Embedding should not be your default solution: in general, one-to-one is the way to go.
Embedding is used for when there are conventions used over and over again in the database. I've
seen dates stored as numbers "FOO_YR", "FOO_MON", "FOO_DAY", and currencies stored as "CENTS" and
"CURCODE" (value in minimum denominational unit and the currency code). While you theoretically
could manage that kind of structure through one-to-one mappings, you end up losing context and
meaning for those fields: the resulting table doesn't mean much, and the domain object *really*
doesn't mean anything.
An alternative solution to the embedding problem space is Hibernate User Types, but those are more
of a hassle than they're often worth.
~~ Robert.
bill.turner wrote:
> In Robert Fischer's book Grails Persistence with GORM and GSQL, he provides
> an example of embedding a class in a domain. In the example, he embeds class
> Name in class Foo. That example is fine as far as it goes, but because Name
> was defined in ./src/groovy, it is not a domain, thus constraints could not
> be defined within the class. Now, it may be possible to define constraints
> on the properties of the embedded from the parent (I have not tried, nor
> googled to find out), that is less than ideal if Name is likely to be
> embedded in several classes and the constraints should hold for all classes.
> If it is possible to define constraints for the class even though it is
> outside of the domain tree, please enlighten me.
>
> Searching for solutions, it seems that you can define the class to be
> embedded in ./grails-app/domain, giving you the ability to define
> constraints. The problem with this solution, as I understand it, is that if
> the embedded class is only and always used as an embedded class, a table
> will be created but no data ever written to it. This could be confusing for
> those that are unfamiliar with the idiosyncracies of Grails, especially
> those that hit the tables directly via sql or from some other non-Grails
> application.
>
> If my understanding is correct, then why would one ever embed? I cannot
> believe the peformance hit for joining two tables is that great in
> one-to-one relationships. Am I wrong about this?
>
> Thanks!
>
> -----
> Bill Turner
>
http://www.changent.com Groovy/Grails Talk
--
~~ Robert Fischer, Smokejumper IT Consulting.
Enfranchised Mind Blog
http://EnfranchisedMind.com/blogCheck out my book, "Grails Persistence with GORM and GSQL"!
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