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YAWP! postgresql
There is a newer version: 2.08alpha
package io.yawp.driver.postgresql;

import io.yawp.driver.api.QueryDriver;
import io.yawp.driver.postgresql.datastore.*;
import io.yawp.driver.postgresql.sql.ConnectionManager;
import io.yawp.repository.FutureObject;
import io.yawp.repository.IdRef;
import io.yawp.repository.Repository;
import io.yawp.repository.query.QueryBuilder;
import org.apache.commons.lang3.concurrent.ConcurrentUtils;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Future;

public class PGQueryDriver implements QueryDriver {

    private Repository r;

    private Datastore datastore;

    private EntityToObjectConverter toObject;

    public PGQueryDriver(Repository r, ConnectionManager connectionManager) {
        this.r = r;
        this.datastore = Datastore.create(connectionManager);
        this.toObject = new EntityToObjectConverter(r);
    }

    @SuppressWarnings("unchecked")
    @Override
    public  List objects(QueryBuilder builder) {
        try {
            List queryResult = generateResults(builder, false);

            List objects = new ArrayList();

            for (Entity entity : queryResult) {
                objects.add((T) toObject.convert(builder.getModel(), entity));
            }

            return objects;
        } catch (FalsePredicateException e) {
            return Collections.emptyList();
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public  List> ids(QueryBuilder builder) {
        try {
            List queryResult = generateResults(builder, false);

            List> ids = new ArrayList>();

            for (Entity entity : queryResult) {
                ids.add((IdRef) IdRefToKey.toIdRef(r, entity.getKey(), builder.getModel()));
            }

            return ids;
        } catch (FalsePredicateException e) {
            return Collections.emptyList();
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public  T fetch(IdRef id) {
        try {
            Key key = IdRefToKey.toKey(r, id);
            Entity entity = datastore.get(key);
            return (T) toObject.convert(id.getModel(), entity);
        } catch (EntityNotFoundException e) {
            return null;
        }
    }

    @Override
    public  FutureObject fetchAsync(IdRef id) {
        T object = fetch(id);
        Future futureObject = ConcurrentUtils.constantFuture(object);
        return new FutureObject(r, futureObject);
    }

    // query

    private List generateResults(QueryBuilder builder, boolean keysOnly) throws FalsePredicateException {
        return datastore.query(new Query(builder, keysOnly));
    }

}