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Gemasoft
Asked: 2020-01-26 15:02:47 +0800 CST 2020-01-26 15:02:47 +0800 CST

What is the difference between a Ref and a Key in Google Datastore?

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I started using Objectifyit as a library to work more comfortably with it Google Datastore, Google App Enginebut I have a doubt and I don't know the difference between using Refand Keyin the definition of properties of my entity.

For example:

@Entity
public class Car {

    @Id
    Long id;

    Key<User> driver;
}

either

@Entity
public class Car {

    @Id
    Long id;

    Ref<User> driver;
}

Apparently both generate a relationship with the User entity but I don't understand what the difference is between using one or the other since when making queries or inserting data they behave exactly the same.

Does anyone know what the fundamental difference is?

google-app-engine

2 Answers

  1. Best Answer

    The only difference between Key <>and Ref <>, is that the Ref <>is a container that also Key <>contains a reference to the actual entity. It does not hold real references, the value will come from the entity that has been previously loaded into the session cache.

    With Refand Load, you may have fewer calls to the database; It depends on your usage profile and the form of your data.

    • 1

  2. ref is a wrapper, which includes the key class and makes the call to load the corresponding entity, either from the cache or by reading the database.

    In most cases it is more comfortable to use Ref

    Here and here are a couple very detailed explanations of their differences and the behavior ofRef

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