如何遍历2个单向Ebean rels @ManyToOne和@OneToOne

Question

Didn't find the answer around here. I have 3 objects (only showing relevant parts):

@Entity 
class Module {
} 

@Entity
class FeaturedModule {
    @OneToOne(optional = false)
    public Module playModule;

    public static final Finder<Long, FeaturedModule> FIND = new Finder<Long, FeaturedModule>(Long.class, FeaturedModule.class);
}

@Entity
class ModuleVersion {
    @ManyToOne
    public Module playModule

    public static final Finder<Long, ModuleVersion> FIND = new Finder<Long, ModuleVersion>(Long.class, ModuleVersion.class);
}

The rels are unidirectional, that is, Module has no reference to the other 2 entities.

Questions:

1. How to find (from ModuleVersion) Modules not within a rel with FeaturedModules
2. How to find (from FeaturedModules) a series of FeaturedModules with a given ModuleVersion

Answer 1

In very general: it's good idea to add a Boolean flag to the Module model, thanks to this, you don't need to write sophisticated queries for finding modules containing relations, you can just check the flag:

public static List<Module> findAllFeatured() {
    return find.select("id,name").where().eq("isFeatured", true).findList();
}

public static List<Module> findAllNotFeatured() {
    // give here list of field to select WITHOUT featured, otherwise it will 
    // create a JOIN to featured which will result that you will be not able
    // to get records without associations
    return find.select("id, name").where().eq("isFeatured", false).findList();
} 

using the isFeatured flag you're able to filter ModuleVersion s as well easily:

public static List<ModuleVersion> findAll(String version) {
    return find.fetch("module").where().like("version", version).findList();
}

public static List<ModuleVersion> findFeatured(String version) {
    return find.fetch("module")
            .where().like("version", version).eq("module.isFeatured", true).findList();
}

public static List<ModuleVersion> findNotFeatured(String version) {
    return find.fetch("module")
            .where().like("version", version).eq("module.isFeatured", false).findList();
}

Of course for 'automatic' setting the flag you should override save() and update(Object o) methods in your Module model, let me know if you need a sample for this.