Examples with ColumnSelectorStrategy org.apache.druid.query.dimension.ColumnSelectorStrategy used on opensource projects

Example 1 with ColumnSelectorStrategy

use of org.apache.druid.query.dimension.ColumnSelectorStrategy in project druid by druid-io.

the class DimensionHandlerUtils method createColumnSelectorPluses.

/**
 * Creates an array of ColumnSelectorPlus objects, selectors that handle type-specific operations within
 * query processing engines, using a strategy factory provided by the query engine. One ColumnSelectorPlus
 * will be created for each column specified in dimensionSpecs.
 * <p>
 * The ColumnSelectorPlus provides access to a type strategy (e.g., how to group on a float column)
 * and a value selector for a single column.
 * <p>
 * A caller should define a strategy factory that provides an interface for type-specific operations
 * in a query engine. See GroupByStrategyFactory for a reference.
 *
 * @param <Strategy>            The strategy type created by the provided strategy factory.
 * @param strategyFactory       A factory provided by query engines that generates type-handling strategies
 * @param dimensionSpecs        The set of columns to generate ColumnSelectorPlus objects for
 * @param columnSelectorFactory Used to create value selectors for columns.
 * @return An array of ColumnSelectorPlus objects, in the order of the columns specified in dimensionSpecs
 * @see ColumnProcessors#makeProcessor which may replace this in the future
 */
public static <Strategy extends ColumnSelectorStrategy> ColumnSelectorPlus<Strategy>[] createColumnSelectorPluses(ColumnSelectorStrategyFactory<Strategy> strategyFactory, List<DimensionSpec> dimensionSpecs, ColumnSelectorFactory columnSelectorFactory) {
    int dimCount = dimensionSpecs.size();
    @SuppressWarnings("unchecked") ColumnSelectorPlus<Strategy>[] dims = new ColumnSelectorPlus[dimCount];
    for (int i = 0; i < dimCount; i++) {
        final DimensionSpec dimSpec = dimensionSpecs.get(i);
        final String dimName = dimSpec.getDimension();
        final ColumnValueSelector<?> selector = getColumnValueSelectorFromDimensionSpec(dimSpec, columnSelectorFactory);
        Strategy strategy = makeStrategy(strategyFactory, dimSpec, columnSelectorFactory.getColumnCapabilities(dimSpec.getDimension()), selector);
        final ColumnSelectorPlus<Strategy> selectorPlus = new ColumnSelectorPlus<>(dimName, dimSpec.getOutputName(), strategy, selector);
        dims[i] = selectorPlus;
    }
    return dims;
}