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 an 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