org.apache.druid.query.lookup

Class LookupExtractor

java.lang.Object

org.apache.druid.query.lookup.LookupExtractor

Direct Known Subclasses:

MapLookupExtractor

public abstract class LookupExtractor
extends Object

Constructor Summary

Constructors

Constructor and Description
LookupExtractor()

Method Summary

Modifier and Type	Method and Description
abstract String	apply(String key) Apply a particular lookup methodology to the input string
Map<String,String>	applyAll(Iterable<String> keys)
abstract boolean	canIterate() Returns true if this lookup extractor's iterable() method will return a valid iterator.
abstract byte[]	getCacheKey() Create a cache key for use in results caching
boolean	isOneToOne()
abstract Iterable<Map.Entry<String,String>>	iterable() Returns an Iterable that iterates over the keys and values in this lookup extractor.
abstract List<String>	unapply(String value) Provide the reverse mapping from a given value to a list of keys
Map<String,List<String>>	unapplyAll(Iterable<String> values)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LookupExtractor

public LookupExtractor()

Method Detail

apply

@Nullable
public abstract String apply(@Nullable
                                       String key)

Apply a particular lookup methodology to the input string

Parameters:

key - The value to apply the lookup to.

Returns:

The lookup, or null when key is `null` or cannot have the lookup applied to it and should be treated as missing.

applyAll

public Map<String,String> applyAll(Iterable<String> keys)

Parameters:

keys - set of keys to apply lookup for each element

Returns:

Returns Map whose keys are the contents of keys and whose values are computed on demand using lookup function unapply(String) or empty map if values is `null` User can override this method if there is a better way to perform bulk lookup

unapply

public abstract List<String> unapply(@Nullable
                                     String value)

Provide the reverse mapping from a given value to a list of keys

Parameters:

value - the value to apply the reverse lookup

Returns:

the list of keys that maps to value or empty list. Note that for the case of a none existing value in the lookup we have to cases either return an empty list OR list with null element. returning an empty list implies that user want to ignore such a lookup value. In the other hand returning a list with the null element implies user want to map the none existing value to the key null. Null value maps to empty list.

unapplyAll

public Map<String,List<String>> unapplyAll(Iterable<String> values)

Parameters:

values - Iterable of values for which will perform reverse lookup

Returns:

Returns Map whose keys are the contents of values and whose values are computed on demand using the reverse lookup function unapply(String) or empty map if values is `null` User can override this method if there is a better way to perform bulk reverse lookup

canIterate

public abstract boolean canIterate()

Returns true if this lookup extractor's iterable() method will return a valid iterator.

iterable

public abstract Iterable<Map.Entry<String,String>> iterable()

Returns an Iterable that iterates over the keys and values in this lookup extractor.

Throws:

UnsupportedOperationException - if canIterate() returns false.

getCacheKey

public abstract byte[] getCacheKey()

Create a cache key for use in results caching

Returns:

A byte array that can be used to uniquely identify if results of a prior lookup can use the cached values

isOneToOne

public boolean isOneToOne()