Abstract Classes in GORM Relationships

Question

Grails GORM does not persist abstract domain classes to the database, causing a break in polymorphic relationships. For example:

abstract class User {
    String email
    String password
    static constraints = {
        email(blank:false, nullable:false,email:true)
        password(blank:false, password:true)
    }

    static hasMany = [membership:GroupMembership]
}

class RegularEmployee extends User {}

class Manager extends User {
    Workgroup managedGroup
}

class Document {
    String name
    String description
    int fileSize
    String fileExtension
    User owner
    Date creationTime
    Date lastModifiedTime
    DocumentData myData
    boolean isCheckedOut
    enum Sensitivity {LOW,MEDIUM,HIGH}
    def documentImportance = Sensitivity.LOW

    static constraints = {
        name(nullable:false, blank:false)
        description(nullable:false, blank:false)
        fileSize(nullable:false)
        fileExtension(nullable:false)
        owner(nullable:false)
        myData(nullable:false)
    }
}

causes

Caused by: org.hibernate.MappingException: An association from the table document refers to an unmapped class: User ... 25 more 2009-11-11 23:52:58,933 [main] ERROR mortbay.log - Nested in org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'messageSource': Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Invocation of init method failed; nested exception is org.hibernate.MappingException: An association from the table document refers to an unmapped class: User: org.hibernate.MappingException: An association from the table document refers to an unmapped class: User

But in this scenario, I want the polymorphic effects of allowing any user to own a document, while forcing every user of the system to fit into one of the defined roles. Hence, User should not be directly instantiated and is made abstract.

I don't want to use an enum for roles in a non-abstract User class, because I want to be able to add extra properties to the different roles, which may not make sense in certain contexts (I don't wanna have a single User with role set to RegularEmployee that somehow gets a not null managedGroup).

Is this a bug in Grails? Am I missing something?

I'm wondering what it would mean for an abstract class to be persisted to the DB, since there has to be something to persist (i.e., an instance). — Ben Dunlap
Well, I would venture that an abstract class is the preliminary schema outline, especially if it as at the root of an inheritance relationship. So if I have a User->RegularEmployee relationship, the table name should be User and a column should be added for "class", which is used to store the type a la the standard table-per-hierarchy model. — Visionary Software Solutions

Matt Lachman Matt Lachman · Accepted Answer · 2009-11-12T14:44:01

You might like to view the domain models for the Shiro, Nimble (uses Shiro), and/or Spring Security plugins. They create a concrete User domain and a concrete Role domain. Shiro in particular creates a UserRole domain for the many-to-many mapping.

Then on your Role domain, you can add whatever properties you want. If necessary, you can create a separate domain to allow for arbitrary properties like so:

class Role {
    //some properties
    static hasMany = [roleProperties:RoleProperty, ...]
}

class RoleProperty {
    String name
    String value
    static belongsTo = [role:Role]
}

I don't think you'll get what you're looking for in your current domain mapping though.

Abstract Classes in GORM Relationships

2 Answers