Grails domain introduction

1. Grails - Domain Classes
Hiten Pratap Singh
hiten@nexthoughts.com
https://github.com/hitenpratap

2. Domain Classes
• Object oriented (OO) applications involve a domain model representing the
business entities that the application deals with.
• Domain classes has properties associated with them which map to a
database in order to persist instances of those classes.
• Domain class create : grails create-domain-class <<class_name>>

3. Persisting Fields to the Database
• All the fields in a domain class are persisted to the database.
• Each field in the class will map to a column in the database.

4. Validations
• Grails allows you to apply constraints to a domain class that can then be
used to validate a domain class instance.
• Constraints are applied using a "constraints" closure.
• To validate a domain class you can call the "validate()" method on an
instance.

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

6. Validating Constraints
def user = new User(params)
if(user.validate()){
//do something
}else{
user.errors.allErrors.each{
Println it
}
}

7. CustomValidators
class User {
static constraints = {
password(unique:true, length:5..15,
validator{val, obj >
if(val?.equalsIgnoreCase(obj.firstName)){
return false
}
})}}

8. Transient Properties
• Transient properties are never written to the database.
• Every property in a domain class is persistent and required.
• They don't have a corresponding column in the database.

9. Example
• class Company {
BigDecimal cash
BigDecimal receivables
BigDecimal getNetWorth() {
cash + receivables
}
static transients = ['netWorth']
}

10. Custom Mapping
class Person {
String firstName
String lastName
Integer age
static mapping = {
id column:'person_id'
firstName column:'person_first_name'
lastName column:'person_last_name'
age column:'person_age'
version false
}
}

11. Relationships
• Every table should have at least one relationship to another table.
• The types of relationships that Grails supports are:
• One-to-one
• One-to-many
• Many-to-one
• Many-to-many

12. One-to-One Relationship
class Car {
Engine engine
}
class Engine {
static belongsTo = [car:Car]
}

13. One-to-many relationships
class Artist {
String name
static hasMany = [albums:Album]
}

14. Many-to-many relationships
class Book {
static belongsTo = Author
static hasMany = [authors:Author]
}
class Author {
static hasMany = [books:Book]
}

15. Questions?

16. Hiten Pratap Singh
hiten@nexthoughts.com
https://github.com/hitenpratap