IMPORTANT: In July 2025, we stopped releasing new versions of KTX modules, and we removed the KTX libraries from the Firebase Android BoM (v34.0.0). If you use KTX APIs from the previously released KTX modules, we recommend that you migrate your app to use KTX APIs from the main modules instead. For details, see the FAQ about this initiative.

MutableData

public class MutableData

Instances of this class encapsulate the data and priority at a location. It is used in transactions, and it is intended to be inspected and then updated to the desired data at that location. Note that changes made to a child MutableData instance will be visible to the parent and vice versa.

Summary

Public methods
`@NonNull MutableData`	`child(@NonNull String path)` Used to obtain a MutableData instance that encapsulates the data and priority at the given relative path.
`boolean`	`equals(Object o)`
`@NonNull Iterable<MutableData>`	`getChildren()` Used to iterate over the immediate children at this location
`long`	`getChildrenCount()`
`@Nullable String`	`getKey()`
`@Nullable Object`	`getPriority()` Gets the current priority at this location.
`@Nullable Object`	`getValue()` getValue() returns the data contained in this instance as native types.
`@Nullable T`	`<T> getValue(@NonNull GenericTypeIndicator<T> t)` Due to the way that Java implements generics, it takes an extra step to get back a properly-typed Collection.
`@Nullable T`	`<T> getValue(@NonNull Class<T> valueType)` This method is used to marshall the data contained in this instance into a class of your choosing.
`boolean`	`hasChild(@NonNull String path)`
`boolean`	`hasChildren()`
`void`	`setPriority(@Nullable Object priority)` Sets the priority at this location
`void`	`setValue(@Nullable Object value)` Set the data at this location to the given value.
`String`	`toString()`

Extension functions
`final T`	`<T extends Object> DatabaseKt.getValue(@NonNull MutableData receiver)` Returns the content of the MutableData converted to a POJO.

Public methods

child

public @NonNull MutableData child(@NonNull String path)

Used to obtain a MutableData instance that encapsulates the data and priority at the given relative path.

Parameters
`@NonNull String path`	A relative path

Returns
`@NonNull MutableData`	An instance encapsulating the data and priority at the given path

equals

public boolean equals(Object o)

getChildren

public @NonNull Iterable<MutableData> getChildren()

Used to iterate over the immediate children at this location

    for (MutableData child : parent.getChildren()) {
            ...
    }

Returns
`@NonNull Iterable<MutableData>`	The immediate children at this location

getChildrenCount

public long getChildrenCount()

Returns
`long`	The number of immediate children at this location

getKey

public @Nullable String getKey()

Returns
`@Nullable String`	The key name of this location, or null if it is the top-most location

getPriority

public @Nullable Object getPriority()

Gets the current priority at this location. The possible return types are:

Double
String

Note that null is allowed

Returns
`@Nullable Object`	The priority at this location as a native type or null if no priority was set

getValue

public @Nullable Object getValue()

getValue() returns the data contained in this instance as native types. The possible types returned are:

Boolean
Long
Double
String
Map<String, Object>
List<Object>

This list is recursive; the possible types for java.lang.Object in the above list is given by the same list. These types correspond to the types available in JSON.

Returns
`@Nullable Object`	The data contained in this instance as native types, or null if there is no data at this location.

getValue

public @Nullable T <T> getValue(@NonNull GenericTypeIndicator<T> t)

Due to the way that Java implements generics, it takes an extra step to get back a properly-typed Collection. So, in the case where you want a java.util.List of Message instances, you will need to do something like the following:

    GenericTypeIndicator<List<Message>> t =
        new GenericTypeIndicator<List<Message>>() {};
    List<Message> messages = mutableData.getValue(t);

It is important to use a subclass of GenericTypeIndicator. See GenericTypeIndicator for more details

Parameters
`<T>`	The type to return. Implicitly defined from the `GenericTypeIndicator` passed in
`@NonNull GenericTypeIndicator<T> t`	A subclass of `GenericTypeIndicator` indicating the type of generic collection to be returned.

Returns
`@Nullable T`	A properly typed collection, populated with the data from this instance, or null if there is no data at this location.

getValue

public @Nullable T <T> getValue(@NonNull Class<T> valueType)

This method is used to marshall the data contained in this instance into a class of your choosing. The class must fit 2 simple constraints:

The class must have a default constructor that takes no arguments
The class must define public getters for the properties to be assigned. Properties without a public getter will be set to their default value when an instance is deserialized

An example class might look like:

    class Message {
        private String author;
        private String text;

        private Message() {}

        public Message(String author, String text) {
            this.author = author;
            this.text = text;
        }

        public String getAuthor() {
            return author;
        }

        public String getText() {
            return text;
        }
    }


    // Later
    Message m = mutableData.getValue(Message.class);

Parameters
`<T>`	The type to return. Implicitly defined from the class passed in
`@NonNull Class<T> valueType`	The class into which this data in this instance should be marshalled

Returns
`@Nullable T`	An instance of the class passed in, populated with the data from this instance, or null if there is no data at this location.

hasChild

public boolean hasChild(@NonNull String path)

Parameters
`@NonNull String path`	A relative path

Returns
`boolean`	True if data exists at the given path, otherwise false

hasChildren

public boolean hasChildren()

Returns
`boolean`	True if the data at this location has children, false otherwise

setPriority

public void setPriority(@Nullable Object priority)

Sets the priority at this location

Parameters
`@Nullable Object priority`	The desired priority or null to clear the existing priority

setValue

public void setValue(@Nullable Object value)

Set the data at this location to the given value. The native types accepted by this method for the value correspond to the JSON types:

Boolean
Long
Double
Map<String, Object>
List<Object>

In addition, you can set instances of your own class into this location, provided they satisfy the following constraints:

The class must have a default constructor that takes no arguments
The class must define public getters for the properties to be assigned. Properties without a public getter will be set to their default value when an instance is deserialized

Generic collections of objects that satisfy the above constraints are also permitted, i.e. Map<String, MyPOJO>, as well as null values.

Note that this overrides the priority, which must be set separately.

Parameters
`@Nullable Object value`	The value to set at this location or null to delete the existing data

Throws
`com.google.firebase.database.DatabaseException com.google.firebase.database.DatabaseException`

toString

public String toString()

Extension functions

DatabaseKt.getValue

public final T <T extends Object> DatabaseKt.getValue(@NonNull MutableData receiver)

Returns the content of the MutableData converted to a POJO.

Supports generics like List<> or Map<>. Use @JvmSuppressWildcards to force the compiler to use the type T, and not ? extends T.