> Markdown version of [Using JDBC with Lazy Query Container and FilteringTable](https://vaadin.com/docs/v7/framework/articles/UsingJDBCwithLazyQueryContainerAndFilteringTable). Section index: [llms.txt](https://vaadin.com/docs/v7/framework/llms.txt)

# <a id="using-jdbc-with-lazy-query-container-and-filteringtable"></a>Using JDBC with Lazy Query Container and FilteringTable

Introduction

Populating display tables from a database is a deceptively complicated operation, especially when mixing multiple techniques together. This page provides an example of one way to efficiently load data from a SQL database table into a filterable UI, using the *Lazy Query Container* and *FilteringTable* add-ons.

Note: Do not use the SQLContainer package. This is buggy and will have your database and garbage collector crunching in loops.

`Query` and `QueryFactory` implementation

The place to start is the Lazy Query Container’s (LQC) Query interface. This is where the interface with your database happens. This example access a database table with computer statistics. It’s read-only. How to log and access your JDBC connection differs in each environment; they are treated generically here. Only select imports are included.

```java
import org.vaadin.addons.lazyquerycontainer.Query;
import org.vaadin.addons.lazyquerycontainer.QueryDefinition;
import org.vaadin.addons.lazyquerycontainer.QueryFactory;

import com.vaadin.data.Container.Filter;
import com.vaadin.data.Item;
import com.vaadin.data.util.ObjectProperty;
import com.vaadin.data.util.PropertysetItem;
import com.vaadin.data.util.sqlcontainer.query.generator.StatementHelper;
import com.vaadin.data.util.sqlcontainer.query.generator.filter.QueryBuilder;

/**
 * Query for using the database's device-status table as a data source
 * for a Vaadin container (table).
 */
public class DeviceStatusQuery implements Query {
  private static  final Logger log = LoggerFactory.getLogger(DeviceStatusQuery.class);

  /**
   * The table column names. Use these instead of typo-prone magic strings.
   */
  public static enum Column {
    hostname, loc_id, update_when, net_ip, lan_ip, lan_mac, hardware,
    opsys, image, sw_ver, cpu_load, proc_count, mem_usage, disk_usage;

    public boolean is(Object other) {
      if (other instanceof String)
        return this.toString().equals(other);
      else
        return (this == other);
    }
  };

  public static class Factory implements QueryFactory {
    private int locId;

    /**
     * Constructor
     * @param locId - location ID
     */
    public Factory(int locId) {
      this.locId = locId;
    }

    @Override
    public Query constructQuery(QueryDefinition def) {
      return new DeviceStatusQuery(def, locId);
    }
  }//class Factory

  /////// INSTANCE ///////

  private String countQuery;
  private String fetchQuery;
  /** Borrow from SQLContainer to build filter queries */
  private StatementHelper stmtHelper = new StatementHelper();

  /**
   * Constructor
   * @param locId - location ID
   * @param userId - ID of user viewing the data
   */
  private DeviceStatusQuery(QueryDefinition def, int locId) {
    Build filters block List<Filter> filters = def.getFilters();
    String filterStr = null;
    if (filters != null && !filters.isEmpty())
      filterStr = QueryBuilder.getJoinedFilterString(filters, "AND", stmtHelper);

    // Count query
    StringBuilder query = new StringBuilder( "SELECT COUNT(*) FROM device_status");
    query.append(" WHERE loc_id=").append(locId);

    if (filterStr != null)
      query.append(" AND ").append(filterStr);

    this.countQuery = query.toString();

    // Fetch query
    query = new StringBuilder(
      "SELECT hostname, loc_id, update_when, net_ip, lan_ip, " +
      "lan_mac, hardware, opsys, image, sw_ver, cpu_load, " +
      "proc_count, mem_usage, disk_usage FROM device_status");
    query.append(" WHERE loc_id=").append(locId);

    if (filterStr != null)
      query.append(" AND ").append(filterStr);

    // Build Order by
    Object[] sortIds = def.getSortPropertyIds();
    if (sortIds != null && sortIds.length > 0) {
      query.append(" ORDER BY ");
      boolean[] sortAsc = def.getSortPropertyAscendingStates();
      assert sortIds.length == sortAsc.length;

      for (int si = 0; si < sortIds.length; ++si) {
        if (si > 0) query.append(',');

        query.append(sortIds[si]);
        if (sortAsc[si]) query.append(" ASC");
        else query.append(" DESC");
      }
    }
    else query.append(" ORDER BY hostname");

    this.fetchQuery = query.toString();

