Realm Query Language

Realm Query Language (RQL) is a string-based query language to constrain searches when retrieving objects from a realm. SDK-specific methods pass queries to the Realm query engine, which retrieves matching objects from the realm. Realm Query Language syntax is based on NSPredicate.

Queries evaluate a predicate for every object in the collection being queried. If the predicate resolves to true, the results collection includes the object.

You can use Realm Query Language in most Realm SDKs with your SDK's filter or query methods. The Swift SDK is the exception, as it uses the NSPredicate query API. Some SDKs also support idiomatic APIs for querying realms in their language.

You can also use Realm Query Language to browse for data in Realm Studio. Realm Studio is a visual tool to view, edit, and design Realm files.

Examples on This Page

Many of the examples in this page use a simple data set for a to-do list app. The two Realm object types are Project and Item.

• An Item has a name, assignee's name, and completed flag. There is also an arbitrary number for priority (higher is more important) and a count of minutes spent working on it.
• A Project has zero or more Items and an optional quota for minimum number of to-do items expected to be completed.

See the schema for these two classes, Project and Item, below:

Java

public class Item extends RealmObject {
  ObjectId id = new ObjectId();
  String name;
  Boolean isComplete = false;
  String assignee;
  Integer priority = 0;
  Integer progressMinutes = 0;
  @LinkingObjects("items")
  final RealmResults<Project> projects = null;
}
public class Project extends RealmObject {
  ObjectId id = new ObjectId();
  String name;
  RealmList<Item> items;
  Integer quota = null;
}

Kotlin

open class Item(): RealmObject() {
  var id: ObjectId = new ObjectId()
  @FullText
  lateinit var name: String
  var isComplete: Boolean = false
  var assignee: String? = null
  var priority: Int = 0
  var progressMinutes: Int = 0
}

open class Project(): RealmObject() {
  var id: ObjectId = new ObjectId()
  lateinit var name: String
  lateinit var items: RealmList<Item>
  var quota: Int? = null
}

Expressions

Filters consist of expressions in a predicate. An expression consists of one of the following:

• The name of a property of the object currently being evaluated.
• An operator and up to two argument expression(s). For example, in the expression A + B, the entirety of A + B is an expression, but A and B are also argument expressions to the operator +.
• A value, such as a string ('hello') or a number (5).

"progressMinutes > 1 AND assignee == $0", "Ali"

Parameterized Queries

Create parameterized queries to interpolate variables into prepared Realm Query Language statements. The syntax for interpolated variables is $<int>, starting at 0. Pass the positional arguments as additional arguments to Realm SDK methods that use Realm Query Language.

Include just one parameter with $0.

"progressMinutes > 1 AND assignee == $0", "Ali"

Include multiple parameters with ascending integers starting at $0.

"progressMinutes > $0 AND assignee == $1", 1, "Alex"

Query Formats

The following table shows how a query should be formatted when serialized and parameterized for the following data types:

Dot Notation

When referring to an object property, you can use dot notation to refer to child properties of that object. You can even refer to the properties of embedded objects and relationships with dot notation.

For example, consider a query on an object with a workplace property that refers to a Workplace object. The Workplace object has an embedded object property, address. You can chain dot notations to refer to the zipcode property of that address:

"workplace.address.zipcode == 10019"

Nil Type

Realm Query Language include the nil type to represent a null pointer. You can either reference nil directly in your queries or with a parameterized query. If you're using a parameterized query, each SDK maps its respective null pointer to nil.

"assignee == nil"

// comparison to language null pointer
"assignee == $0", null

Comparison Operators

The most straightforward operation in a search is to compare values.

Important: The type on both sides of the operator must be equivalent. For example, comparing an ObjectId with string will result in a precondition failure with a message like:

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"Expected object of type object id for property 'id' on object of type
'User', but received: 11223344556677889900aabb (Invalid value)"

You can compare any numeric type with any other numeric type, including decimal, float, and Decimal128.

