org.dataloader

Interface BatchLoader<K,V>

Type Parameters:

K - type parameter indicating the type of keys to use for data load requests.

V - type parameter indicating the type of values returned

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
 @PublicSpi
public interface BatchLoader<K,V>

A function that is invoked for batch loading a list of data values indicated by the provided list of keys. The function returns a promise of a list of results of individual load requests.

There are a few constraints that must be upheld:

• The list of values must be the same size as the list of keys.
• Each index in the list of values must correspond to the same index in the list of keys.

For example, if your batch function was provided the list of keys:

  [
      2, 9, 6, 1
  ]
 

and loading from a back-end service returned this list of values:

  [
      { id: 9, name: 'Chicago' },
      { id: 1, name: 'New York' },
      { id: 2, name: 'San Francisco' },
  ]
 

then the batch loader function contract has been broken.

The back-end service returned results in a different order than we requested, likely because it was more efficient for it to do so. Also, it omitted a result for key 6, which we may interpret as no value existing for that key.

To uphold the constraints of the batch function, it must return a List of values the same length as the List of keys, and re-order them to ensure each index aligns with the original keys [ 2, 9, 6, 1 ]:

  [
      { id: 2, name: 'San Francisco' },
      { id: 9, name: 'Chicago' },
      null,
      { id: 1, name: 'New York' }
 ]
 

Method Summary

Modifier and Type	Method and Description
java.util.concurrent.CompletionStage<java.util.List<V>>	load(java.util.List<K> keys) Called to batch load the provided keys and return a promise to a list of values.

Method Detail

load

java.util.concurrent.CompletionStage<java.util.List<V>> load(java.util.List<K> keys)

Called to batch load the provided keys and return a promise to a list of values.

If you need calling context then implement BatchLoaderWithContext

Parameters:

keys - the collection of keys to load

Returns:

a promise of the values for those keys