Overview of Grails Object Relational Mapping (GORM)
•
2 likes•1,796 views
GORM is Grails' object relational mapping tool that provides a simpler and easier to use API for working with databases compared to Hibernate. It leverages Hibernate under the hood but uses conventions over configuration, allowing database access and relationships to be defined directly in domain classes without additional mapping files or DAOs. While powerful, GORM has some limitations like lack of support for multiple data sources and disadvantages of programming in a dynamic language.
Report
Share
Overview of Grails Object Relational Mapping (GORM)
- 1. Overview of GORM Chris Richardson Author of POJOs in Action www.chrisrichardson.net
- 2. About Chris Grew up in England and live in Oakland, CA Over 20+ years of software development experience including 12 years of Java Author of POJOs in Action Speaker at JavaOne, SpringOne, NFJS, JavaPolis, Spring Experience, etc. Chair of the eBIG Java SIG in Oakland (www.ebig.org) Run the Groovy/Grails meetup (http://java.meetup.com/161) Run a consulting and training company that u co su t g a d t a g co pa y t at helps organizations build better software faster and deploy it on Amazon EC2 Founder of Cloud Tools, an open-source project for deploying Java applications on Amazon EC2: http://code.google.com/p/cloudtools http://code google com/p/cloudtools Founder of a startup that provides outsourced, automated, and Java-centric datacenter management on the cloud: www.cloudfoundry.com y Slide 2 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 3. What’s GORM? GORM = Grails Object Relational Mapping Built B ilt on Hibe nate Hibernate Leverages the power of Hibernate But is very different - simpler, easier to use API y p, Uses convention over configuration Defaults for which classes to persist Defaults for their O/R mapping Leverages the meta-object protocol Adds persistence methods to domain classes p No equivalent of Hibernate Session Avoids the need for dependency injection Eliminates many DAO cookie-cutter methods Slide 3 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 4. Database access made easy y class Customer { String name g } Customer c = new Customer(quot;John Doequot;) Ct Ct (quot;J h D quot;) if (!c.save()) fail quot;validation failed: ${c.errors}quot; Customer c2 = Customer.get(c.id) No dependency injection c2.delete() assertNull Customer.get(c.id) def customers = Customer findAllByName(“Fred”) Customer.findAllByName( Fred ) Slide 4 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 5. Relationships don’t have to be difficult class Customer { static hasMany = [ accounts : Account] } class Account { static belongsTo = [customer: Customer] double balance } Customer c = <…> Account a = new Account(…) c.addToAccounts(a) assertSame c, a.customer assertTrue c.accounts.contains(a) Slide 5 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 6. When the defaults aren’t right g class Customer { static transients = [quot;networthquot;] [ ] static mapping = { id column: 'customer_id' table 'crc_customer' _ columns { name column: 'customer_name' } } def getNetworth() { …} … } Slide 6 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 7. Working with constraints g class Customer { static constraints = { name(size: 5..15, blank: false) } String name } Checked by the UI Checked by save() Used by GORM to generate schema constraints Slide 7 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 8. More on dynamic finders y Rich query language Various methods: fi dB () fi dAllB () Vi th d findBy…(), findAllBy…(), countBy…() Various operators: e.g findAllByFirstNameAndLastName(…), findAllByBalanceLessThan(…), findAllByStatusIsNotNull() y () BUT: Limited to single class/table, i.e. no joins Lack of encapsulation – the name of the finder reflects the implementation – not the meaning Slide 8 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 9. When dynamic finders are insufficient HQL List accounts = Account.findAll(“from Account where balance < ?”, [threshold]) def c = Account.createCriteria() def results = c.list { lt( balance lt(“balance”, threshold) } Slide 9 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 10. Mapping with XML or annotations pp g Using .hbm.xml files Create grails- app/conf/hibernate/hibernate.cfg.xml Define .hbm.xml mapping files D fi hb l i fil Map either Groovy or Java classes Using JPA annotations Ui t ti Annotate Java classes Create hib C hibernate.cfg.xml f l You can still use the dynamically defined d fi d GORM methods i G th d in Groovy Slide 10 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 11. Under the covers Creates DataSource specified in grails- app/config/DataSource.groovy Creates Hibernate SessionFactory Use ExpandoMetaClass mechanism Add persistence methods, e.g. domainClass.metaClass.'static'.get = {…} Adds methodMissing() to handle dynamic finders fi d These methods have a reference to the SessionFactory Slide 11 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 12. GORM is great but … g GORM does not support multiple DataSources Lack of SOC Data access logic is scattered around the application rather than being encapsulated by DAOs CoC-based mapping works best for new databases Disadvantages of programming in a dynamic language Slide 12 Copyright (c) 2009 Chris Richardson. All rights reserved.
- 13. Further reading g My ACM Queue article: http://queue.acm.org/detail.cfm?id=1394140 Slide 13 Copyright (c) 2009 Chris Richardson. All rights reserved.