Example: The following example uses Realm Query Language's comparison operators to:

• Find high priority to-do items by comparing the value of the priority property value with a threshold number, above which priority can be considered high.
• Find long-running to-do items by seeing if the progressMinutes property is at or above a certain value.
• Find unassigned to-do items by finding items where the assignee property is equal to null.
• Find to-do items within a certain time range by finding items where the progressMinutes property is between two numbers.
• Find to-do items with a certain amount of progressMinutes from the given list.

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  // Find high priority to-do items by comparing the value of the ``priority``
  // property value with a threshold number, above which priority can be considered high.
  "priority > $0", 5

  // Find long-running to-do items by seeing if the progressMinutes property is at or above a certain value.
  "progressMinutes > $0", 120

  // Find unassigned to-do items by finding items where the assignee property is equal to null.
  "assignee == $0", null

  // Find to-do items within a certain time range by finding items
  // where the progressMinutes property is between two numbers.
  "progressMinutes BETWEEN { $0 , $1 }", 30, 60

  // Find to-do items with a certain amount of progressMinutes from the given list.
  "progressMinutes IN { $0, $1, $2, $3, $4, $5 }", 10, 20, 30, 40, 50, 60

Logical Operators

Make compound predicates using logical operators.

Example: We can use the query language's logical operators to find all of Ali's completed to-do items. That is, we find all items where the assignee property value is equal to 'Ali' AND the isComplete property value is true:

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"assignee == $0 AND isComplete == $1", "Ali", true

String Operators

Compare string values using these string operators. Regex-like wildcards allow more flexibility in search.

Note: You can use the following modifiers with the string operators:

• [c] for case insensitivity. "name CONTAINS[c] $0", 'a'

Example: We use the query engine's string operators to find:

• Projects with a name starting with the letter 'e'
• Projects with names that contain 'ie'

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  "name BEGINSWITH[c] $0", 'e'

  "name CONTAINS $0", 'ie'

ObjectId and UUID Operators

Query BSON ObjectIds and UUIDs. These data types are often used as primary keys.

To query with ObjectIds, use a parameterized query. Pass the ObjectId or UUID you're querying against as the argument.

"_id == $0", oidValue

You can also put a string representation of the ObjectId you're evaluating in oid(<ObjectId String>).

"_id == oid(6001c033600510df3bbfd864)"

To query with UUIDs, put a string representation of the UUID you're evaluating in uuid(<UUID String>).

"id == uuid(d1b186e1-e9e0-4768-a1a7-c492519d47ee)"

Arithmetic Operators

Perform basic arithmetic in one side of a RQL expression when evaluating numeric data types.

  "2 * priority > 6"
  // Is equivalent to
  "priority >= 2 * (2 - 1) + 2"

You can also use multiple object properties together in a mathematic operation.

"progressMinutes * priority == 90"

Type Operator

Check the type of a property using the @type operator. You can only use the type operator with mixed types and dictionaries.

Evaluate the property against a string representation of the data type name. Refer to SDK documentation on the mapping from the SDK language's data types to Realm data types.

  "mixedType.@type == 'string'"

  "mixedType.@type == 'bool'"

Dictionary Operators

Compare dictionary values using these dictionary operators.

You can also use dictionary operators in combination with comparison operators to filter objects based on dictionary keys and values. The following examples show some ways to use dictionary operators with comparison operators. All examples query a collection of Realm objects with a dictionary property named dict.

Example: The following examples use various dictionary operators.

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  // Evaluates if there is a dictionary key with the name 'foo'
  "ANY dict.@keys == $0", 'foo'

  // Evaluates if there is a dictionary key with key 'foo' and value 'bar
  "dict['foo'] == $0", 'bar'

  // Evaluates if there is greater than one key-value pair in the dictionary
  "dict.@count > $0", 1

  // Evaluates if dictionary has property of type 'string'
  "ANY dict.@type == 'string'"

  // Evaluates if all the dictionary's values are integers
  "ALL dict.@type == 'bool'"

  // Evaluates if dictionary does not have any values of type int
  "NONE dict.@type == 'double'"

  // ANY is implied.
  "dict.@type == 'string'"

Date Operators

Query date types in a realm.

