GORM is Grails’ object relational mapping (ORM) implementation, which sits on top of the very popular Hibernate framework. If you are familliar with Hibernate then understanding GORM will be easy. GORM is very straightForward and easy to learn.

ORM frameworks objective is to present an API where you can just think and program in objects, and the underlying framework will handle how to interface with the relational database.
Configuration:
Grails have by default database configuration already so that you could start coding your business logic right away. By default, it uses embedded H2 database. You can change this configuration if you want in Datasource.groovy file, as shown below:
dataSource {
pooled = true
driverClassName = “com.mysql.jdbc.Driver”
dialect = “org.hibernate.dialect.MySQL5InnoDBDialect”
}

As GORM is ORM so corresponding table will be created automatically for all your domain classes. You don’t have to create the tables manually in your database or write an sql statement for this.

When tables are created you can start with CRUD part.

Lets take an example of Project class:
class Project{
String name;

}

Create operation:
Project p = new Project()
p.name = “Project_1″
p.save()

or you can do as following also:
Project p = new Project(name:”Project_1″).save()

Read operation:
Following code retrieves row of table Project with id=’12’.
Project p = Project.get(12);

Update operation:
To perform update operation you can do following :
Project p = Project.get(12)
p.name = “Project_New”
p.save()

Delete operation:
To delete a row just invoke delete() on instance to delete as shown below:
Project p = Project.get(12)
p.delete()

With GORM writing of business logic becomes very easy and convenient .

ProsperaSoft offers Grails development solutions. You can email at info@prosperasoft.com to get in touch with ProsperaSoft Grails experts and consultants.

Joins are very important when you need to retrieve data from two or more tables based on some condition. In Grails, you can use HQL queries to perform join operations. We have executeQuery to perform joins in grails.

Lets take an example to show how joins can be performed with One-to-Many relationship:

Suppose there are classes Project and Task.

class Project {
     static hasMany = [tasks:Task]
     String name
}

class Task{
        static belongsTo = Project 
       Project project
       String name
}

Assume we have inserted following data:

class BootStrap {
def init = { servletContext ->
if ( Project .count() == 0 ) {
Project prj_1= new Project (name:’Project_1′).save()
new Task(project:prj_1, name:’Task_1′).save()
new Task(project:prj_1, name:’Task_2′).save()
Project prj_2= new Project (name:’Project_2′).save()
new Task(project:prj_2, name:’Task_3′).save()
new Task (project:prj_2, name:’Task_4′).save()
Project prj_3 = new Project (name:’Project_3′).save()
new Task(project:prj_3 , name:’Task_5′).save()
new Task(project:prj_3 , name:’Task_6′).save()
}
}
def destroy = {
}
}

Here, are some problems where we need to retrieve data from both tables and we are going to use joins:

Problem 1. Which Project does Task Task_3 belong?

def result = Project.executeQuery(
“select p from Project p join p.tasks pt where pt.name = ‘Task_3′”)
result.each { project ->
println “Project is ${project.name}”
}

Output will be “Project is Project_1″

Problem 2. How many tasks does Project_3 have?

def result = Project.executeQuery(
“select count(*) from Project p join p.tasks pt where p.name = ‘Project_3′”)
println “${result[0]}”

Output will be “2” as we have 2 tasks for Project_3.

Problem 3. How many tasks does each project have?

def result = Project.executeQuery(
“select p.name, count(*) from Project p join p.tasks pt group by p”)
result.each { item ->
println “Project ${item[0]} has ${item[1]} tasks”
}

Output will be as shown below:

Project  Project_1 has 2 tasks
Project  Project_2 has 2 tasks
Project  Project_3 has 2 tasks

We can perform Join without having any relationship between tables.

ProsperaSoft offers Grails development solutions. You can email at info@prosperasoft.com to get in touch with ProsperaSoft Grails experts and consultants.