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FirebaseDatabase Framework Reference

FIRDatabaseQuery


@interface FIRDatabaseQuery : NSObject

A DatabaseQuery instance represents a query over the data at a particular location.

You create one by calling one of the query methods (queryOrdered(byChild:), queryStarting(atValue:), etc.) on a DatabaseReference. The query methods can be chained to further specify the data you are interested in observing.

Attach observers to read data

  • This method is used to listen for data changes at a particular location. This is the primary way to read data from the Firebase Database. Your block will be triggered for the initial data and again whenever the data changes.

    Use removeObserverWithHandle: to stop receiving updates.

    Declaration

    Objective-C

    - (FIRDatabaseHandle)
    observeEventType:(FIRDataEventType)eventType
           withBlock:(nonnull void (^)(FIRDataSnapshot *_Nonnull))block;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called with initial data and updates. It is passed the data as a DataSnapshot.

    Return Value

    A handle used to unregister this block later using removeObserver(withHandle:)

  • This method is used to listen for data changes at a particular location. This is the primary way to read data from the Firebase Database. Your block will be triggered for the initial data and again whenever the data changes. In addition, for DataEventTypeChildAdded, DataEventTypeChildMoved, and DataEventTypeChildChanged events, your block will be passed the key of the previous node by priority order.

    Use removeObserver(withHandle:) to stop receiving updates.

    Declaration

    Objective-C

    - (FIRDatabaseHandle)observeEventType:(FIRDataEventType)eventType
       andPreviousSiblingKeyWithBlock:
           (nonnull void (^)(FIRDataSnapshot *_Nonnull,
                             NSString *_Nullable))block;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called with initial data and updates. It is passed the data as a DataSnapshot and the previous child’s key.

    Return Value

    A handle used to unregister this block later using removeObserver(withHandle:)

  • This method is used to listen for data changes at a particular location. This is the primary way to read data from the Firebase Database. Your block will be triggered for the initial data and again whenever the data changes.

    The cancelBlock will be called if you will no longer receive new events due to no longer having permission.

    Use removeObserver(withHandle:) to stop receiving updates.

    Declaration

    Objective-C

    - (FIRDatabaseHandle)
    observeEventType:(FIRDataEventType)eventType
           withBlock:(nonnull void (^)(FIRDataSnapshot *_Nonnull))block
     withCancelBlock:(nullable void (^)(NSError *_Nonnull))cancelBlock;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called with initial data and updates. It is passed the data as a DataSnapshot.
    cancelBlock

    The block that should be called if this client no longer has permission to receive these events

    Return Value

    A handle used to unregister this block later using removeObserver(withHandle:)

  • This method is used to listen for data changes at a particular location. This is the primary way to read data from the Firebase Database. Your block will be triggered for the initial data and again whenever the data changes. In addition, for FIRDataEventTypeChildAdded, FIRDataEventTypeChildMoved, and FIRDataEventTypeChildChanged events, your block will be passed the key of the previous node by priority order.

    The cancelBlock will be called if you will no longer receive new events due to no longer having permission.

    Use removeObserver(withHandle:) to stop receiving updates.

    Declaration

    Objective-C

    - (FIRDatabaseHandle)observeEventType:(FIRDataEventType)eventType
       andPreviousSiblingKeyWithBlock:
           (nonnull void (^)(FIRDataSnapshot *_Nonnull,
                             NSString *_Nullable))block
                      withCancelBlock:
                          (nullable void (^)(NSError *_Nonnull))cancelBlock;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called with initial data and updates. It is passed the data as a DataSnapshot and the previous child’s key.
    cancelBlock

    The block that should be called if this client no longer has permission to receive these events

    Return Value

    A handle used to unregister this block later using removeObserver(withHandle:)

  • This method is used to get the most up-to-date value for this query. This method updates the cache and raises events if successful. If not connected, it returns a locally-cached value.

    Declaration

    Objective-C

    - (void)getDataWithCompletionBlock:
    (void (^_Nonnull)(NSError *_Nullable, FIRDataSnapshot *_Nullable))block;

    Parameters

    block

    The block that should be called with the most up-to-date value of this query, or an error if no such value could be retrieved.

  • This is equivalent to observe(_:with:), except the block is immediately canceled after the initial data is returned.

    Declaration

    Objective-C

    - (void)observeSingleEventOfType:(FIRDataEventType)eventType
                       withBlock:
                           (nonnull void (^)(FIRDataSnapshot *_Nonnull))block;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called. It is passed the data as a DataSnapshot.

  • This is equivalent to observe(_:with:), except the block is immediately canceled after the initial data is returned. In addition, for DataEventTypeChildAdded, DataEventTypeChildMoved, and DataEventTypeChildChanged events, your block will be passed the key of the previous node by priority order.

    Declaration

    Objective-C

    - (void)observeSingleEventOfType:(FIRDataEventType)eventType
    andPreviousSiblingKeyWithBlock:
        (nonnull void (^)(FIRDataSnapshot *_Nonnull, NSString *_Nullable))block;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called. It is passed the data as a DataSnapshot and the previous child’s key.

