Class Ref<T>

java.lang.Object
com.codename1.orm.Ref<T>
public final class Ref<T> extends Object

A to-one relationship of a record entity, read on first use.

A record cannot be changed after it is built, so it cannot hold a lazy relationship the way an enhanced class does. It holds a Ref instead:

import com.codename1.annotations.Entity;
import com.codename1.annotations.Id;
import com.codename1.annotations.db.ManyToOne;
import com.codename1.orm.Ref;

@Entity
record Customer(@Id long id, String name) {}

@Entity
record Order(@Id long id, @ManyToOne Ref<Customer> customer) {}

Order order = new Order(1, Ref.of(new Customer(7, "Ada")));
String name = order.customer().get().name();

An order the session reads holds an unread Ref: order.customer().id() answers the stored key without a query, and get() reads the customer the first time it's called.

A Ref loaded by a session reads its target through that session, and only while it is open: get() on a Ref that was never read, once the session is closed, throws LazyInitializationException. id() and isPresent() read nothing either, with one exception: on the inverse side of a one-to-one, @OneToOne(mappedBy = ...), the record's own row stores no key, so they read the target, and throw the same way once the session is gone.

To point a record at another entity, build it with Ref.of(target), or Ref.empty() for none. Two refs are equal when they point at the same entity: the same target type and the same identifier.

  • Method Summary

    Modifier and Type
    Method
    Description
    protected final void
    assign(Object target)
    Sets a value that needs no reading.
    protected final Object
    current()
    The value as it stands, without reading it.
    static <T> Ref<T>
    empty()
    A ref to nothing.
    boolean
    equals(Object other)
    Indicates whether some other object is "equal to" this one.
    T
    get()
    The target, read through the owning session if it has not been read yet; null when the ref is empty.
    int
    hashCode()
    Returns a hash code value for the object.
    Object
    id()
    The target's identifier, without reading it unless the ref is the inverse side of a one-to-one; null for an empty ref, or a target that has not been saved yet.
    protected final Object
    identifier()
    The identifier of the target, read or not, or null without one.
    boolean
    isLoaded()
    True once the target has been read, or for a ref that was built with a value.
    boolean
    isPresent()
    True when the ref points at an entity, read or not.
    protected final void
    load()
    Reads the value through the owning session if it has not been read.
    protected final boolean
    loaded()
     
    static <T> Ref<T>
    of(T target)
    A ref to target, or an empty one when target is null.
    protected final Object
    storedIdentifier()
    The identifier as far as it is known, without reading anything.
    protected final Class
    targetType()
    The target's type: the bound relationship's, or the value's own.
    String
    toString()
    Returns a string representation of the object.
    protected final boolean
    unreadable()
    True for the inverse side of a to-one that was never read and can no longer be: its identifier is unknown for good.

    Methods inherited from class Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

  • Method Details

    • of

      public static <T> Ref<T> of(T target)
      A ref to target, or an empty one when target is null.

    • empty

      public static <T> Ref<T> empty()
      A ref to nothing.

    • get

      public T get()

      The target, read through the owning session if it has not been read yet; null when the ref is empty.

      Throws
      • com.codename1.orm.session.LazyInitializationException: if the target was never read and the session that loaded the ref is closed

    • isPresent

      public boolean isPresent()
      True when the ref points at an entity, read or not.

    • id

      public Object id()
      The target's identifier, without reading it unless the ref is the inverse side of a one-to-one; null for an empty ref, or a target that has not been saved yet.

    • isLoaded

      public boolean isLoaded()
      True once the target has been read, or for a ref that was built with a value.

    • equals

      public boolean equals(Object other)
      Description copied from class: Object
      Indicates whether some other object is "equal to" this one. The equals method implements an equivalence relation: It is reflexive: for any reference value x, x.equals(x) should return true. It is symmetric: for any reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true. It is transitive: for any reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true. It is consistent: for any reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the object is modified. For any non-null reference value x, x.equals(null) should return false. The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any reference values x and y, this method returns true if and only if x and y refer to the same object (x==y has the value true).
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Description copied from class: Object
      Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable. The general contract of hashCode is: Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables. As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Description copied from class: Object
      Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method. The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: getClass().getName() + '@' + Integer.toHexString(hashCode())
      Overrides:
      toString in class Object

    • load

      protected final void load()
      Reads the value through the owning session if it has not been read.

    • current

      protected final Object current()
      The value as it stands, without reading it.

    • assign

      protected final void assign(Object target)
      Sets a value that needs no reading.

    • loaded

      protected final boolean loaded()

    • identifier

      protected final Object identifier()
      The identifier of the target, read or not, or null without one. The inverse side of a to-one stores no key, so it reads the target first.

    • unreadable

      protected final boolean unreadable()
      True for the inverse side of a to-one that was never read and can no longer be: its identifier is unknown for good.

    • storedIdentifier

      protected final Object storedIdentifier()
      The identifier as far as it is known, without reading anything.

    • targetType

      protected final Class targetType()
      The target's type: the bound relationship's, or the value's own.