ToMany: Set an comparator to define the order of entities

Author: greenrobot

objectbox-java/src/main/java/io/objectbox/relation/ToMany.java

@@ -72,6 +72,7 @@ public class ToMany<TARGET> implements List<TARGET>, Serializable {
  transient private Box entityBox;
  transient private volatile Box<TARGET> targetBox;
  transient private boolean removeFromTargetBox;
+ transient private Comparator<TARGET> comparator;
 
  public ToMany(Object sourceEntity, RelationInfo<TARGET> relationInfo) {
  if(sourceEntity == null ) {
@@ -93,6 +94,12 @@ public void setListFactory(ListFactory listFactory) {
  this.listFactory = listFactory;
  }
 
+ /** Set an comparator to define the order of entities. */
+ @Experimental
+ public void setComparator(Comparator<TARGET> comparator) {
+ this.comparator = comparator;
+ }
+
  /**
  * On put, this also deletes removed entities from the target Box.
  * Note: removed target entities won't cascade the delete.
@@ -162,6 +169,9 @@ private void ensureEntities() {
  newEntities = targetBox.internalGetBacklinkEntities(relationInfo.targetInfo.getEntityId(),
  relationInfo.targetIdProperty, id);
  }
+ if(comparator != null) {
+ Collections.sort(newEntities, comparator);
+ }
  synchronized (this) {
  if (entities == null) {
  entities = newEntities;

tests/objectbox-java-test/src/main/java/io/objectbox/relation/RelationTest.java

@@ -18,6 +18,7 @@
 
 import org.junit.Test;
 
+import java.util.Comparator;
 import java.util.List;
 
 import io.objectbox.query.Query;
@@ -55,6 +56,28 @@ public void testRelationToMany() {
  assertEquals("Oranges", orders.get(1).getText());
  }
 
+ @Test
+ public void testRelationToMany_comparator() {
+ Customer customer = putCustomer();
+ putOrder(customer, "Bananas");
+ putOrder(customer, "Oranges");
+ putOrder(customer, "Apples");
+
+ ToMany<Order> orders = (ToMany<Order>) customer.getOrders();
+ orders.setComparator(new Comparator<Order>() {
+ @Override
+ public int compare(Order o1, Order o2) {
+ return o1.text.compareTo(o2.text);
+ }
+ });
+ orders.reset();
+
+ assertEquals(3, orders.size());
+ assertEquals("Apples", orders.get(0).getText());
+ assertEquals("Bananas", orders.get(1).getText());
+ assertEquals("Oranges", orders.get(2).getText());
+ }
+
  @Test
  public void testRelationToMany_activeRelationshipChanges() {
  Customer customer = putCustomer();