    log.trace("DeviceStatusQuery count: {}", this.countQuery);
    log.trace("DeviceStatusQuery fetch: {}", this.fetchQuery);
  }//constructor

  @Override
  public int size() {
    int result = 0;
    try (Connection conn = Database.getConnection()) {
      PreparedStatement stmt = conn.prepareStatement(this.countQuery);
      stmtHelper.setParameterValuesToStatement(stmt);
      ResultSet rs = stmt.executeQuery();
      if (rs.next()) result = rs.getInt(1);

      stmt.close();
    }
    catch (SQLException ex) {
      log.error("DB access failure", ex);
    }

    log.trace("DeviceStatusQuery size=\{}", result);
    return result;
  }

  @Override
  public List<Item> loadItems(int startIndex, int count) {
    List<Item> items = new ArrayList<Item>();
    try (Connection conn = Database.getConnection()) {
      String q = this.fetchQuery + " LIMIT " + count + " OFFSET " + startIndex;
      PreparedStatement stmt = conn.prepareStatement(q);
      stmtHelper.setParameterValuesToStatement(stmt);

      ResultSet rs = stmt.executeQuery();
      while (rs.next()) {
        PropertysetItem item = new PropertysetItem();
        // Include the data type parameter on ObjectProperty any time the value could be null
        item.addItemProperty(Column.hostname,
          new ObjectProperty<String>(rs.getString(1), String.class));
        item.addItemProperty(Column.loc_id,
          new ObjectProperty<Integer>(rs.getInt(2), Integer.class));
        item.addItemProperty(Column.update_when,
          new ObjectProperty<Timestamp>(rs.getTimestamp(3), Timestamp.class));
        item.addItemProperty(Column.net_ip,
          new ObjectProperty<String>(rs.getString(4)));
        item.addItemProperty(Column.lan_ip,
          new ObjectProperty<String>(rs.getString(5)));
        item.addItemProperty(Column.lan_mac,
          new ObjectProperty<String>(rs.getString(6)));
        item.addItemProperty(Column.hardware,
          new ObjectProperty<String>(rs.getString(7)));
        item.addItemProperty(Column.opsys,
          new ObjectProperty<String>(rs.getString(8)));
        item.addItemProperty(Column.image,
          new ObjectProperty<String>(rs.getString(9)));
        item.addItemProperty(Column.sw_ver,
          new ObjectProperty<String>(rs.getString(10)));
        item.addItemProperty(Column.cpu_load,
          new ObjectProperty<String>(rs.getString(11)));
        item.addItemProperty(Column.proc_count,
          new ObjectProperty<Integer>(rs.getInt(12)));
        item.addItemProperty(Column.mem_usage,
          new ObjectProperty<Integer>(rs.getInt(13)));
        item.addItemProperty(Column.disk_usage,
          new ObjectProperty<Integer>(rs.getInt(14)));

        items.add(item);
      }
      rs.close();
      stmt.close();
    }
    catch (SQLException ex) {
      log.error("DB access failure", ex);
    }

    log.trace("DeviceStatusQuery load {} items from {}={} found", count,
        startIndex, items.size());
    return items;
  } //loadItems()

/**
 * Only gets here if loadItems() fails, so return an empty state.
 * Throwing from here causes an infinite loop.
 */
 @Override
 public Item constructItem() {
  PropertysetItem item = new PropertysetItem();
  item.addItemProperty(Column.hostname, new ObjectProperty<String>(""));
  item.addItemProperty(Column.loc_id, new ObjectProperty<Integer>(-1));
  item.addItemProperty(Column.update_when,
    new ObjectProperty<Timestamp>(new Timestamp(System.currentTimeMillis())));
  item.addItemProperty(Column.net_ip, new ObjectProperty<String>(""));
  item.addItemProperty(Column.lan_ip, new ObjectProperty<String>(""));
  item.addItemProperty(Column.lan_mac, new ObjectProperty<String>(""));
  item.addItemProperty(Column.hardware, new ObjectProperty<String>(""));
  item.addItemProperty(Column.opsys, new ObjectProperty<String>(""));
  item.addItemProperty(Column.image, new ObjectProperty<String>(""));
  item.addItemProperty(Column.sw_ver, new ObjectProperty<String>(""));
  item.addItemProperty(Column.cpu_load, new ObjectProperty<String>(""));
  item.addItemProperty(Column.proc_count, new ObjectProperty<Integer>(0));
  item.addItemProperty(Column.mem_usage, new ObjectProperty<Integer>(0));
  item.addItemProperty(Column.disk_usage, new ObjectProperty<Integer>(0));

  log.warn("Shouldn't be calling DeviceStatusQuery.constructItem()");
    return item;
  }

  @Override
  public boolean deleteAllItems() {
    throw new UnsupportedOperationException();
  }

  @Override
  public void saveItems(List<Item> arg0, List<Item> arg1, List<Item> arg2) {
    throw new UnsupportedOperationException();
  }
}
```

