Question

I’d like to implement a simple category system for my recipes.

Here’s my Recipe entity:

@PersistenceCapable
public class Recipe {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;
    @Persistent
    private List<Category> categories;

    public Recipe(List<Category> categories) {
        this.categories = categories;
    }
    ...
}

And my Category entity:

@PersistenceCapable
public class Category {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;
    @Persistent
    private String name;

    public Category(String name) {
        this.name = name;
    }
    ...
}

Now as you can see the association is simple. When I create a Recipe I make sure I construct it with a list of categories. This is great. On my site I can just iterate over a Recipe list (or whatever) and then just do .getCategories() on it to retrieve the categories I need.

However, say I want to retrieve all categories in the datastore and when I click on one category I want to be able to retrieve all recipes for that category. What’s the easiest to go about this?

To show all categories I have: select from Category.class group by name.
But how do I retrieve all the recipes under a given category? Is my design flawed for JDO?

Answer 1

SELECT FROM mydomain.Recipe WHERE category = :category

Don’t know what is this “flawed for JDO” idea … JDO simply provides transparent persistence and lets you design your classes as you want.