argos/dmp-backend/web/src/main/java/eu/eudat/logic/managers/PaginationManager.java

package eu.eudat.logic.managers;

import eu.eudat.data.query.definition.TableQuery;
import eu.eudat.data.query.definition.helpers.ColumnOrderings;
import eu.eudat.data.query.definition.helpers.Ordering;
import eu.eudat.queryable.QueryableList;
import eu.eudat.queryable.queryableentity.DataEntity;

import java.util.Arrays;
import java.util.Collection;

public class PaginationManager {

    public static <T extends DataEntity> QueryableList<T> applyPaging(QueryableList<T> items, TableQuery tableRequest) throws Exception {
        if (tableRequest.getOrderings() != null) applyOrder(items, tableRequest);
        if (tableRequest.getLength() != null) items.take(tableRequest.getLength());
        if (tableRequest.getOffset() != null) items.skip(tableRequest.getOffset());
        if (tableRequest.getSelection() != null && tableRequest.getSelection().getFields() != null && tableRequest.getSelection().getFields().length > 0)
            items.withFields(Arrays.asList(tableRequest.getSelection().getFields()));
        return items;
    }

    public static <T extends DataEntity> void applyOrder(QueryableList<T> items, TableQuery tableRequest) throws Exception {
        ColumnOrderings columnOrderings = tableRequest.getOrderings();
        for (Ordering ordering : columnOrderings.getFieldOrderings()) {
            if (ordering.getOrderByType() == Ordering.OrderByType.ASC)
                applyAscOrder(items, ordering);
            if (ordering.getOrderByType() == Ordering.OrderByType.DESC) {
                applyDescOrder(items, ordering);
            }
        }
        return;
    }

    private static <T extends DataEntity> void applyAscOrder(QueryableList<T> items, Ordering ordering) {
        if (ordering.getColumnType() == Ordering.ColumnType.COUNT) {
            items.orderBy((builder, root) -> builder.asc(builder.size(root.<Collection>get(ordering.getFieldName()))));
        } else if (ordering.getColumnType() == Ordering.ColumnType.JOIN_COLUMN) {
            String[] fields = ordering.getFieldName().split(":");
            items.orderBy((builder, root) -> builder.asc(root.get(fields[0]).get(fields[1])));
        } else {
            items.orderBy((builder, root) -> builder.asc(root.get(ordering.getFieldName())));
        }
    }

    private static <T extends DataEntity> void applyDescOrder(QueryableList<T> items, Ordering ordering) {
        if (ordering.getColumnType() == Ordering.ColumnType.COUNT) {
            items.orderBy((builder, root) -> builder.desc(builder.size(root.<Collection>get(ordering.getFieldName()))));
        } else if (ordering.getColumnType() == Ordering.ColumnType.JOIN_COLUMN) {
            String[] fields = ordering.getFieldName().split(":");
            items.orderBy((builder, root) -> builder.desc(root.get(fields[0]).get(fields[1])));
        } else {
            items.orderBy((builder, root) -> builder.desc(root.get(ordering.getFieldName())));
        }
    }
}