io.druid.server.lookup

Interface DataFetcher<K,V>

Type Parameters:

K - Keys type

V - Values type

All Known Implementing Classes:

JdbcDataFetcher

public interface DataFetcher<K,V>

This class will be used to pull data from a given lookup table.

Method Summary

Modifier and Type	Method and Description
Iterable<Map.Entry<K,V>>	fetch(Iterable<K> keys) Function used to perform a bulk lookup
V	fetch(K key) Function to perform a one item lookup.
Iterable<Map.Entry<K,V>>	fetchAll() Function used to fetch all the pair of key-values from the lookup One use case of this method is to populate a polling cache PollingCache
List<K>	reverseFetchKeys(V value) Function used to perform reverse lookup

Method Detail

fetchAll

Iterable<Map.Entry<K,V>> fetchAll()

Function used to fetch all the pair of key-values from the lookup One use case of this method is to populate a polling cache PollingCache

Returns:

Returns an Iterable of key-value pairs.

fetch

@Nullable
V fetch(K key)

Function to perform a one item lookup. For instance this can be used by a loading cache to fetch the value in case of the cache doesn't have it

Parameters:

key - non-null key used to lookup the value

Returns:

Returns null if the key doesn't have an associated value, or the value if it exists

fetch

Iterable<Map.Entry<K,V>> fetch(Iterable<K> keys)

Function used to perform a bulk lookup

Parameters:

keys - used to lookup the respective values

Returns:

Returns a Iterable containing the pair of existing key-value.

reverseFetchKeys

List<K> reverseFetchKeys(V value)

Function used to perform reverse lookup

Parameters:

value - use to fetch it's keys from the lookup table

Returns:

Returns a list of keys of the given value or an empty list Collections.EmptyList