Query
A Query sorts and filters the data at a Database location so only a subset of the child data is included. This can be used to order a collection of data by some attribute (for example, height of dinosaurs) as well as to restrict a large list of items (for example, chat messages) down to a number suitable for synchronizing to the client. Queries are created by chaining together one or more of the filter methods defined here.
Just as with a Reference, you can receive data from a Query by using the on() method. You will
only receive events and DataSnapshots for the subset of the data that matches your query.
Properties
Methods
endAt
</>Creates a Query with the specified ending point.
endAt(value: number | string | boolean | null, key?: undefined | string): Query;
equalTo
</>Creates a Query with the specified ending point.
equalTo(value: number | string | boolean | null, key?: undefined | string): Query;
isEqual
</>Returns whether or not the current and provided queries represent the same location, have the same query parameters.
isEqual(other: Query): boolean;
keepSynced
</>By calling keepSynced(true) on a location, the data for that location will automatically
be downloaded and kept in sync, even when no listeners are attached for that location.
keepSynced(bool: boolean): Promise<void>;
limitToFirst
</>Generates a new Query limited to the first specific number of children.
limitToFirst(limit: number): Query;
limitToLast
</>Generates a new Query object limited to the last specific number of children.
limitToLast(limit: number): Query;
off
</>Detaches a callback previously attached with on().
off(eventType?: EventType, callback?: undefined | (a: DataSnapshot, b: string | null) => void, context?: Record<string, any>): void;
on
</>Listens for data changes at a particular location.
on(eventType?: EventType, callback?: undefined | (data: DataSnapshot, previousChildKey: undefined | string) => void, cancelCallbackOrContext?: (a: Error) => void | Record<string, any> | null, context?: Record<string, any> | null): (a: DataSnapshot, b: string | null) => void;
once
</>Listens for exactly one event of the specified event type, and then stops listening.
once(eventType: EventType, successCallback?: undefined | (a: DataSnapshot, b: string | null) => any, failureCallbackContext?: (a: Error) => void | Record<string, any> | null): Promise<DataSnapshot>;
orderByChild
</>Generates a new Query object ordered by the specified child key.
orderByChild(path: string): Query;
