firebase::database::Query

#include <query.h>

The Query class is used for reading data.

Summary

Listeners can be attached, which will be triggered when the data changes.

Inheritance

Direct Known Subclasses:firebase::database::DatabaseReference

Constructors and Destructors
Query()
Default constructor.
Query(const Query & query)
Copy constructor.
Query(Query && query)
Move constructor.
~Query()
Required virtual destructor.

Public functions
AddChildListener(ChildListener *listener)
void
Adds a listener that will be called any time a child is added, removed, modified, or reordered.
AddValueListener(ValueListener *listener)
void
Adds a listener that will be called immediately and then again any time the data changes.
EndAt(Variant order_value)
Get a Query constrained to nodes with the given sort value or lower.
EndAt(Variant order_value, const char *child_key)
Get a Query constrained to nodes with the given sort value or lower, and the given key or lower.
EqualTo(Variant order_value)
Get a Query constrained to nodes with the exact given sort value.
EqualTo(Variant order_value, const char *child_key)
Get a Query constrained to nodes with the exact given sort value, and the exact given key.
GetReference() const
Gets a DatabaseReference corresponding to the given location.
GetValue()
Gets the value of the query for the given location a single time.
GetValueLastResult()
Gets the result of the most recent call to GetValue().
LimitToFirst(size_t limit)
Gets a Query limited to only the first results.
LimitToLast(size_t limit)
Gets a Query limited to only the last results.
OrderByChild(const char *path)
Gets a query in which child nodes are ordered by the values of the specified path.
OrderByChild(const std::string & path)
Gets a query in which child nodes are ordered by the values of the specified path.
OrderByKey()
Gets a query in which child nodes are ordered by their keys.
OrderByPriority()
Gets a query in which child nodes are ordered by their priority.
OrderByValue()
Create a query in which nodes are ordered by their value.
RemoveAllChildListeners()
void
Removes all child listeners that were added by AddChildListener().
RemoveAllValueListeners()
void
Removes all value listeners that were added with AddValueListener().
RemoveChildListener(ChildListener *listener)
void
Removes a listener that was previously added with AddChildListener().
RemoveValueListener(ValueListener *listener)
void
Removes a listener that was previously added with AddValueListener().
SetKeepSynchronized(bool keep_sync)
void
Sets whether this location's data should be kept in sync even if there are no active Listeners.
StartAt(Variant order_value)
Get a Query constrained to nodes with the given sort value or higher.
StartAt(Variant order_value, const char *child_key)
Get a Query constrained to nodes with the given sort value or higher, and the given key or higher.
is_valid() const
virtual bool
Returns true if this query is valid, false if it is not valid.
operator=(const Query & query)
Copy assignment operator.
operator=(Query && query)
Move assignment operator.

Public functions

AddChildListener

void AddChildListener(
  ChildListener *listener
)

Adds a listener that will be called any time a child is added, removed, modified, or reordered.

Details
Parameters
listener
A ChildListener instance, which must remain in memory until you remove the listener from the Query.

AddValueListener

void AddValueListener(
  ValueListener *listener
)

Adds a listener that will be called immediately and then again any time the data changes.

Details
Parameters
listener
A ValueListener instance, which must remain in memory until you remove the listener from the Query.

EndAt

Query EndAt(
  Variant order_value
)

Get a Query constrained to nodes with the given sort value or lower.

This method is used to generate a reference to a limited view of the data at this location. The Query returned will only refer to child nodes with a value less than or equal to the given value, using the given OrderBy directive (or priority as default).

Details
Parameters
order_value
The highest sort value the Query should refer to.
Returns
A Query in this same location, filtering out child nodes that have a higher sort value or key than the sort value or key specified.

EndAt

Query EndAt(
  Variant order_value,
  const char *child_key
)

Get a Query constrained to nodes with the given sort value or lower, and the given key or lower.