Generally, you should use a parameterized query to pass a date data type from the SDK language you are using to a query.

"timeCompleted < $0", someDate

You can also specify dates in the following two ways:

• As a specific date (in UTC)- YYYY-MM-DD@HH:mm:ss:nnnnnnnnnn (year-month-day@hours:minutes:seconds:nanoseconds), UTC. You can also use T instead of @ to separate the date from the time.
• As a time in seconds since the Unix epoch- Ts:n, where T designates the start of the time, s is the number of seconds, and n is the number of nanoseconds.

Date supports comparison operators.

Example: The following example shows how to use a parameterized query with a date object:

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var date = new Date("2021-02-20@17:30:15:0");

  "timeCompleted > $0", date

Aggregate Operators

Apply an aggregate operator to a collection property of a Realm object. Aggregate operators traverse a collection and reduce it to a single value.

Example: These examples all query for projects containing to-do items that meet this criteria:

• Projects with average item priority above 5.
• Projects with an item whose priority is less than 5.
• Projects with an item whose priority is greater than 5.
• Projects with more than 5 items.
• Projects with long-running items.

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var priorityNum = 5;

  "[email protected] > $0", priorityNum

  "[email protected] < $0", priorityNum

  "[email protected] > $0", priorityNum

  "items.@count > $0", 5

  "[email protected] > $0", 100

Collection Operators

A collection operator lets you query list properties within a collection of objects. Collection operators filter a collection by applying a predicate to every element of a given list property of the object. If the predicate returns true, the object is included in the output collection.

Example: This example uses collection operators to find projects that contain to-do items matching certain criteria:

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  // Projects with no complete items.
  "NONE items.isComplete == $0", true

  // Projects that contain a item with priority 10
  "ANY items.priority == $0", 10

  // Projects that only contain completed items
  "ALL items.isComplete == $0", true

  // Projects with at least one item assigned to either Alex or Ali
  "ANY items.assignee IN { $0 , $1 }", "Alex", "Ali"

  // Projects with no items assigned to either Alex or Ali
  "NONE items.assignee IN { $0 , $1 }", "Alex", "Ali"

List Comparisons

You can use comparison operators and collection operators to filter based on lists of data.

You can compare any type of valid list. This includes:

• collections of Realm objects, which let you filter against other data in the realm. "oid(631a072f75120729dc9223d9) IN items.id"
• lists defined directly in the query, which let you filter against static data. You define static lists as a comma-separated list of literal values enclosed in opening ({) and closing (}) braces. "priority IN {0, 1, 2}"
• native list objects passed in a parameterized expression, which let you pass application data directly to your queries. const ids = [ new BSON.ObjectId("631a072f75120729dc9223d9"), new BSON.ObjectId("631a0737c98f89f5b81cd24d"), new BSON.ObjectId("631a073c833a34ade21db2b2"), ]; const parameterizedQuery = realm.objects("Item").filtered("id IN $0", ids);

If you do not define a collection operator, a list expression defaults to the ANY operator.

Example: These two list queries are equivalent:

• age == ANY {18, 21}
• age == {18, 21}

Both of these queries return objects with an age property equal to either 18 or 21. You could also do the opposite by returning objects only if the age is not equal to either 18 or 21:

• age == NONE {18, 21}

The following table includes examples that illustrate how collection operators interact with lists and comparison operators:

Full Text Search

You can use RQL to query on properties that have a full-text search (FTS) annotation. FTS supports boolean match word searches, rather than searches for relevance. For information on enabling FTS on a property, see the FTS documentation for your SDK:

• Flutter SDK
• Kotlin SDK
• .NET SDK
• Node.js SDK
• React Native SDK
• Swift SDK does not yet support Full-Text Search.

To query these properties, use the TEXT predicate in your query.

