Docs Menu
Docs Home
/ /
Atlas Device SDKs
/ / /

Results Collections - .NET SDK

On this page

  • Results Collections
  • Results are Lazily Evaluated
  • Working wth Collections
  • Collections are Live
  • Limiting Query Results
  • Pagination

A Realm results collection represents the lazily-evaluated results of a query operation. As such, a results collection contains zero or more instances of a single Realm type.

Important

Results are immutable: you cannot add or remove elements on the results collection. This is because the contents of a results collection are determined by a query against the database.

You can filter and sort any collection using Realm's query engine. Collections are live, so they always reflect the current state of the realm instance on the current thread. You can also listen for changes in the collection by subscribing to collection notifications.

Realm only runs a query when you actually request the results of that query, e.g. by accessing elements of the results collection. This lazy evaluation enables you to write elegant, highly performant code for handling large data sets and complex queries.

Like live objects, Realm collections are usually live:

  • Live results collections always reflect the current results of the associated query.

  • Live lists always reflect the current state of the relationship on the realm instance.

There are two cases, however, when a collection is not live:

  • The collection is unmanaged. For example, a collection property of a Realm object that has not been added to a realm yet, or that has been copied from a realm.

  • The collection is frozen.

Combined with collection notifications, live collections enable clean, reactive code. For example, suppose your view displays the results of a query. You can keep a reference to the results collection in your view class, then read the results collection as needed without having to refresh it or validate that it is up-to-date.

Important

Indexes may change

Since results update themselves automatically, do not store the positional index of an object in the collection or the count of objects in a collection. The stored index or count value could be outdated by the time you use it.

The following example shows how to query a results collection in several ways:

var plants = realm.All<Plant>();
// Use the Where operator to find items
// in the results collection
var pricklyPear = plants
.Where(plant => plant.Name == "Prickly Pear");
// Or apply a filter to the results collection
var pricklyPears = plants
.Filter("Name == 'Prickly Pear'");
// You can query collection properties in the same way
var morePlants = realm.All<Inventory>().ElementAt(0).Plants;
// Convert the Ilist<Plant> to an IQueryable and
// use the Where operator
var pricklyPearCacti = morePlants.AsQueryable()
.Where(plant => plant.Name == "Prickly Pear");
// Or apply a filter to the collection
var greenPlants = realm.All<Inventory>()
.Filter("Plants.Color CONTAINS[c] 'Green'");

As a result of lazy evaluation, you do not need any special mechanism to limit query results with Realm. For example, if your query matches thousands of objects, but you only want to load the first ten, simply access only the first ten elements of the results collection.

Thanks to lazy evaluation, the common task of pagination becomes quite simple. For example, suppose you have a results collection associated with a query that matches thousands of objects in your realm. You display one hundred objects per page. To advance to any page, simply access the elements of the results collection starting at the index that corresponds to the target page.

← Field Types - .NET SDK