Easy Object Select

This page demonstrates selecting from a more complex model - a list of objects from the database.
This is easy to achieve using SelectModelFactory and a custom ValueEncoder, and together
they allow us to avoid storing the list of objects in the session and avoid rebuilding the list on submit.
Person: You chose:
In this example we feed a list of Persons (from the database) into SelectModelFactory to produce a SelectModel.
We tell it to use firstName as the option label.
We want the option value to be the person's id so we provide PersonEncoder, which converts between a Person, server-side, and their id, for client-side.
Note that PersonEncoder goes to the database when it converts an id to a Person, but this happens only on submit, and only for the chosen person.

References: Select, Using Select with a List, SelectModel, SelectModelFactory, ValueEncoder, EventContext, How To Select With Objects.

Home

The source for @EJB handling, etc. is shown in the @EJB example.

EasyObjectSelect.tml


<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!-- We need a doctype to allow us to use special characters like &nbsp; 
     We use a "strict" DTD to make IE follow the alignment rules. -->
     
<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_3.xsd">
<head>
    <link rel="stylesheet" type="text/css" href="${context:css/examples/examples.css}"/>
</head>
<body>
    <h1>Easy Object Select</h1>
    
    This page demonstrates selecting from a more complex model - a list of objects from the database.<br/>
    This is easy to achieve using <strong>SelectModelFactory</strong> and a custom <strong>ValueEncoder</strong>, and together <br/>
    they allow us to avoid storing the list of objects in the session and avoid rebuilding the list on submit.

    <div class="eg">
        <form t:type="form">
            Person: <select t:type="select" t:model="personsModel" t:value="person" t:encoder="personEncoder"></select>
            <input type="submit" value="Submit"/>
            You chose: ${person}
        </form>
    </div>
    
    In this example we feed a list of Persons (from the database) into SelectModelFactory to produce a SelectModel.<br/>
    We tell it to use firstName as the option label. <br/>
    We want the option value to be the person's id so we provide PersonEncoder, which converts between a Person, server-side, and their id, for client-side.<br/>
    Note that PersonEncoder goes to the database when it converts an id to a Person, but this happens only on submit, and only for the chosen person.<br/><br/>

    References:
    <a href="http://tapestry.apache.org/5.3/apidocs/org/apache/tapestry5/corelib/components/Select.html">Select</a>,
    <a href="http://tapestry.apache.org/using-select-with-a-list.html">Using Select with a List</a>, 
    <a href="http://tapestry.apache.org/5.3/apidocs/org/apache/tapestry5/SelectModel.html">SelectModel</a>, 
    <a href="http://tapestry.apache.org/5.3/apidocs/org/apache/tapestry5/services/SelectModelFactory.html">SelectModelFactory</a>,  
    <a href="http://tapestry.apache.org/5.3/apidocs/org/apache/tapestry5/ValueEncoder.html">ValueEncoder</a>,  
    <a href="http://tapestry.apache.org/5.3/apidocs/org/apache/tapestry5/EventContext.html">EventContext</a>, 
    <a href="http://wiki.apache.org/tapestry/Tapestry5HowtoSelectWithObjects">How To Select With Objects</a>.<br/><br/>
    
    <a t:type="pagelink" t:page="Index" href="#">Home</a><br/><br/>
    
    The source for @EJB handling, etc. is shown in the @EJB example.<br/><br/>
    
    <t:sourcecodedisplay src="/web/src/main/java/jumpstart/web/pages/examples/select/EasyObjectSelect.tml"/>
    <t:sourcecodedisplay src="/web/src/main/java/jumpstart/web/pages/examples/select/EasyObjectSelect.java"/>
    <t:sourcecodedisplay src="/web/src/main/java/jumpstart/web/css/examples/examples.css"/>
    <t:sourcecodedisplay src="/web/src/main/java/jumpstart/web/encoders/examples/PersonEncoder.java"/>
    <t:sourcecodedisplay src="/business/src/main/java/jumpstart/business/domain/person/PersonFinderService.java"/>
    <t:sourcecodedisplay src="/business/src/main/java/jumpstart/business/domain/person/Person.java"/>
</body>
</html>

EasyObjectSelect.java


package jumpstart.web.pages.examples.select;

import java.util.List;

import javax.ejb.EJB;

import jumpstart.business.domain.person.Person;
import jumpstart.business.domain.person.iface.IPersonFinderServiceLocal;
import jumpstart.web.encoders.examples.PersonEncoder;

import org.apache.tapestry5.EventContext;
import org.apache.tapestry5.SelectModel;
import org.apache.tapestry5.annotations.Property;
import org.apache.tapestry5.ioc.annotations.Inject;
import org.apache.tapestry5.services.SelectModelFactory;

public class EasyObjectSelect {
    static private final int MAX_RESULTS = 30;