Using the Query with FilteringTable

Now that we have our Query, we need to create a table to hold it. Here’s one of many ways to do it with FilteringTable.

```java
import org.tepi.filtertable.FilterDecorator;
import org.tepi.filtertable.numberfilter.NumberFilterPopupConfig;
import org.vaadin.addons.lazyquerycontainer.LazyQueryContainer;

import com.vaadin.data.Property;
import com.vaadin.server.Resource;
import com.vaadin.shared.ui.datefield.Resolution;
import com.vaadin.ui.DateField;
import com.vaadin.ui.AbstractTextField.TextChangeEventMode;

/**
 * Filterable table of device statuses.
 */
public class DeviceStatusTable extends FilterTable {
  private final
  String[] columnHeaders = {"Device", "Site", "Last Report", "Report IP",
      "LAN IP", "MAC Adrs", "Hardware", "O/S", "Image", "Software", "CPU"
      "Load", "Processes", "Memory Use", "Disk Use"};

  /**
   * Configuration this table for displaying of DeviceStatusQuery data.
   */
  public void configure(LazyQueryContainer dataSource) {
    super.setFilterGenerator(new LQCFilterGenerator(dataSource));
    super.setFilterBarVisible(true);
    super.setSelectable(true);
    super.setImmediate(true);
    super.setColumnReorderingAllowed(true);
    super.setColumnCollapsingAllowed(true);
    super.setSortEnabled(true);

    dataSource.addContainerProperty(Column.hostname, String.class, null, true, true);
    dataSource.addContainerProperty(Column.loc_id, Integer.class, null, true, false);
    dataSource.addContainerProperty(Column.update_when, Timestamp.class, null, true, true);
    dataSource.addContainerProperty(Column.net_ip, String.class, null, true, true);
    dataSource.addContainerProperty(Column.lan_ip, String.class, null, true, true);
    dataSource.addContainerProperty(Column.lan_mac, String.class, null, true, true);
    dataSource.addContainerProperty(Column.hardware, String.class, null, true, true);
    dataSource.addContainerProperty(Column.opsys, String.class, null, true, true);
    dataSource.addContainerProperty(Column.image, String.class, null, true, true);
    dataSource.addContainerProperty(Column.sw_ver, String.class, null, true, true);
    dataSource.addContainerProperty(Column.cpu_load, String.class, null, true, true);
    dataSource.addContainerProperty(Column.proc_count, Integer.class, null, true, true);
    dataSource.addContainerProperty(Column.mem_usage, Integer.class, null, true, true);
    dataSource.addContainerProperty(Column.disk_usage, Integer.class, null, true, true);

    super.setContainerDataSource(dataSource);
    super.setColumnHeaders(columnHeaders);
    super.setColumnCollapsed(Column.lan_mac, true);
    super.setColumnCollapsed(Column.opsys, true);
    super.setColumnCollapsed(Column.image, true);
    super.setFilterFieldVisible(Column.loc_id, false);
  }

  @Override
  protected String formatPropertyValue(Object rowId, Object colId, Property<?> property) {
    if (Column.loc_id.is(colId)) {
