graphql.extensions.ExtensionsMerger Maven / Gradle / Ivy
package graphql.extensions;
import graphql.PublicSpi;
import org.jetbrains.annotations.NotNull;
import java.util.Map;
/**
* This interface is a callback asking code to merge two maps with an eye to creating
* the graphql `extensions` value.
*
* How best to merge two maps is hard to know up front. Should it be a shallow clone or a deep one,
* should keys be replaced or not and should lists of value be combined? The {@link ExtensionsMerger} is the
* interface asked to do this.
*
* This interface will be called repeatedly for each change that has been added to the {@link ExtensionsBuilder} and it is expected to merge the two maps as it sees fit
*/
@PublicSpi
public interface ExtensionsMerger {
/**
* A default implementation will do the following
*
* - It will deep merge the maps
* - It concatenate lists when they occur under the same key
* - It will add any keys from the right hand side map that are not present in the left
* - If a key is in both the left and right side, it will prefer the right hand side
* - It will try to maintain key order if the maps are ordered
*
*/
ExtensionsMerger DEFAULT = new DefaultExtensionsMerger();
/**
* Called to merge the map on the left with the map on the right according to whatever code strategy some-one might envisage
*
* The map on the left is guaranteed to have been encountered before the map on the right
*
* @param leftMap the map on the left
* @param rightMap the map on the right
*
* @return a non null merged map
*/
@NotNull
Map merge(@NotNull Map leftMap, @NotNull Map rightMap);
}