Package org.apache.solr.response.transform

Interface TransformerFactory.FieldRenamer

All Known Implementing Classes:

GeoTransformerFactory, RawValueTransformerFactory

Enclosing class:

TransformerFactory

public static interface TransformerFactory.FieldRenamer

The TransformerFactory.FieldRenamer interface should be implemented by any TransformerFactory capable of generating transformers that might rename fields, and should implement create(String, SolrParams, SolrQueryRequest, Map, Set) in place of TransformerFactory.create(String, SolrParams, SolrQueryRequest) (with the latter method overridden to throw UnsupportedOperationException).

DocTransformers returned via create(String, SolrParams, SolrQueryRequest, Map, Set) will be added in a second pass, allowing simplified logic in TransformerFactory.create(String, SolrParams, SolrQueryRequest) for non-renaming factories.

create(String, SolrParams, SolrQueryRequest, Map, Set) must implement extra logic to be aware of preceding field renames, and to make subsequent TransformerFactory.FieldRenamer transformers aware of its own field renames.

It is harmless for a DocTransformer that does _not_ in practice rename fields to be returned from a factory that implements this interface (e.g., for conditional renames?); but doing so opens the possibility of create(String, SolrParams, SolrQueryRequest, Map, Set) being called _after_ fields have been renamed, so such implementations must still check whether the field with which they are concerned has been renamed ... and if it _has_, must copy the field back to its original name. This situation also demonstrates the motivation for separating the creation of DocTransformers into two phases: an initial phase involving no field renames, and a subsequent phase that implement extra logic to properly handle field renames.

Method Summary

Modifier and Type	Method	Description
DocTransformer	create(String field, SolrParams params, SolrQueryRequest req, Map<String,String> renamedFields, Set<String> reqFieldNames)	Analogous to TransformerFactory.create(String, SolrParams, SolrQueryRequest), but to be implemented by TransformerFactorys that produce DocTransformers that may rename fields.
default boolean	mayModifyValue()	Returns true if implementations of this class may (even subtly) modify field values.

Method Detail

create

DocTransformer create(String field,
                      SolrParams params,
                      SolrQueryRequest req,
                      Map<String,String> renamedFields,
                      Set<String> reqFieldNames)

Analogous to TransformerFactory.create(String, SolrParams, SolrQueryRequest), but to be implemented by TransformerFactorys that produce DocTransformers that may rename fields.

Parameters:

field - The destination field

params - Local params associated with this transformer (e.g., source field)

req - The current request

renamedFields - Maps source=>dest renamed fields. Implementations should check this first, updating their own "source" field(s) as necessary, and if renaming (not copying) fields, should also update this map with the implementations "own" introduced source=>dest field mapping

reqFieldNames - Set of explicitly requested field names; implementations should consult this set to determine whether it's appropriate to rename (vs. copy) a field (e.g.: boolean copy = reqFieldNames != null && reqFieldNames.contains(sourceField) )

Returns:

A transformer to be used in processing field values in returned documents.

mayModifyValue

default boolean mayModifyValue()

Returns true if implementations of this class may (even subtly) modify field values. (GeoTransformerFactory may do this, e.g.). To fail safe, the default implementation returns true. This method should be overridden to return false if the implementing class is guaranteed to not modify any values for the fields that it renames.