      // Example of how to translate a column value
      return Hierarchy.getLocation(((Integer) property.getValue())).getShortName();
    } else if (Column.update_when.is(colId)) {
      // Example of how to format a value.
      return ((java.sql.Timestamp) property.getValue()).toString().substring(0, 19);
    }

    return super.formatPropertyValue(rowId, colId, property);
  }

  /**
   * Filter generator that triggers a refresh of a LazyQueryContainer
   * whenever the filters change.
   */
  public class LQCFilterGenerator implements FilterGenerator {
    private final LazyQueryContainer lqc;

    public LQCFilterGenerator(LazyQueryContainer lqc) {
      this.lqc = lqc;
    }

    @Override
    public Filter generateFilter(Object propertyId, Object value) {
      return null;
    }

    @Override
    public Filter generateFilter(Object propertyId, Field<?> originatingField) {
      return null;
    }

    @Override
    public AbstractField<?> getCustomFilterComponent(Object propertyId) {
      return null;
    }

    @Override
    public void filterRemoved(Object propertyId) {
      this.lqc.refresh();
    }

    @Override
    public void filterAdded(Object propertyId, Class<? extends Filter> filterType, Object value) {
      this.lqc.refresh();
    }

    @Override
    public Filter filterGeneratorFailed(Exception reason, Object propertyId, Object value) {
      return null;
    }
  }
}
```

Put them together on the UI

Now we have our Container that reads from the database, and a Table for displaying them, lets put the final pieces together somewhere in some UI code:

```java
final DeviceStatusTable table = new DeviceStatusTable();
table.setSizeFull();

DeviceStatusQuery.Factory factory = new DeviceStatusQuery.Factory(locationID);
final LazyQueryContainer statusDataContainer = new LazyQueryContainer(factory,
  /*index*/ null, /*batchSize*/ 50, false);
statusDataContainer.getQueryView().setMaxCacheSize(300);
table.configure(statusDataContainer);

layout.addComponent(table);
layout.setHeight(100f, Unit.PERCENTAGE); // no scrollbar

// Respond to row click
table.addValueChangeListener(new Property.ValueChangeListener() {
  @Override
  public void valueChange(ValueChangeEvent event) {
    Object index = event.getProperty().getValue();
    if (index != nulll) {
      int locId = (Integer) statusDataContainer.getItem(index)
          .getItemProperty(DeviceStatusQuery.Column.loc_id).getValue();
      doSomething(locId);
      table.setValue(null); //visually deselect
    }
  }
});
```

And finally, since we’re using `SQLContainer`'s `QueryBuilder`, depending on your database you may need to include something like this once during your application startup:

```java
import com.vaadin.data.util.sqlcontainer.query.generator.filter.QueryBuilder;
import com.vaadin.data.util.sqlcontainer.query.generator.filter.StringDecorator;

// Configure Vaadin SQLContainer to work with MySQL
QueryBuilder.setStringDecorator(new StringDecorator("`","`"));
```