What is a PushTopic?

A PushTopic is record that

1. Defines a channel.

2. Determines what events will cause a notification. Event is a modification of a field while creating, updating, deleting or undeleting a record.

3. Describes the data the notification will contain.

Used in Streaming API.

NotifyForFields is used to determine when notification should be sent. NotifyForFields in PushTopic values.

1. All - considers changes in all fields.
2. Referenced - considers changes in fields in both SELECT and WHERE clauses.
3. SELECT - considers changes in fields in SELECT clause.
4. WHERE - considers changes in fields in WHERE clause.

Query limitation in PushTopic

1. Relationship reference is not supported. Example: SELECT Id, ABC__r.Name.

2. Sub Query is not supported. Example SELECT Id, (SELECT Name FROM ABC__r).

Supported CometD methods

1. handshake - for long polling connection

2. subscribe - subscribes to a channel

3. unsubscribe - un subscribes to a channel

4. disconnect - breaks connection

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