Liferay and relationships in it

Question

I have a portlet, which can add/update/delete books and add authors. Moreover, you can choose existing authors when you try to add book.

And now I need to show how many books were written by each author in "author" table. How can I do it? Im a newbie in liferay and I even have no idea.

It's my service.xml

<entity name="Book" local-service="true" remote-service="true"  cache-enabled="false">

    <column name="bookId" type="long" primary="true" />
    <column name="bookName" type="String" />
    <column name="bookDescription" type="String" />
    <column name="authors" type="Collection" entity="Author" mapping-table="Books_Authors" />
    <finder return-type="Collection" name="bookName">
        <finder-column name="bookName"></finder-column>
    </finder>

</entity>

<entity name="Author" local-service="true" remote-service="true" cache-enabled="false">
    <column name="authorId" type="long" primary="true" />
    <column name="authorName" type="String" />
    <column name="books" type="Collection" entity="Book" mapping-table="Books_Authors" />

</entity>

Answer 1

Service Builder is your friend.

You just need to add a finder in your book entity in service.xml. If your entity has a field named author:

<finder name="Author" return-type="Collection">
    <finder-column name="author" />
</finder>

The execution of build-service will generate the methods BookUtil.findByAuthor() and BookUtil.countByAuthor().

You can implement now the corresponding methods in BookLocalServiceImpl, calling the previous, and after another run of build-serivce, they're available in your Util class. Something like

public List<Book> getByAuthor(String author) {
    return getPersistence().findByAuthor(author);
}

public int countByAuthor(String author) {
    return getPersistence().countByAuthor(author);
}

After the last call to build-service you can call them from your BookLocalServiceUtil.

If you just want the count, don't retrieve all the collection. If there are many records, it's a bad idea. Invoke the count instead.