Grails is a powerful web application framework based on the Groovy programming language. It leverages the principles of the Convention over Configuration (CoC) paradigm, making it easy to build web applications with minimal configuration. Grails is built on top of the Spring framework and integrates seamlessly with Hibernate for ORM (Object-Relational Mapping).

• Convention over Configuration: Reduces the need for extensive configuration files.
• DRY Principle: Encourages code reuse and reduces redundancy.
• Groovy-based: Leverages the dynamic features of Groovy.
• Spring and Hibernate Integration: Provides robust backend support.
• Scaffolding: Automatically generates CRUD operations for domain classes.
• Plugins: Extensible with a wide range of plugins.

• Java Development Kit (JDK) 8 or higher
• Groovy (optional, as Grails includes its own Groovy distribution)
• Grails framework

1. Download Grails: Visit the Grails website and download the latest version.
2. Set Environment Variables:
   • Add GRAILS_HOME environment variable pointing to the Grails installation directory.
   • Add Grails bin directory to the PATH environment variable.
3. Verify Installation:

   grails -version
   

1. Create a New Application:

   grails create-app myapp
   

   This command creates a new Grails application named myapp.

2. Navigate to the Application Directory:

   cd myapp
   

3. Run the Application:

   grails run-app
   

   This command starts the Grails development server. You can access the application at http://localhost:8080.

• grails-app: Contains the main application code.
  • controllers: MVC controllers.
  • domain: Domain classes (models).
  • services: Business logic.
  • views: GSP (Groovy Server Pages) views.
  • conf: Configuration files.
• src: Contains Groovy and Java source files.
• test: Contains test cases.
• build.gradle: Build configuration file.

• Constraints: Define validation rules for the fields.

This command generates controllers, views, and other necessary files for the Book domain class.

• Scaffold: Automatically generates CRUD actions.

1. Create a new Grails application named library.
2. Create a Book domain class with fields: title, author, and releaseDate.
3. Generate scaffolding for the Book domain class.
4. Run the application and test the CRUD operations.

1. Create Application:

   grails create-app library
   cd library
   

2. Create Domain Class:

   package library
   
   class Book {
       String title
       String author
       Date releaseDate
   
       static constraints = {
           title blank: false
           author blank: false
           releaseDate nullable: true
       }
   }
   

3. Generate Scaffolding:

   grails generate-all library.Book
   

4. Run Application:

   grails run-app
   

In this section, we introduced the Grails framework, set up the environment, and created a simple Grails application. We explored the application structure, created a domain class, and generated scaffolding for CRUD operations. Finally, we provided a practical exercise to reinforce the learned concepts. In the next module, we will delve into other Groovy libraries and tools that complement the Grails framework.