Question

I’d like to version a grails domain class by DateTime such that:

• each primary ID + DateTime property results in a new DB row (i.e. a new DB row per version)
• the newest version can be found without having to specify the DateTime value

My knowledge of grails is a little limited right now and I don’t understand how I can achieve this.

Consider the following domain class as an example:

import org.joda.time.DateTime

class Page {
    String pageId
    DateTime theVersion
    String content

    static constraints = {
        pageId(nullable:false, blank:false, unique:true, matches:"[a-zA-Z\\._-]+")
        content(nullable:false, blank:false)
    }

    static mapping = {
        content(type:"text")
    }
}

• What changes are needed to ensure a new DB row is inserted per version?

  I’m assuming some form of constraint is required such that pageId+theVersion is unique but I don’t know how to express this in the GORM DSL.

• How might I get the most recent version without knowing the relevant DateTime value?

  I’m envisaging something like:
  Page.findByPageIdAndTheVersionLessThanEquals('uniquePageId', new DateTime())

  I expect this would find many objects not just one. I’d like to be able to also express the equivalent of ORDER BY theVersion DESC LIMIT 0,1

Answer 1

• Just create the new versions with new Page(), not with get() – a new record will be inserted.

To assure uniqueness, put into constraints:
theVersion(unique: 'pageId')

• Page.findByPageId(pageId, [sort: 'theVersion', order: 'desc', max: 1])

• You can utilize Grails’ dateCreated implicit timestamping feature – it will even work with joda-time plugin.

• OTOH, why don’t you utilize Grails’ built-in version field? It provides you some features out of box and takes care for optimistic locking.