Using "related" fields/properties in vaadin tables with JPA containers

Vaadin is a Java framework for building modern web applications that look great, perform well and make you and your users happy.

It has a lot of features which help you in building data driven applications, without having to code everything yourself.
As with any powerfull frameworks you often come to a plcae where a "simple" thing isn't that simple to implement.
Perhaps the framework is just not prepared for that simple feature you wish to use, or you don't find the way to use it correctly.

Vaadin has containers which allow you do present data in forms and tables, without needing to code everything yourself.
There exist different types of containers, depending on your original data source, for example you can have SQL database, Bean objects and many others as a source.

With the JPA container, you can use to handle then whole data stuff with JPA.
So you could for example use hibernate or eclispelink to back your java objects in a sql database.

There is a whole chapter in the book of vaadin describing the JPA container.
When you have a object which has relations to other objects, then you can also specify the JPA container about such "related" properties or fields.
For example when you have a Person object, which has a relation to a country object, you can teel the JPA container about the additional fields available from the Country object.

// Have a persistent container
JPAContainer<Person> persons =
    JPAContainerFactory.make(Person.class, "book-examples");

// Add a nested property to a many-to-one property
persons.addNestedContainerProperty("country.name");
        
// Show the persons in a table, except the "country" column,
// which is an object - show the nested property instead
Table personTable = new Table("The Persistent People", persons);
personTable.setVisibleColumns(new String[]{"name","age",
                                           "country.name"});


// Have a nicer caption for the country.name column
personTable.setColumnHeader("country.name", "Nationality");

The Vaadin JPA container automagically knows to go via the object/database relation and retrieve the correct values.

When you use the filtering table add on available from the vaadin add ons, you can also implement filters on these additional fields.

For this you have to implement the FilterGenerator interface and then tell the table which properties are handled with this filter.

Of course your filter code must then generate the correct filter criterias.

@Override
public Container.Filter generateFilter(Object propertyId, Object value)
{
    if ("country.name".equals(propertyId))
    {
        if (value != null && value instanceof String)
        {
            return new Like("name", value.toString()+"%");
        }
    }
}

Vaadin JPAContainer, Filterable table and related entities

In the web 2.0 framework Vaadin you have containers which provide data to be displayed in your application.
These containers are very flexible and can for example be a databasebackend, a JPA system or your own implementation.

In my past post I showed you how to implement filtering for related fields.

Vaadin also provides many data aware components, for example a table component.
The table component is very sophisticated and allows displaying huge amounts of data in the webbrowser. The table has a lazy loading system, so as only the visible parts of a table are retrieved from the backend and sent to the webbrowser.

There also exists a addon component which has built in filter and sort support.

When using the table with jpa container, then you have to use several tricks to allow filtering on related fields.

The first trick is to display the related fields in the table

For this the simplest way is to add these related fields to the main entity you display.
You don't have to store the property, it's enough for the JPA container when you have a getXXX() method.

That way it displays the additional properties in the table. You could also use this way to show calculated related fields in the table.

This could look like this:
public String getProjectInfos()
{
    return projectNr+" - "+name;
}

When you now display these in the table, you can also filter on that field.
But then, you will get a error message, telling you that the sql select did not find the field for the where condition.

For this to work, you have to use the second trick

You can build your own FilterGenerator which then builds the correct criterias for your tables and relations.

contentTable.setFilterGenerator(new MyFilterGenerator());

The filter generator has different methods, when you don't want to override them, you can just return NULL and then the default behaviour is done.

For us the interesting method is the generateFilter() method.
Here you can implement your own conditions.

If you for example wish to filter with the LIKE statement, then you can do it this way:

@Override
public Container.Filter generateFilter(Object propertyId, Object value)
{
    if ("contract".equals(propertyId))
    {
        if (value != null && value instanceof String)
        {
            return new Like("contractID", value.toString()+"%");
        }
    }
    return null;
}

To now filter on a related table, you can use the IN condition, which then builds the correct sql statements.

@Override
public Container.Filter generateFilter(Object propertyId, Object value)
{
       if ("contracts".equals(propertyId))
        {
            if (value != null && value instanceof String)
            {
                String  lsNr= (String) value;
                EntityManager em= ((MyVaadinUI)UI.getCurrent()).getEntityManager();
                TypedQuery<Shippings> tq= em.createNamedQuery("Shippings.findByLikeProjectNr", Shippings.class);
                tq.setParameter("projectNr", lsNr+"%");
                List<Shippings> rs= tq.getResultList();
                if (rs.isEmpty())
                {
                    return new IsNull("shipping");
                }
                else
                {
                    if (rs.size() > 2000)
                    {
                        Notification.show("To many entries", "\n\nMake more restrictions", Notification.Type.WARNING_MESSAGE);
                        return new IsNull("shipping");
                    }
                    else
                    {
                        return new In("shipping", rs);
                    }
                }
            }
        }
    return null;
}

So when the property contracts has some value, we filter the contracts by projectNr and use the resulting result set to specify as the IN criteria.

If you are still with me, then you probably have a compiler error when you try this code.
The reason is, that the default JPAContainer has no implementation of the IN criteria.
Unfortunally the design of the JPAContainer does not allow to expand the capabilities in that area.

Fortunally there exists a fork of the JPAContainer which just provides the required IN() clause.
You can download the sources and add them to your project.

The source can be found here: https://github.com/lelmarir/jpacontainer

You can learn how to show related / nested properties in this post.