PTDiffusionUpdateConstraint Class Reference

Introduction

A constraint to be applied to an update operation or the creation of an update stream.

Constraints describe a condition that must be satisfied for an operation to succeed. Constraints can be applied to the setting of a value or creation of an update stream. Constraints are only evaluated on the server.

Constraints are evaluated using the:

• active session locks
• existence of the topic
• current value of the topic

The value of a topic can be described in several ways. The value can be described as an exact value, a partial value or an unset value.

Constraints can be composed with one another using logical ANDs or ORs. It is possible to compose a constraint that can never be satisfied although certain combinations, such as ANDing two incompatible constraints are prevented. Multiple session locks can be held but a topic can only have a single value.

See also

PTDiffusionTopicUpdateFeature

Since

6.3

Inheritance diagram for PTDiffusionUpdateConstraint:

Class Methods
(instancetype)	+ lockedWithLock:
(instancetype)	+ noValue
(instancetype)	+ noTopic
(PTDiffusionPartialJSONUpdateConstraint *)	+ jsonValue

Instance Methods
(nullable instancetype)	- andConstraint:error:
(nullable instancetype)	- orConstraint:error:

Method Documentation

andConstraint:error:

- (nullable instancetype) andConstraint:		(PTDiffusionUpdateConstraint *)	constraint
error:		(NSError **)	error

Returns a composed constraint that represents a logical AND of this constraint and another.

Parameters

constraint	The other constraint that will be logically-ANDed with this constraint
error	Location to store a reason in case of failure. May be nil.

Returns

A new constraint or nil if there was an error.

Exceptions

NSInvalidArgumentException

If the constraint argument is `nil`.

Since

6.3

jsonValue

+ (PTDiffusionPartialJSONUpdateConstraint *) jsonValue

Returns a constraint that partially matches the current topic value.

The topic must be PTDiffusionTopicType_JSON. The returned constraint partially describes the structure of a PTDiffusionJSON value.

Returns

Constraint that partially matches the current topic value.

Since

6.3

lockedWithLock:

+ (instancetype) lockedWithLock:

(PTDiffusionSessionLock *)

lock

Returns a constraint requiring a lock to be held by the session.

This can be used to coordinate operations between multiple sessions.

Parameters

lock	the lock held by the session.

Returns

Constraint requiring a lock to be held by the session.

Exceptions

NSInvalidArgumentException

If the lock argument is `nil`.

Since

6.3

noTopic

+ (instancetype) noTopic

Returns a constraint requiring the path to have no topic.

This is useful when setting the first value of a topic being added using one of the 'add and set' methods without changing the value if the topic already exists. This constraint is unsatisfied if a topic is present at the path.

Returns

Constraint requiring the path to have no topic.

Since

6.3

noValue

+ (instancetype) noValue

Create a constraint requiring the topic to have no value.

This is useful when setting the first value of a topic. This constraint is unsatisfied if a topic is present at the path.

Returns

Constraint requiring the topic to have no value.

Since

6.3

orConstraint:error:

- (nullable instancetype) orConstraint:		(PTDiffusionUpdateConstraint *)	constraint
error:		(NSError **)	error

Returns a composed constraint that represents a logical OR of this constraint and another.

Parameters

constraint	The other constraint that will be logically-ORed with this constraint
error	Location to store a reason in case of failure. May be nil.

Returns

A new constraint or nil if there was an error.

Since

6.10