Package org.javers.core.diff.custom

Interface CustomPropertyComparator<T,C extends PropertyChange>

Type Parameters:

T - Custom Type

C - Concrete type of PropertyChange returned by a comparator

All Superinterfaces:

CustomValueComparator<T>

public interface CustomPropertyComparator<T,C extends PropertyChange>
extends CustomValueComparator<T>

Property-scope comparator bounded to CustomType.

Custom Types are not easy to manage, use it as a last resort,
only for corner cases like comparing custom Collection types.

Typically, Custom Types are large structures (like Multimap).
Implementation should calculate diff between two objects of given Custom Type.

Usage:

 JaversBuilder.javers()
              .registerCustomType( Multimap.class, new GuavaCustomComparator())
              .build()
 

See Also:

https://javers.org/documentation/diff-configuration/#custom-comparators, CustomValueComparator

Method Summary

Modifier and Type	Method	Description
java.util.Optional<C>	compare(T left, T right, PropertyChangeMetadata metadata, Property property)	Called by JaVers to calculate property-to-property diff between two Custom Type objects.
default java.lang.String	toString(T value)	This method has two roles.

Methods inherited from interface org.javers.core.diff.custom.CustomValueComparator

equals

Method Detail

compare

java.util.Optional<C> compare(T left,
                              T right,
                              PropertyChangeMetadata metadata,
                              Property property)

Called by JaVers to calculate property-to-property diff between two Custom Type objects. Can calculate any of concrete PropertyChange.

Implementation of compare() should be consistent with CustomValueComparator.equals(Object, Object). When compare() returns Optional.empty(), equals() should return false.

Parameters:

left - left (or old) value

right - right (or current) value

metadata - call PropertyChangeMetadata.getAffectedCdoId() to get Id of domain object being compared

property - property being compared

Returns:

should return Optional.empty() if compared objects are the same

toString

default java.lang.String toString(T value)

Description copied from interface: CustomValueComparator

This method has two roles. First, it is used when Values are compared in hashing contexts. Second, it is used to build Entity Ids from Values.

Hashcode role

When a Value class has custom toString(), it is used instead of Object.hashCode() when comparing Values in hashing contexts, so:

• Sets with Values
• Lists with Values compared as ListCompareAlgorithm.AS_SET
• Maps with Values as keys

Custom toString() implementation should be aligned with custom CustomValueComparator.equals(Object, Object) in the same way like Object.hashCode() should be aligned with Object.equals(Object).

Entity Id role

Each Value can serve as an Entity Id.
When a Value has custom toString() function, it is used for creating InstanceId for Entities. If a Value doesn't have a custom toString() , default ReflectionUtil.reflectiveToString(Object)) is used.

See full example CustomToStringExample.groovy.

Specified by:

toString in interface CustomValueComparator<T>

Parameters:

value - not null