CODEWITHSUNDEEP
grailsgrails-ormderived
mzuba
mzuba

Reputation: 1275

Grails: derived fields in domain classes

Suppose I have a domain class branch which has several members:

…
static hasMany = [ members:Member ];
…

Now suppose I want to have the number of members of that branch readily available, to have it displayed in the list and view actions, so perhaps storing that information into a variable in the domain class itself would be a good idea?

…
Integer memberCount = members.size();
static constraints = {
    memberCount(editable:false);
}
…

(Is this the correct syntax?) Edit: This is not the correct syntax. I cannot assess the size of the members list, as it doesn’t exist yet and grails will complain about size() not being applicable to null objects. What else could I try?

However, as memberCount is now a variable in the domain class, it is possible to assign a value to it upon creation of the Branch (which is contra-intuitive) and it will not be updated automatically once a new Member is added.

It is of course possible to reach the desired result in a different way. I could manipulate the view.gsp and list.gsp in the /Branch directory, add some additional <td>s there etc. But that does not seem very elegant to me.

Basically, I think what I am looking for is some way to tell grails that a certain variable is derived, should not be setable by the user, but update whenever necessary. Is there such way?

Upvotes: 0

Views: 2661

Answers (1)

OverZealous
OverZealous

Reputation: 39580

You can add any property you don't want persisted to the transients static list:

static transients = ['memberCount']

See this page in the manual

Also, this StackOverflow question answers the same question

Also, a better way to do derived properties may be to use the Derived Properties feature of GORM

Upvotes: 2

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