Package org.apache.cayenne

# Interface DataChannel

All Known Subinterfaces:
  `ObjectContext`

All Known Implementing Classes:
  `BaseContext`, `ClientChannel`, `ClientServerChannel`, `DataContext`, `DataDomain`

public interface DataChannel
DataChannel is an abstraction used by ObjectContexts to obtain mapping metadata and access a persistent store. There is rarely a need to use it directly.

Since:
  1.2

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final int`
  `FLUSH_CASCADE_SYNC`
  A synchronization type that results in changes from an ObjectContext to be recorded in the parent DataChannel.
  `static final int`
  `FLUSH_NOCASCADE_SYNC`
  A synchronization type that results in changes from an ObjectContext to be recorded in the parent DataChannel.
  `static final EventSubject`
  `GRAPH_CHANGED_SUBJECT`
  `static final EventSubject`
  `GRAPH_FLUSHED_SUBJECT`
  `static final EventSubject`
  `GRAPH_ROLLEDBACK_SUBJECT`
  `static final int`
  `ROLLBACK_CASCADE_SYNC`
  A synchronization type that results in cascading rollback of changes through the DataChannel stack.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `EntityResolver`
  `getEntityResolver()`
  Returns an EntityResolver instance that contains runtime mapping information.
  `EventManager`
  `getEventManager()`
  Returns an EventManager associated with this channel.
  `QueryResponse`
  `onQuery(ObjectContext originatingContext, Query query)`
  Executes a query, using provided context to register persistent objects if query returns any objects.
  `GraphDiff`
  `onSync(ObjectContext originatingContext, GraphDiff changes, int syncType)`
  Processes synchronization request from a child ObjectContext, returning a GraphDiff that describes changes to objects made on the receiving end as a result of synchronization.

- ## Field Details

  - ### FLUSH_NOCASCADE_SYNC

    static final int FLUSH_NOCASCADE_SYNC
    A synchronization type that results in changes from an ObjectContext to be recorded in the parent DataChannel. If the parent is itself an ObjectContext, changes are NOT propagated any further.
    See Also:
      - Constant Field Values

  - ### FLUSH_CASCADE_SYNC

    static final int FLUSH_CASCADE_SYNC
    A synchronization type that results in changes from an ObjectContext to be recorded in the parent DataChannel. If the parent is itself an ObjectContext, it is expected to send its own sync message to its parent DataChannel to cascade synchronization all the way down the stack.
    See Also:
      - Constant Field Values

  - ### ROLLBACK_CASCADE_SYNC

    static final int ROLLBACK_CASCADE_SYNC
    A synchronization type that results in cascading rollback of changes through the DataChannel stack.
    See Also:
      - Constant Field Values

  - ### GRAPH_CHANGED_SUBJECT

    static final EventSubject GRAPH_CHANGED_SUBJECT

  - ### GRAPH_FLUSHED_SUBJECT

    static final EventSubject GRAPH_FLUSHED_SUBJECT

  - ### GRAPH_ROLLEDBACK_SUBJECT

    static final EventSubject GRAPH_ROLLEDBACK_SUBJECT

- ## Method Details

  - ### getEventManager

    EventManager getEventManager()
    Returns an EventManager associated with this channel. Channel may return null if EventManager is not available for any reason.

  - ### getEntityResolver

    EntityResolver getEntityResolver()
    Returns an EntityResolver instance that contains runtime mapping information.

  - ### onQuery

    QueryResponse onQuery(ObjectContext originatingContext, Query query)
    Executes a query, using provided context to register persistent objects if query returns any objects.
    Parameters:
      `originatingContext` - an ObjectContext that originated the query, used to register result objects.
    Returns:
      a generic response object that encapsulates result of the execution.

  - ### onSync

    GraphDiff onSync(ObjectContext originatingContext, GraphDiff changes, int syncType)
    Processes synchronization request from a child ObjectContext, returning a GraphDiff that describes changes to objects made on the receiving end as a result of synchronization.
    Parameters:
      `originatingContext` - an ObjectContext that initiated the sync. Can be null.
      `changes` - diff from the context that initiated the sync.
      `syncType` - One of `FLUSH_NOCASCADE_SYNC`, `FLUSH_CASCADE_SYNC`, `ROLLBACK_CASCADE_SYNC`.