This method is used to generate a reference to a limited view of the data at this location. The Query returned will only refer to child nodes with a value less than or equal to the given value, using the given OrderBy directive (or priority as default), and additionally only child nodes with a key less than or equal to the given key.

Known issue This currently does not work properly on all platforms. Please use EndAt(Variant order_value) instead.

Details
Parameters
order_value
The highest sort value the Query should include.
child_key
The highest key the Query should include.
Returns
A Query in this same location, filtering out child nodes that have a higher sort value than the sort value specified, or a higher key than the key specified.

EqualTo

Query EqualTo(
  Variant order_value
)

Get a Query constrained to nodes with the exact given sort value.

This method is used to create a query constrained to only return child nodes with the given value, using the given OrderBy directive (or priority as default).

Details
Parameters
order_value
The exact sort value the Query should include.
Returns
A Query in this same location, filtering out child nodes that have a different sort value than the sort value specified.

EqualTo

Query EqualTo(
  Variant order_value,
  const char *child_key
)

Get a Query constrained to nodes with the exact given sort value, and the exact given key.

This method is used to create a query constrained to only return the child node with the given value, using the given OrderBy directive (or priority as default), and the given key. Note that there is at most one such child as child key names are unique.

Known issue This currently does not work properly on iOS and desktop. Please use EqualTo(Variant order_value) instead.

Details
Parameters
order_value
The exact sort value the Query should include.
child_key
The exact key the Query should include.
Returns
A Query in this same location, filtering out child nodes that have a different sort value than the sort value specified, and containing at most one child with the exact key specified.

GetReference

DatabaseReference GetReference() const

Gets a DatabaseReference corresponding to the given location.

Details
Returns
A DatabaseReference corresponding to the same location as the Query, but without any of the ordering or filtering parameters.

GetValue

Future< DataSnapshot > GetValue()

Gets the value of the query for the given location a single time.

This is an asynchronous operation which takes time to execute, and uses firebase::Future to return its result.

Details
Returns
A Future result, which will complete when the operation either succeeds or fails. On this Future's completion, if its Error is kErrorNone, the operation succeeded, and the DataSnapshot contains the data in this location.

GetValueLastResult

Future< DataSnapshot > GetValueLastResult()

Gets the result of the most recent call to GetValue().

Details
Returns
Result of the most recent call to GetValue().

LimitToFirst

Query LimitToFirst(
  size_t limit
)

Gets a Query limited to only the first results.

Limits the query to reference only the first N child nodes, using the given OrderBy directive (or priority as default).

Details
Parameters
limit
Number of children to limit the Query to.
Returns
A Query in this same location, limited to the specified number of children (taken from the beginning of the sorted list).

LimitToLast

Query LimitToLast(
  size_t limit
)

Gets a Query limited to only the last results.

Details
Parameters
limit
Number of children to limit the Query to.
Returns
A Query in this same location, limited to the specified number of children (taken from the end of the sorted list).

OrderByChild

Query OrderByChild(
  const char *path
)

Gets a query in which child nodes are ordered by the values of the specified path.

Any previous OrderBy directive will be replaced in the returned Query.

Details
Parameters
path
Path to a child node. The value of this node will be used for sorting this query. The pointer you pass in need not remain valid after the call completes.
Returns
A Query in this same location, with the children are sorted by the value of their own child specified here.

OrderByChild

Query OrderByChild(
  const std::string & path
)

Gets a query in which child nodes are ordered by the values of the specified path.

Any previous OrderBy directive will be replaced in the returned Query.

Details
Parameters
path
Path to a child node. The value of this node will be used for sorting this query.
Returns
A Query in this same location, with the children are sorted by the value of their own child specified here.

OrderByKey

Query OrderByKey()

Gets a query in which child nodes are ordered by their keys.

Any previous OrderBy directive will be replaced in the returned Query.

Details
Returns
A Query in this same location, with the children are sorted by their key.

OrderByPriority

Query OrderByPriority()

Gets a query in which child nodes are ordered by their priority.

