Question

I need some help with a JDO query.

I have the following Entities:

recipe:

@PersistenceCapable
class Recipe{

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Long key;

    ...

    @Persistent(mappedBy = "recipe")
    private List<RecipeIngredient> ingredients
}

recipeIngredient:

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
class RecipeIngredient implements Serializable {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    Integer amount

    @Persistent
    Key unit

    @Persistent
    Key ingredient

    @Persistent
    Recipe recipe

ingredient:

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
class Ingredient implements Serializable {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    String name

A Recipe can have several recipeIngredients which holds the actual ingredient, the amount of the ingredient and the unit.

I would like to get all recipes by ingredients which only hold the given ingredients and not more.

At the moment I do this:

• get all ingredient objects by ingredient name
• get all recipeIngredient objects by ingredient key
• get all recipes by recipeIngredient
• check if all recipeIngredients from recipe are in recipeIngredient list from before
• if so add recipe to output list

Can I do this with a query? maybe something similar to having ?

Answer 1

Try something like…

select r from Recipe r
        where ingredients.contains(ri) && (ri.ingredient.name.matches(:searchTxt))

Also take a look at: http://www.datanucleus.org/servlet/forum/listthreads?forum=9

I don’t use Google App Engine but I do use DataNucleus heavily and I believe that DataNucleus is the implementation of JDO that the App Engine uses.

Let me know how this works on App Engine as I do this same kind of thing all the time in my apps.