    // The activation context

    private Long personId;

    // Screen fields

    @Property
    private SelectModel personsModel;

    @Property
    private Person person;

    // Generally useful bits and pieces

    @Inject
    private SelectModelFactory selectModelFactory;

    @EJB
    private IPersonFinderServiceLocal personFinderService;

    // The code

    Long onPassivate() {
        return personId;
    }

    void onActivate(EventContext context) {
        if (context.getCount() > 0) {
            personId = context.get(Long.class, 0);
        }
    }

    void onPrepareForRender() {
        // Get all persons - ask business service to find them (from the database)
        List<Person> persons = personFinderService.findPersons(MAX_RESULTS);

        if (personId != null) {
            person = findPersonInList(personId, persons);
        }

        personsModel = selectModelFactory.create(persons, "firstName");
    }

    void onValidateFromForm() {
        personId = person == null ? null : person.getId();
    }

    private Person findPersonInList(Long personId, List<Person> persons) {
        for (Person person : persons) {
            if (person.getId().equals(personId)) {
                return person;
            }
        }
        return null;
    }

    public PersonEncoder getPersonEncoder() {
        return new PersonEncoder(personFinderService);
    }

}

examples.css


body            { font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 13px; font-weight: normal; color: #333; line-height: 17px; }
h1              { font-size: 26px; line-height: 20px; } /* For IE 7 */
form            { margin: 0; }                  

.eg             { margin: 20px 0; padding: 20px; color: #888; 
                    border: 1px solid #ddd; border-radius: 4px; -webkit-border-radius: 4px; -mox-border-radius: 4px; }

a               { text-decoration: none; color: #3D69B6; }
a:hover         { text-decoration: underline; }

/* For BeanDisplay */
.eg dl          { margin: 0; color: #333; }
.eg dl.t-beandisplay dd.id  { display: inline; margin-left: 0px; }  /* IE 7 hack */

PersonEncoder.java


package jumpstart.web.encoders.examples;

import jumpstart.business.domain.person.Person;
import jumpstart.business.domain.person.iface.IPersonFinderServiceLocal;

import org.apache.tapestry5.ValueEncoder;

public class PersonEncoder implements ValueEncoder<Person> {

    private IPersonFinderServiceLocal personFinderService;

    public PersonEncoder(IPersonFinderServiceLocal personFinderService) {
        this.personFinderService = personFinderService;
    }

    @Override
    public String toClient(Person value) {
        return String.valueOf(value.getId());
    }

    @Override
    public Person toValue(String id) {
        return personFinderService.findPerson(Long.parseLong(id));
    }

}

PersonFinderService.java


package jumpstart.business.domain.person;

import java.util.Arrays;
import java.util.List;

import javax.ejb.Local;
import javax.ejb.Remote;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import jumpstart.business.domain.person.iface.IPersonFinderServiceLocal;
import jumpstart.business.domain.person.iface.IPersonFinderServiceRemote;
import jumpstart.util.query.SortCriterion;

@Stateless
@Local(IPersonFinderServiceLocal.class)
@Remote(IPersonFinderServiceRemote.class)
public class PersonFinderService implements IPersonFinderServiceLocal, IPersonFinderServiceRemote {

    @PersistenceContext(unitName = "jumpstart")
    private EntityManager em;

    public Person findPerson(Long id) {
        return em.find(Person.class, id);
    }

    public long countPersons() {
        return (Long) em.createQuery("select count(p) from Person p").getSingleResult();
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersons(int maxResults) {
        return em.createQuery("select p from Person p order by lower(p.firstName), lower(p.lastName)")
                .setMaxResults(maxResults).getResultList();
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersons(String partialName, int maxResults) {
        String searchName = partialName == null ? "" : partialName.toLowerCase();

        StringBuilder buf = new StringBuilder();
        buf.append("select p from Person p");
        buf.append(" where lower(firstName) like :firstName");
        buf.append(" or lower(lastName) like :lastName");
        buf.append(" order by lower(p.firstName), lower(p.lastName)");

        Query q = em.createQuery(buf.toString());
        q.setParameter("firstName", "%" + searchName + "%");
        q.setParameter("lastName", "%" + searchName + "%");

        List<Person> l = q.setMaxResults(maxResults).getResultList();
        return l;
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersonsByFirstName(String firstName) {
        String searchName = firstName == null ? "" : firstName.trim().toLowerCase();

        StringBuilder buf = new StringBuilder();
        buf.append("select p from Person p");
        buf.append(" where lower(p.firstName) = :searchName");
        buf.append(" order by lower(p.firstName), lower(p.lastName)");