Any previous OrderBy directive will be replaced in the returned Query.

Details
Returns
A Query in this same location, with the children are sorted by their priority.

OrderByValue

Query OrderByValue()

Create a query in which nodes are ordered by their value.

Details
Returns
A Query in this same location, with the children are sorted by their value.

Query

 Query()

Default constructor.

This creates an invalid Query. Attempting to perform any operations on this reference will fail unless a valid Query has been assigned to it.

Query

 Query(
  const Query & query
)

Copy constructor.

Queries can be copied. Copies exist independently of each other.

Query

 Query(
  Query && query
)

Move constructor.

RemoveAllChildListeners

void RemoveAllChildListeners()

Removes all child listeners that were added by AddChildListener().

Note:You can remove ChildListeners from a different Query than you added them to, as long as the two Query instances are equivalent.

RemoveAllValueListeners

void RemoveAllValueListeners()

Removes all value listeners that were added with AddValueListener().

Note:You can remove ValueListeners from a different Query than you added them to, as long as the two Query instances are equivalent.

RemoveChildListener

void RemoveChildListener(
  ChildListener *listener
)

Removes a listener that was previously added with AddChildListener().

Note:You can remove a ChildListener from a different Query than you added it to, as long as the two Query instances are equivalent.

Details
Parameters
listener
A ChildListener instance to remove from the Query. After it is removed, you can delete it or attach it to a new location.

RemoveValueListener

void RemoveValueListener(
  ValueListener *listener
)

Removes a listener that was previously added with AddValueListener().

Note:You can remove a ValueListener from a different Query than you added it to, as long as the two Query instances are equivalent.

Details
Parameters
listener
A ValueListener instance to remove from the Query. After it is removed, you can delete it or attach it to a new location.

SetKeepSynchronized

void SetKeepSynchronized(
  bool keep_sync
)

Sets whether this location's data should be kept in sync even if there are no active Listeners.

By calling SetKeepSynchronized(true) on a given database 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.

Details
Parameters
keep_sync
If true, set this location to be synchronized. If false, set it to not be synchronized.

StartAt

Query StartAt(
  Variant order_value
)

Get a Query constrained to nodes with the given sort value or higher.

This method is used to generate a reference to a limited view of the data at this location. The Query returned will only refer to child nodes with a value greater than or equal to the given value, using the given OrderBy directive (or priority as the default).

Details
Parameters
order_value
The lowest sort value the Query should include.
Returns
A Query in this same location, filtering out child nodes that have a lower sort value than the sort value specified.

StartAt

Query StartAt(
  Variant order_value,
  const char *child_key
)

Get a Query constrained to nodes with the given sort value or higher, and the given key or higher.

This method is used to generate a reference to a limited view of the data at this location. The Query returned will only refer to child nodes with a value greater than or equal to the given value, using the given OrderBy directive (or priority as default), and additionally only child nodes with a key greater than or equal to the given key.

Known issue This currently does not work properly on all platforms. Please use StartAt(Variant order_value) instead.

Details
Parameters
order_value
The lowest sort value the Query should include.
child_key
The lowest key the Query should include.
Returns
A Query in this same location, filtering out child nodes that have a lower sort value than the sort value specified, or a lower key than the key specified.

is_valid

virtual bool is_valid() const

Returns true if this query is valid, false if it is not valid.

An invalid query could be returned by, say, attempting to OrderBy two different items, or calling OrderByChild() with an empty path, or by constructing a Query with the default constructor. If a Query is invalid, attempting to add more constraints will also result in an invalid Query.

Details
Returns
true if this query is valid, false if this query is invalid.

operator=

Query operator=(
  const Query & query
)

Copy assignment operator.

Queries can be copied. Copies exist independently of each other.

operator=

Query operator=(
  Query && query
)

Move assignment operator.

~Query

virtual  ~Query()

Required virtual destructor.

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