Package 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

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method 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