        Query q = em.createQuery(buf.toString());
        q.setParameter("searchName", searchName);

        List<Person> l = q.getResultList();
        return l;
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersonsByLastName(String lastName) {
        String searchName = lastName == null ? "" : lastName.trim().toLowerCase();

        StringBuilder buf = new StringBuilder();
        buf.append("select p from Person p");
        buf.append(" where lower(p.lastName) = :searchName");
        buf.append(" order by lower(p.lastName), lower(p.firstName)");

        Query q = em.createQuery(buf.toString());
        q.setParameter("searchName", searchName);

        List<Person> l = q.getResultList();
        return l;
    }

    public long countPersons(String partialName) {
        return (Long) findPersons(true, partialName, 0, 0);
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersons(String partialName, int startIndex, int maxResults) {
        return (List<Person>) findPersons(false, partialName, startIndex, maxResults);
    }

    @SuppressWarnings("unchecked")
    private Object findPersons(boolean counting, String partialName, int startIndex, int maxResults) {
        String searchName = partialName == null ? "" : partialName.toLowerCase();

        StringBuilder buf = new StringBuilder();

        if (counting) {
            buf.append("select count(p) from Person p");
        }
        else {
            buf.append("select p from Person p");
        }
        buf.append(" where lower(firstName) like :firstName");
        buf.append(" or lower(lastName) like :lastName");

        if (!counting) {
            buf.append(" order by lower(p.firstName), lower(p.lastName)");
        }

        Query q = em.createQuery(buf.toString());
        q.setParameter("firstName", "%" + searchName + "%");
        q.setParameter("lastName", "%" + searchName + "%");

        if (counting) {
            Long qty = (Long) q.getSingleResult();
            return qty;
        }
        else {
            List<Person> l = q.setFirstResult(startIndex).setMaxResults(maxResults).getResultList();
            return l;
        }
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersons(int startIndex, int maxResults, List<SortCriterion> sortCriteria) {
        final List<String> PROPERTIES_TO_LOWER_FOR_SORT = Arrays.asList("firstName", "lastName");

        // Here we use JPQL. An alternative is to use javax.persistence.criteria.CriteriaQuery. For an example see
        // Tapestry's JpaGridDataSource.

        StringBuilder buf = new StringBuilder();
        buf.append("select p from Person p");
        buf.append(" order by ");

        boolean firstOrderByItem = true;
        boolean orderByIncludesId = false;

        for (SortCriterion sortCriterion : sortCriteria) {
            String propertyName = sortCriterion.getPropertyName();

            // Append an "order by" item, eg. "startDate", or ", lower(firstName) desc".

            if (!firstOrderByItem) {
                buf.append(", ");
            }
            if (PROPERTIES_TO_LOWER_FOR_SORT.contains(propertyName)) {
                buf.append("lower(").append(propertyName).append(")");
            }
            else {
                buf.append(propertyName);
            }
            buf.append(sortCriterion.getSortDirection().toStringForJpql());

            // We need to know later whether the "order by" includes id.

            if (propertyName.equals("id")) {
                orderByIncludesId = true;
            }
            firstOrderByItem = false;
        }

        // Ensure sequence is predictable by ensuring a unique property, id, is in the "order by".

        if (!orderByIncludesId) {
            if (!firstOrderByItem) {
                buf.append(", ");
            }
            buf.append("id");
        }

        Query q = em.createQuery(buf.toString());

        List<Person> l = q.setFirstResult(startIndex).setMaxResults(maxResults).getResultList();
        return l;
    }

    public long countPersons(String firstNameStartsWith, String lastNameStartsWith, Regions region) {
        return (Long) findPersons(true, firstNameStartsWith, lastNameStartsWith, region, 0, 0, null);
    }

    @SuppressWarnings("unchecked")
    public List<Person> findPersons(String firstNameStartsWith, String lastNameStartsWith, Regions region,
            int startIndex, int maxResults, List<SortCriterion> sortCriteria) {
        return (List<Person>) findPersons(false, firstNameStartsWith, lastNameStartsWith, region, startIndex,
                maxResults, sortCriteria);
    }

    @SuppressWarnings("unchecked")
    private Object findPersons(boolean counting, String firstNameStartsWith, String lastNameStartsWith, Regions region,
            int startIndex, int maxResults, List<SortCriterion> sortCriteria) {
        final List<String> PROPERTIES_TO_LOWER_FOR_SORT = Arrays.asList("firstName", "lastName");

        String searchFirstName = firstNameStartsWith == null ? "" : firstNameStartsWith.toLowerCase();
        String searchLastName = lastNameStartsWith == null ? "" : lastNameStartsWith.toLowerCase();

