Data Loading DSL

Groovy man

Why?

Traditional approaches are cumbersome to create and maintain

Save time describing data to focus on tests

Traditional Approaches

SQL


		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');
		INSERT INTO foo VALUES('blah', 'blah', 'blah', 'blah');

Traditional Approaches

CSV


		'Header 1', 'Header 2', 'Header 3', 'Header 4', 'Header 5', 'Header 6'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'
		'blah', 'blah', 'blah', 'blah', 'blah', 'blah'

How to do better?

Leverage the stinkin JPA repositories

Groovy DSL will save lots of typing

Why Leverage JPA repositories

IDs can still be auto generated

Management of related entities is much easier

Possible Java Data Loading


public class MyAwesomeDataLoader implements ApplicationRunner {

	@Autowired
	private WidgetRepository widgetRepository;

	@Override
	public void run(ApplicationArguments args) throws Exception {
		widgetRepository.save(makeWidget("First!", "Secret");
		widgetRepository.save(makeWidget("Next One", "A follow up");
		// I'm tired of typing ...
	}

	private Widget makeWidget(String name, String importantAttribute) {
		Widget widget = new Widget();
		widget.setName(name);
		widget.setImportantAttribute(importantAttribute);
		return widget;
	}

}

Groovy DSL

Domain Specific Language

If you've used Gradle, you've used a DSL

DSL Magic

This


	plugins {
		id 'org.springframework.boot' version '1.5.7.RELEASE'
	}

Really Means This


	plugins({
		id('org.springframework.boot').version('1.5.7.RELEASE')
	})

DSL Magic

And This


	dependencies {
		// spring
		compile "org.springframework.boot:spring-boot-starter-web"
		compile "org.springframework.boot:spring-boot-starter-data-jpa"
	}

Really Means This


	dependencies({
		// spring
		compile("org.springframework.boot:spring-boot-starter-web")
		compile("org.springframework.boot:spring-boot-starter-data-jpa")
	})

Key DSL Elements

Method chains


		a b c d e => a(b).c(d).e


		a b c() d e => a(b).c().d(e)

Key DSL Elements

Closures

First class anonymous functions

Can control the delegate, the context object

What We're After


save widget { name 'First!' importantAttribute 'Secret' },
     widget { name 'Next One' importantAttribute 'A follow up' }

Two DSL Operations

Create an entity based on dynamic method name and closure

Save an entity using the appropriate repository

A class that loads and runs scripts


public class DataSeedRunner implements ApplicationRunner {
	public void run(ApplicationArguments args) throws Exception {
		// Locate all Groovy scripts under some base path
		// Parse each script with GroovyShell
		// Pass any necessary items to custom script class
		// Run the script
	}
}

A custom base Script class


public abstract class DataSeedScript extends Script {
    public Object invokeMethod(String name, Object args) {
		// Method to create entities
		// Lookup entity type based on name
		// Look for a Builder declared within entity type
		// Create a builder and pass it as delegate to the first argument which is a closure
		// Run the closure
		// Build entity with the builder
	}

	public List<Object> save(Object... entities) {
		// For each entity
		// Lookup the JPA repository per the entity's type
		// Use the repository to persist the entity
	}
}