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io.realm

Interface OrderedRealmCollection

On this page

  • io.realm
  • Method Summary
  • Inherited Methods
  • Method Detail
  • createSnapshot
  • deleteFirstFromRealm
  • deleteFromRealm
  • deleteLastFromRealm
  • first
  • last
  • sort

io.realm

Implemented interfaces:

  • java.util.List

  • io.realm.RealmCollection

  • java.util.Collection

  • java.lang.Iterable

  • java.util.Collection

  • java.lang.Iterable

An OrderedRealmCollection is a collection which maintains an ordering for its elements. Every element in the OrderedRealmCollection has an index. Each element can thus be accessed by its index, with the first index being zero. Normally, OrderedRealmCollection s allow duplicate elements, as compared to Sets, where elements have to be unique.

There are three types of OrderedRealmCollection . RealmResults and RealmList are live collections. They are up-to-date all the time and they will never contain an invalid RealmObject . OrderedRealmCollectionSnapshot is different. An OrderedRealmCollectionSnapshot can be created from another OrderedRealmCollection . Its size and elements order stay the same as the original collection's when it was created. OrderedRealmCollectionSnapshot may contain invalid RealmObject s if the objects get deleted.

Using iterators to iterate on OrderedRealmCollection will always work. You can delete or modify the elements without impacting the iterator. See below example:

RealmResults<Dog> dogs = realm.where(Dog.class).findAll();
int s = dogs.size(); // 10
realm.beginTransaction();
for (Dog dog : dogs) {
    dog.deleteFromRealm();
    s = dogs.size(); // This will be decreased by 1 every time after a dog is removed.
}
realm.commitTransaction();
s = dogs.size(); // 0

An iterator created from a live collection will create a stable view when the iterator is created, allowing you to delete and modify elements while iterating without impacting the iterator. However, the RealmResults backing the iterator will still be live updated meaning that size and order of elements can change when iterating. RealmList has the same behaviour as RealmResults since they are both live collections.

A simple for-loop is different. See below example:

RealmResults<Dog> dogs = realm.where(Dog.class).findAll();
realm.beginTransaction();
for (int i = 0; i < dogs.size(); i++) {
    dogs.get(i).deleteFromRealm();
}
realm.commitTransaction();
s = dogs.size(); // 5

The above example only deletes half of elements in the RealmResults . This is because of dogs.size() decreased by 1 for every loop. The deletion happens in the loop will immediately impact the size of RealmResults . To solve this problem, you can create a OrderedRealmCollectionSnapshot from the RealmResults or RealmList and do simple for-loop on that instead:

RealmResults<Dog> dogs = realm.where(Dog.class).findAll();
OrderedRealmCollectionSnapshot snapshot = dogs.createSnapshot();
// dogs.size() == 10 && snapshot.size() == 10
realm.beginTransaction();
for (int i = 0; i < snapshot.size(); i++) {
    snapshot.get(0).deleteFromRealm();
    // snapshot.get(0).isValid() == false
}
realm.commitTransaction();
// dogs.size() == 0 && snapshot.size() == 10

As you can see, after deletion, the size and elements order of snapshot stay the same as before. But the element at the position becomes invalid.

Method Summary

Modifier and Type
Method and Description
createSnapshot ()

Creates a snapshot from this OrderedRealmCollection .

public boolean
deleteFirstFromRealm ()

Deletes the first object from the Realm.

public void
deleteFromRealm (
int location
)

Deletes the object at the given index from the Realm.

public boolean
deleteLastFromRealm ()

Deletes the last object from the Realm.

public E
first (
E defaultValue
)

Gets the first object from the collection.

public E
first ()

Gets the first object from the collection.

public E
last (
E defaultValue
)

Gets the last object from the collection.

public E
last ()

Gets the last object from the collection.

sort (
java.lang.String[] fieldNames,
io.realm.Sort[] sortOrders
)

Sorts a collection based on the provided fields and sort orders.

sort (
String fieldName1,
Sort sortOrder1,
String fieldName2,
Sort sortOrder2
)

Sorts a collection based on the provided fields and sort orders.

sort (
String fieldName,
Sort sortOrder
)

Sorts a collection based on the provided field and sort order.

sort (
String fieldName
)

Sorts a collection based on the provided field in ascending order.

Inherited Methods

Method Detail

createSnapshot

Creates a snapshot from this OrderedRealmCollection .

Returns

the snapshot of this collection.

Throws

Tip

See also:

deleteFirstFromRealm

public boolean deleteFirstFromRealm ()

Deletes the first object from the Realm. This also removes it from this collection.

Returns

true if an object was deleted, false otherwise.

Throws

deleteFromRealm

public void deleteFromRealm (
int location
)

Deletes the object at the given index from the Realm. This also removes it from the collection.

Parameters

  • location - the array index identifying the object to be removed.

Throws

deleteLastFromRealm

public boolean deleteLastFromRealm ()

Deletes the last object from the Realm. This also removes it from this collection.

Returns

true if an object was deleted, false otherwise.

Throws

first

public E first (
E defaultValue
)

Gets the first object from the collection. If the collection is empty, the provided default will be used instead.

Returns

the first object or the provided default.

public E first ()

Gets the first object from the collection.

Returns

the first object.

Throws

last

public E last (
E defaultValue
)

Gets the last object from the collection. If the collection is empty, the provided default will be used instead.

Returns

the last object or the provided default.

public E last ()

Gets the last object from the collection.

Returns

the last object.

Throws

sort

public RealmResults sort (
java.lang.String[] fieldNames,
io.realm.Sort[] sortOrders
)

Sorts a collection based on the provided fields and sort orders.

Parameters

  • fieldNames - an array of field names to sort by. Only fields of type boolean, short, int, long, float, double, Date, and String are supported.

  • sortOrders - the directions to sort by.

Returns

a new sorted RealmResults will be created and returned. The original collection stays unchanged.

Throws

public RealmResults sort (
String fieldName1,
Sort sortOrder1,
String fieldName2,
Sort sortOrder2
)

Sorts a collection based on the provided fields and sort orders.

Parameters

  • fieldName1 - first field name. Only fields of type boolean, short, int, long, float, double, Date, and String are supported.

  • sortOrder1 - sort order for first field.

  • fieldName2 - second field name. Only fields of type boolean, short, int, long, float, double, Date, and String are supported.

  • sortOrder2 - sort order for second field.

Returns

a new sorted RealmResults will be created and returned. The original collection stays unchanged.

Throws

public RealmResults sort (
String fieldName,
Sort sortOrder
)

Sorts a collection based on the provided field and sort order.

Parameters

  • fieldName - the field name to sort by. Only fields of type boolean, short, int, long, float, double, Date, and String are supported.

  • sortOrder - the direction to sort by.

Returns

a new sorted RealmResults will be created and returned. The original collection stays unchanged.

Throws

public RealmResults sort (
String fieldName
)

Sorts a collection based on the provided field in ascending order.

Parameters

  • fieldName - the field name to sort by. Only fields of type boolean, short, int, long, float, double, Date, and String are supported.

Returns

a new sorted RealmResults will be created and returned. The original collection stays unchanged.

Throws

Back

OrderedCollectionChangeSet.State

Next

OrderedRealmCollectionChangeListener