        StringBuilder buf = new StringBuilder();

        if (counting) {
            buf.append("select count(p) from Person p");
        }
        else {
            buf.append("select p from Person p");
        }

        buf.append(" where lower(firstName) like :firstName");
        buf.append(" and lower(lastName) like :lastName");
        if (region != null) {
            buf.append(" and region = :region");
        }

        if (!counting) {
            buf.append(" order by ");

            boolean firstOrderByItem = true;
            boolean orderByIncludesId = false;

            for (SortCriterion sortCriterion : sortCriteria) {
                String propertyName = sortCriterion.getPropertyName();

                // Append an "order by" item, eg. "startDate", or ", lower(firstName) desc".

                if (!firstOrderByItem) {
                    buf.append(", ");
                }
                if (PROPERTIES_TO_LOWER_FOR_SORT.contains(propertyName)) {
                    buf.append("lower(").append(propertyName).append(")");
                }
                else {
                    buf.append(propertyName);
                }
                buf.append(sortCriterion.getSortDirection().toStringForJpql());

                // We need to know later whether the "order by" includes id.

                if (propertyName.equals("id")) {
                    orderByIncludesId = true;
                }
                firstOrderByItem = false;
            }

            // Ensure sequence is predictable by ensuring a unique property, id, is in the "order by".

            if (!orderByIncludesId) {
                if (!firstOrderByItem) {
                    buf.append(", ");
                }
                buf.append("id");
            }
        }

        Query q = em.createQuery(buf.toString());
        q.setParameter("firstName", searchFirstName + "%");
        q.setParameter("lastName", searchLastName + "%");
        if (region != null) {
            q.setParameter("region", region);
        }

        if (counting) {
            Long qty = (Long) q.getSingleResult();
            return qty;
        }
        else {
            List<Person> l = q.setFirstResult(startIndex).setMaxResults(maxResults).getResultList();
            return l;
        }
    }

}

Person.java


package jumpstart.business.domain.person;

import java.io.Serializable;
import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EnumType;
import javax.persistence.Enumerated;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.Version;


/**
 * The Person entity.
 */
@Entity
@SuppressWarnings("serial")
public class Person implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(nullable = false)
    private Long id;

    @Version
    @Column(nullable = false)
    private Integer version;

    @Column(length = 10, nullable = false)
    private String firstName;

    @Column(length = 10, nullable = false)
    private String lastName;
    
    @Enumerated(EnumType.STRING)
    private Regions region;

    @Temporal(TemporalType.DATE)
    private Date startDate;

    public String toString() {
        final String DIVIDER = ", ";
        
        StringBuilder buf = new StringBuilder();
        buf.append(this.getClass().getSimpleName() + ": ");
        buf.append("[");
        buf.append("id=" + id + DIVIDER);
        buf.append("version=" + version + DIVIDER);
        buf.append("firstName=" + firstName + DIVIDER);
        buf.append("lastName=" + lastName + DIVIDER);
        buf.append("region=" + region + DIVIDER);
        buf.append("startDate=" + startDate);
        buf.append("]");
        return buf.toString();
    }

    // Default constructor is required by EJB3.
    public Person() {
    }

    public Person(String firstName, String lastName, Regions region, Date startDate) {
        super();
        this.firstName = firstName;
        this.lastName = lastName;
        this.region = region;
        this.startDate = startDate;
    }

    // The need for an equals() method is discussed at http://www.hibernate.org/109.html
    
    @Override
    public boolean equals(Object obj) {
        return (obj == this) || (obj instanceof Person) && id != null && id.equals(((Person) obj).getId());
    }

    // The need for a hashCode() method is discussed at http://www.hibernate.org/109.html

    @Override
    public int hashCode() {
        return id == null ? super.hashCode() : id.hashCode();
    }

    @PrePersist
    @PreUpdate
    public void validate() throws ValidationException {

        // Validate syntax...

        if ((firstName == null) || (firstName.trim().length() == 0)) {
            throw new ValidationException("First name is required.");
        }

        if ((lastName == null) || (lastName.trim().length() == 0)) {
            throw new ValidationException("Last name is required.");
        }

        if (region == null) {
            throw new ValidationException("Region is required.");
        }

        if (startDate == null) {
            throw new ValidationException("Start date is required.");
        }

    }

    public Long getId() {
        return id;
    }

    public Integer getVersion() {
        return version;
    }

    public void setVersion(Integer version) {
        this.version = version;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Regions getRegion() {
        return region;
    }

    public void setRegion(Regions region) {
        this.region = region;
    }

    public Date getStartDate() {
        return startDate;
    }

    public void setStartDate(Date startDate) {
        this.startDate = startDate;
    }

}