You can search for entire words or phrases, or limit your results with the following characters:

• Exclude results for a word by placing the - character in front of the word.
• Specify prefixes by placing the * character at the end of a prefix. Suffix searching is not currently supported.

In the following example, we query the Item.name property:

    // Filter for items with 'write' in the name
    "name TEXT $0", "write"

    // Find items with 'write' but not 'tests' using '-'
    "name TEXT $0", "write -tests"

    // Find items starting with 'wri-' using '*'
    "name TEXT $0", "wri*"

Full-Text Search Tokenizer Details

Full-Text Search (FTS) indexes support:

• Tokens are diacritics- and case-insensitive.
• Tokens can only consist of characters from ASCII and the Latin-1 supplement (western languages). All other characters are considered whitespace.
• Words split by a hyphen (-) are split into two tokens. For example, full-text splits into full and text.

Backlink Queries

A backlink is an inverse relationship link that lets you look up objects that reference another object. Backlinks use the to-one and to-many relationships defined in your object schemas but reverse the direction. Every relationship that you define in your schema implicitly has a corresponding backlink.

You can access backlinks in queries using the @links.<ObjectType>.<PropertyName> syntax, where <ObjectType> and <PropertyName> refer to a specific property on an object type that references the queried object type.

// Find items that belong to a project with a quota greater than 10 (@links)
"@links.Project.items.quota > 10"

You can also define a linkingObjects property to explicitly include the backlink in your data model. This lets you reference the backlink through an assigned property name using standard dot notation.

// Find items that belong to a project with a quota greater than 10 (LinkingObjects)
"projects.quota > 10"

The result of a backlink is treated like a collection and supports collection operators.

  // Find items where any project that references the item has a quota greater than 0
  "ANY @links.Project.items.quota > 0"
  // Find items where all projects that reference the item have a quota greater than 0
  "ALL @links.Project.items.quota > 0"

You can use aggregate operators on the backlink collection.

  // Find items that are referenced by multiple projects
  "projects.@count > 1"
  // Find items that are not referenced by any project
  "@links.Project.items.@count == 0"
  // Find items that belong to a project where the average item has
  // been worked on for at least 5 minutes
  "@[email protected] > 10"

You can query the count of all relationships that point to an object by using the @count operator directly on @links.

// Find items that are not referenced by another object of any type
"@links.@count == 0"

Subqueries

Iterate through list properties with another query using the SUBQUERY() predicate function.

Subqueries are useful for the following scenarios:

• Matching each object in a list property on multiple conditions
• Counting the number of objects that match a subquery

SUBQUERY() has the following structure:

SUBQUERY(<collection>, <variableName>, <predicate>)

• collection: The name of the property to iterate through
• variableName: A variable name of the element to use in the subquery
• predicate: The subquery predicate. Use the variable specified by variableName to refer to the currently-iterated element.

A subquery iterates through the given collection and checks the given predicate against each object in the collection. The predicate can refer to the current iterated object with the variable name passed to SUBQUERY().

A subquery expression resolves to a list of objects. Realm only supports the @count aggregate operator on the result of a subquery. This allows you to count how many objects in the subquery input collection matched the predicate.

You can use the count of the subquery result as you would any other number in a valid expression. In particular, you can compare the count with the number 0 to return all matching objects.

Example: The following example shows two subquery filters on a collection of projects.

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  // Returns projects with items that have not been completed
  // by a user named Alex.
  "SUBQUERY(items, $item, $item.isComplete == false AND $item.assignee == 'Alex').@count > 0"

  // Returns the projects where the number of completed items is
  // greater than or equal to the value of a project's `quota` property.
  "SUBQUERY(items, $item, $item.isComplete == true).@count >= quota"

Sort, Distinct & Limit

Sort and limit the results collection of your query using additional operators.

Example: Use the query engine's sort, distinct, and limit operators to find to-do items where the assignee is Ali:

• Sorted by priority in descending order
• Enforcing uniqueness by name
• Limiting the results to 5 items

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"assignee == 'Ali' SORT(priority DESC) DISTINCT(name) LIMIT(5)"