java - Finding a list of related objects by ID

Question

Let's say for example I have a bridge table called PersonAnimal. I want to search for all the people who have a given animal's ID. The query so far looks like:

Animal animal = getById(Animal.class, animalId)
ObjectSelect
    .query(PersonAnimal.class)
    .where(PersonAnimal.ANIMAL.eq(animal))
    .select(context)

However the first line in the above code segment shows that I first have to retrieve the related object from the database. I want to get rid of that database lookup and instead do something like:

ObjectSelect
    .query(PersonAnimal.class)
    .where(PersonAnimal.ANIMAL_ID.eq(animalId)) // <- Find by ID instead
    .select(context)

Is that possible?

I am running version 4.1 of the Apache Cayenne ORM.

标签： javakotlinormapache-cayenne

Answer 1

就像我发布问题一样，我找到了答案。您需要Expression使用Property这样的对象创建一个：

val findByIdExpr = Property.create(PersonAnimal.ANIMAL.name, Long::class.java).eq(yourId)
val gotList = ObjectSelect
   .query(PersonAnimal.class)
   .where(findByIdExpr)
   .select(context)

上面的代码在 Kotlin 中，但从 Java 的角度来看也很容易理解。