  • This is equivalent to observe(_:with:), except the block is immediately canceled after the initial data is returned.

    The cancelBlock will be called if you do not have permission to read data at this location.

    Declaration

    Objective-C

    - (void)
    observeSingleEventOfType:(FIRDataEventType)eventType
                   withBlock:(nonnull void (^)(FIRDataSnapshot *_Nonnull))block
             withCancelBlock:(nullable void (^)(NSError *_Nonnull))cancelBlock;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called. It is passed the data as a DataSnapshot.
    cancelBlock

    The block that will be called if you don’t have permission to access this data

  • This is equivalent to observe(_:with:), except the block is immediately canceled after the initial data is returned. In addition, for DataEventTypeChildAdded, DataEventTypeChildMoved, and DataEventTypeChildChanged events, your block will be passed the key of the previous node by priority order.

    The cancelBlock will be called if you do not have permission to read data at this location.

    Declaration

    Objective-C

    - (void)observeSingleEventOfType:(FIRDataEventType)eventType
    andPreviousSiblingKeyWithBlock:(nonnull void (^)(FIRDataSnapshot *_Nonnull,
                                                     NSString *_Nullable))block
                   withCancelBlock:
                       (nullable void (^)(NSError *_Nonnull))cancelBlock;

    Parameters

    eventType

    The type of event to listen for.
    block

    The block that should be called. It is passed the data as a DataSnapshot and the previous child’s key.
    cancelBlock

    The block that will be called if you don’t have permission to access this data

Detaching observers

  • Detach a block previously attached with observe(_:with:), or another query observation method. After this method is called, the associated block registered to receive snapshot updates will no longer be invoked.

    Declaration

    Objective-C

    - (void)removeObserverWithHandle:(FIRDatabaseHandle)handle;

    Parameters

    handle

    The handle returned by the call to observe(_:with:) which we are trying to remove.

  • Detach all blocks previously attached to this Firebase Database location with observe(_:with:) and other query observation methods.

    Declaration

    Objective-C

    - (void)removeAllObservers;

  • 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. Additionally, while a location is kept synced, it will not be evicted from the persistent disk cache.

    Declaration

    Objective-C

    - (void)keepSynced:(BOOL)keepSynced;

    Parameters

    keepSynced

    Pass true to keep this location synchronized, or false to stop synchronization.

Querying and limiting

  • This method is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryLimited(toFirst:) will respond to at most the first limit child nodes.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryLimitedToFirst:(NSUInteger)limit;

    Parameters

    limit

    The upper bound, inclusive, for the number of child nodes to receive events for

    Return Value

    A DatabaseQuery instance, limited to at most limit child nodes.

  • queryLimited(toLast:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by this method will respond to at most the last limit child nodes.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryLimitedToLast:(NSUInteger)limit;

    Parameters

    limit

    The upper bound, inclusive, for the number of child nodes to receive events for

    Return Value

    A DatabaseQuery instance, limited to at most limit child nodes.

  • This method is used to generate a reference to a view of the data that’s been sorted by the values of a particular child key. This method is intended to be used in combination with queryStarting(atValue:), queryEnding(atValue:), or queryEqual(toValue:).

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryOrderedByChild:(nonnull NSString *)key;

    Parameters

    key

    The child key to use in ordering data visible to the returned DatabaseQuery

    Return Value

    A DatabaseQuery instance, ordered by the values of the specified child key.

  • queryOrdered(byKey:) is used to generate a reference to a view of the data that's been sorted by child key. This method is intended to be used in combination withqueryStarting(atValue:),queryEnding(atValue:), or queryEqual(toValue:)`.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryOrderedByKey;

    Return Value

    A DatabaseQuery instance, ordered by child keys.

  • queryOrdered(byValue:) is used to generate a reference to a view of the data that’s been sorted by child value. This method is intended to be used in combination with queryStarting(atValue:), queryEnding(atValue:), or queryEqual(toValue:).

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryOrderedByValue;

    Return Value

    A DatabaseQuery instance, ordered by child value.

  • queryOrdered(byPriority:) is used to generate a reference to a view of the data that's been sorted by child priority. This method is intended to be used in combination withqueryStarting(atValue:),queryEnding(atValue:), or queryEqual(toValue:)`.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryOrderedByPriority;

    Return Value

    A DatabaseQuery instance, ordered by child priorities.

