Controls what widget is used to display the property. For example, 'textarea' will force the scaffolding to use a <textArea> tag.
    static constraints = {
        firstName blank: false, nullable: false
        middleName blank: true, nullable: true
In the example above, accessing User.constrainedProperties.firstName.blank would yield false, while
User.constrainedProperties.middleName.blank would yield true.
Command Objects
Accessing the constraints on a command object is slightly different. You can access a command object’s constraints programmatically in another context by accessing the constraintsMap static property of a class that implements Validateable. That property is an instance of Map<String, ConstrainedProperty>
class User implements Validateable {
    String firstName
    String middleName
    static constraints = {
        firstName blank: false, nullable: false
        middleName blank: true, nullable: true
In the example above, accessing User.constraintsMap.firstName.blank would yield false, while
User.constraintsMap.middleName.blank would yield true.