Paths

Kotlin JDSL has the Path interface to represent a path expression in JPQL. Use path() and invoke() to build Path.

// Book.isbn.value
path(Book::isbn).path(Isbn::value)
path(Book::isbn)(Isbn::value)

// b.isbn.value
entity(Book::class, "b").path(Book::isbn).path(Isbn::value)
entity(Book::class, "b")(Book::isbn)(Isbn::value)

Java entity

path() and invoke() can take KProperty1 or KFuction1 as an argument. KFunction1 is useful when you use Java entity with private property and public getter.

@Entity
public class Book {
    @Id
    private Long id;

    private String title;

    public String getTitle() {
        return title;
    }
}

// compile error
path(Book::title)

// Book.title
path(Book::getTitle)

Kotlin JDSL infers the property name from the getter with the following rules:

• If the name starts with is, use the name as it is.

• If the name starts with get, remove get and change the first letter to lowercase.

• Otherwise, use the name as it is.

// Book.isAvailable
path(Book::isAvailable)

// Book.available
path(Book::getAvailable)

If you want to use your own rule, implement JpqlPropertyIntrospector and provide it to RenderContext. See Custom DSL for more details. If you are using Spring, see Spring supports also.

class MyIntrospector : JpqlPropertyIntrospector() {
    override fun introspect(property: KCallable<*>): JpqlPropertyDescription? {
        if (property is KFunction1<*, *>) {
            val name = // resolve a name with your own rule
            return MyProperty(name)
        }

        return null
    }

    private data class MyProperty(
        override val name: String,
    ) : JpqlPropertyDescription
}

val myModule = object : JpqlRenderModule {
    override fun setupModule(context: JpqlRenderModule.SetupContext) {
        context.prependIntrospector(MyIntrospector())
    }
}

val myContext = JpqlRenderContext().registerModule(myModule)

Expression

Path can be used as Expression in a select clause or predicate.

// SELECT Book.isbn FROM Book AS Book WHERE Book.isbn.value = :param1
jpql {
    select(
        path(Book::isbn),
    ).from(
        entity(Book::class),
    ).where(
        path(Book::isbn)(Ibsn::value).eq("01"),
    )
}

Treat

Use treat() to typecast Path to subclass.

path(EmployeeDepartment::employee).treat(FullTimeEmployee::class)