  • queryStarting(atValue:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryStarting(atValue:) will respond to events at nodes with a value greater than or equal to startValue.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryStartingAtValue:(nullable id)startValue;

    Parameters

    startValue

    The lower bound, inclusive, for the value of data visible to the returned DatabaseQuery

    Return Value

    A DatabaseQuery instance, limited to data with value greater than or equal to startValue

  • queryStarting(atValue:childKey:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryStarting(atValue:childKey:) will respond to events at nodes with a value greater than startValue, or equal to startValue and with a key greater than or equal to childKey. This is most useful when implementing pagination in a case where multiple nodes can match the startValue.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryStartingAtValue:(nullable id)startValue
                                          childKey:
                                              (nullable NSString *)childKey;

    Parameters

    startValue

    The lower bound, inclusive, for the value of data visible to the returned DatabaseQuery
    childKey

    The lower bound, inclusive, for the key of nodes with value equal to startValue

    Return Value

    A DatabaseQuery instance, limited to data with value greater than or equal to startValue

  • queryStarting(afterValue:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryStarting(afterValue:) will respond to events at nodes with a value greater than startAfterValue.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryStartingAfterValue:
    (nullable id)startAfterValue;

    Parameters

    startAfterValue

    The lower bound, exclusive, for the value of data visible to the returned DatabaseQuery

    Return Value

    A DatabaseQuery instance, limited to data with value greater startAfterValue

  • queryStarting(afterValue:childKey:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryStarting(afterValue:childKey:) will respond to events at nodes with a value greater than startAfterValue, or equal to startAfterValue and with a key greater than childKey. This is most useful when implementing pagination in a case where multiple nodes can match the startAfterValue.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)
    queryStartingAfterValue:(nullable id)startAfterValue
                   childKey:(nullable NSString *)childKey;

    Parameters

    startAfterValue

    The lower bound, inclusive, for the value of data visible to the returned DatabaseQuery
    childKey

    The lower bound, exclusive, for the key of nodes with value equal to startAfterValue

    Return Value

    A DatabaseQuery instance, limited to data with value greater than startAfterValue, or equal to startAfterValue with a key greater than childKey

  • queryEnding(atValue:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryEnding(atValue:) will respond to events at nodes with a value less than or equal to endValue.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryEndingAtValue:(nullable id)endValue;

    Parameters

    endValue

    The upper bound, inclusive, for the value of data visible to the returned DatabaseQuery

    Return Value

    A DatabaseQuery instance, limited to data with value less than or equal to endValue

  • queryEnding(atValue:childKey:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryEnding(atValue:childKey:) will respond to events at nodes with a value less than endValue, or equal to endValue and with a key less than or equal to childKey. This is most useful when implementing pagination in a case where multiple nodes can match the endValue.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryEndingAtValue:(nullable id)endValue
                                        childKey:(nullable NSString *)childKey;

    Parameters

    endValue

    The upper bound, inclusive, for the value of data visible to the returned DatabaseQuery
    childKey

    The upper bound, inclusive, for the key of nodes with value equal to endValue

    Return Value

    A DatabaseQuery instance, limited to data with value less than or equal to endValue

  • queryEnding(beforeValue:) is used to generate a reference to a limited view of the data at this location. TheDatabaseQueryinstance returned by queryEnding(beforeValue:)will respond to events at nodes with a value less thanendValue`.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryEndingBeforeValue:(nullable id)endValue;

    Parameters

    endValue

    The upper bound, exclusive, for the value of data visible to the returned DatabaseQuery

    Return Value

    A DatabaseQuery instance, limited to data with value less than endValue

  • queryEnding(beforeValue:childKey:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryEnding(beforeValue:childKey:) will respond to events at nodes with a value less than endValue, or equal to endValue and with a key less than childKey.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryEndingBeforeValue:(nullable id)endValue
                                            childKey:
                                                (nullable NSString *)childKey;

    Parameters

    endValue

    The upper bound, inclusive, for the value of data visible to the returned DatabaseQuery
    childKey

    The upper bound, exclusive, for the key of nodes with value equal to endValue

    Return Value

    A DatabaseQuery instance, limited to data with value less than or equal to endValue

  • queryEqual(toValue:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryEqual(toValue:) will respond to events at nodes with a value equal to the supplied argument.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryEqualToValue:(nullable id)value;

    Parameters

    value

    The value that the data returned by this DatabaseQuery will have

    Return Value

    A DatabaseQuery instance, limited to data with the supplied value.

  • queryEqual(toValue:childKey:) is used to generate a reference to a limited view of the data at this location. The DatabaseQuery instance returned by queryEqual(toValue:childKey:) will respond to events at nodes with a value equal to the supplied argument and with their key equal to childKey. There will be at most one node that matches because child keys are unique.

    Declaration

    Objective-C

    - (nonnull FIRDatabaseQuery *)queryEqualToValue:(nullable id)value
                                       childKey:(nullable NSString *)childKey;

    Parameters

    value

    The value that the data returned by this DatabaseQuery will have
    childKey

    The name of nodes with the right value

    Return Value

    A DatabaseQuery instance, limited to data with the supplied value and the key.

Properties

  • ref

    Gets a DatabaseReference for the location of this query.

    Declaration

    Objective-C

    @property (nonatomic, strong, readonly) FIRDatabaseReference *_Nonnull ref;

    Return Value

    A DatabaseReference for the location of this query.