Client and backend. This class is shared: the same code is compiled into your app and into your server, so everything on this page works in both.
public final class Ref<T>
- Object
- Ref
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.
Methods
public static <T> Ref<T> of(T target) | A ref to target, or an empty one when target is null. |
public static <T> Ref<T> empty() | A ref to nothing. |
public T get() | The target, read through the owning session if it has not been read yet; null when the ref is empty. |
public boolean isPresent() | True when the ref points at an entity, read or not. |
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. |
public boolean isLoaded() | True once the target has been read, or for a ref that was built with a value. |
public boolean equals(Object other) | Indicates whether some other object is “equal to” this one. |
public int hashCode() | Returns a hash code value for the object. |
public String toString() | Returns a string representation of the object. |
protected final void load() | Reads the value through the owning session if it has not been read. |
protected final Object current() | The value as it stands, without reading it. |
protected final void assign(Object target) | Sets a value that needs no reading. |
protected final boolean loaded() | |
protected final Object identifier() | The identifier of the target, read or not, or null without one. |
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. |
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. |
Inherited methods
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)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).
hashCode
public int hashCode()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.)
toString
public String toString()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())
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.