HierarchySiblingActionHandler.java

package my.bookshop.handlers;

import static cds.gen.adminservice.AdminService_.GENRE_HIERARCHY;

import cds.gen.adminservice.AdminService_;
import cds.gen.adminservice.GenreHierarchy;
import cds.gen.adminservice.GenreHierarchyMoveSiblingContext;
import cds.gen.adminservice.GenreHierarchy_;
import com.sap.cds.ql.Select;
import com.sap.cds.ql.Update;
import com.sap.cds.services.handler.EventHandler;
import com.sap.cds.services.handler.annotations.On;
import com.sap.cds.services.handler.annotations.ServiceName;
import com.sap.cds.services.persistence.PersistenceService;
import java.util.List;
import org.springframework.stereotype.Component;

@Component
@ServiceName(AdminService_.CDS_NAME)
/** Example of a custom handler for nextSiblingAction */
public class HierarchySiblingActionHandler implements EventHandler {

  private final PersistenceService db;

  HierarchySiblingActionHandler(PersistenceService db) {
    this.db = db;
  }

  @On
  void onMoveSiblingAction(GenreHierarchy_ ref, GenreHierarchyMoveSiblingContext context) {
    // Find current node and its parent
    GenreHierarchy toMove =
        db.run(Select.from(ref).columns(c -> c.ID(), c -> c.parent_ID())).single();

    // Find all children of the parent, which are siblings of the entry being moved
    List<GenreHierarchy> siblingNodes =
        db.run(
                Select.from(GENRE_HIERARCHY)
                    .columns(c -> c.ID(), c -> c.siblingRank())
                    .where(c -> c.parent_ID().eq(toMove.getParentId())))
            .list();

    int oldPosition = 0;
    int newPosition = siblingNodes.size();
    for (int i = 0; i < siblingNodes.size(); ++i) {
      GenreHierarchy sibling = siblingNodes.get(i);
      if (sibling.getId().equals(toMove.getId())) {
        oldPosition = i;
      }
      if (context.getNextSibling() != null
          && sibling.getId().equals(context.getNextSibling().getId())) {
        newPosition = i;
      }
    }

    // Move siblings
    siblingNodes.add(
        oldPosition < newPosition ? newPosition - 1 : newPosition,
        siblingNodes.remove(oldPosition));

    // Recalculate ranks
    for (int i = 0; i < siblingNodes.size(); ++i) {
      siblingNodes.get(i).setSiblingRank(i);
    }

    // Update DB
    db.run(Update.entity(GENRE_HIERARCHY).entries(siblingNodes));
    context.setCompleted();
  }
}