Inherits From:
NSObject
Inherits From:
com.apple.yellow.eoaccess
Class Description
An EODatabaseChannel represents an independent communication channel to the database server. It's associated with an EODatabaseContext and an EODatabase, which, together with the EODatabaseChannel, form the database level of Enterprise Objects Framework's access layer. See the EODatabase class specification for more information.
An EODatabaseChannel has an EOAdaptorChannel that it uses to connect to the database server its EODatabase object represents. An EODatabaseChannel fetches database records as instances of enterprise object classes that are specified in its EODatabase's EOModel objects. An EODatabaseChannel also has an EODatabaseContext, which uses the channel to perform fetches and to lock rows in the database. All of the database level objects are used automatically by EOEditingContexts and other components of Enterprise Objects Framework. You rarely need to interact with them directly. In particular, you wouldn't ordinarily use an EODatabaseChannel to fetch objects. Rather, you'd use an EOEditingContext.
EODatabaseChannel
()
public EODatabaseChannel
(com.apple.yellow.eocontrol.EODatabaseContext aDatabaseContext)
Creates and returns a new EODatabaseChannel. Typically, you don't need to programmatically create EODatabaseChannel objects. Rather, they are created automatically by the control layer. See the EODatabase class description for more information.
aDatabaseContext is assigned to the new EODatabaseChannel as the DatabaseContext in which the channel works. The new EODatabaseChannel creates an AdaptorChannel with which to communicate with the database server. The constructor throws an exception if the underlying adaptor context can't create a corresponding adaptor channel.
See also:
databaseContext
, adaptorChannel
Instance Methods
adaptorChannel
public com.apple.yellow.eocontrol.EOAdaptorChannel adaptorChannel
()
Returns the EOAdaptorChannel used by the receiver for communication with the database server.
See also: "Constructors"
cancelFetch
public void cancelFetch
Cancels any fetch in progress.
See also:
isFetchInProgress
, selectObjectsWithFetchSpecification
, fetchObject
databaseContext
public com.apple.yellow.eocontrol.EODatabaseContext databaseContext
()
Returns the EODatabaseContext that controls transactions for the receiver.
See also: "Constructors"
delegate
public java.lang.Object delegate
()
Returns the receiver's delegate. An EODatabaseChannel shares the delegate of its EODatabaseContext. See the EODatabaseContext class specification for the delegate methods you can implement.
See also:
setDelegate
fetchObject
public java.lang.Object fetchObject
()
Fetches and returns the next object in the result set produced by a selectObjectsWithFetchSpecification
message; returns null
if there are no more objects in the current result set or if an error occurs. This method uses the receiver's EOAdaptorChannel to fetch a row, records a snapshot with the EODatabaseContext if necessary, and creates an enterprise object from the row if a corresponding object doesn't already exist. The new object is sent an awakeFromFetchInEditingContext:
message to allow it to finish setting up its state.
If no snapshot exists for the fetched object, the receiver sends its EODatabase a recordSnapshot:forGlobalID:
message to record one. If a snapshot already exists (because the object was previously fetched), the receiver checks whether it should overwrite the old snapshot with the new one. It does so by asking the delegate with a databaseContextShouldUpdateCurrentSnapshot
method. If the delegate doesn't respond to this method, the EODatabaseChannel overwrites the snapshot if it's locking or refreshing fetched objects. Further, if the EODatabaseChannel is refreshing fetched objects, it posts an EOObjectsChangedInStoreNotification on behalf of its EODatabaseContext (which causes any EOEditingContext using that EODatabaseContext to update its enterprise object with the values recorded in the new snapshot).
For information on locking and update strategies, see the EODatabaseContext class specification. For information on refreshing fetched objects, see the EOFetchSpecification class specification.
Ordinarily, you don't directly use an EODatabaseChannel to fetch objects. Rather, you use an EOEditingContext, which uses an underlying EODatabaseChannel to do its work.
See also:
cancelFetch
, isFetchInProgress
, isLocking
, isRefreshingObjects
isFetchInProgress
public boolean isFetchInProgress
Returns true
if the receiver is fetching, false
otherwise. An EODatabaseChannel is fetching if it's been sent a successful selectObjectsWithFetchSpecification
message. An EODatabaseChannel stops fetching when there are no more objects to fetch or when it is sent a cancelFetch
message.
isLocking
public boolean isLocking()
Returns true
if the receiver is locking the objects selected, as determined by its EODatabaseContext's update strategy or the EOFetchSpecification used to perform the select. Returns false
otherwise. This method always returns false
when no fetch is in progress.
See also:
- locksObjects
(EOFetchSpecification), setIsLocking
isRefreshingObjects
public boolean isRefreshingObject
s()
Returns true
if the receiver overwrites existing snapshots with fetched values and causes the current EOEditingContext to overwrite existing enterprise objects with those values as well. Returns false
otherwise. This behavior is controlled by the EOFetchSpecification used in a selectObjectsWithFetchSpecification
message.
See also:
- refreshesRefetchedObjects
(EOFetchSpecification), fetchObject
, setIsRefreshingObjects
selectObjectsWithFetchSpecification
public void selectObjectsWithFetchSpecification
(
com.apple.yellow.eocontrol.EOFetchSpecification fetchSpecification, com.apple.yellow.eocontrol.EOEditingContext anEditingContext)
Selects objects described by fetchSpecification so that they'll be fetched into anEditingContext. The selected objects compose one or more result sets, each object of which will be returned by subsequent fetchObject
messages in the order prescribed by fetchSpecification's EOSortOrderings.
Throws an exception if an error occurs; the particular exception depends on the specific error, and is indicated in the exception's description. Some possible reasons for failure are:
databaseContextShouldSelectObjects
, databaseContextShouldUsePessimisticLockWithFetchSpecification
, and databaseContextDidSelectObjects
. See their descriptions in the EODatabaseContext class specification for more information.You wouldn't ordinarily invoke this method directly; rather, you'd use an EOEditingContext to select and fetch enterprise objects.
See also:
fetchObject
setCurrentEditingContext
public void setCurrentEditingContext
(com.apple.yellow.eocontrol.EOEditingContext anEditingContext)
Sets the EOEditingContext that's made the owner of fetched objects to anEditingContext. This method is automatically invoked by selectObjectsWithFetchSpecification
. You should never invoke it directly.
See also:
setCurrentEntity
setCurrentEntity
public void setCurrentEntity
(EOEntity anEntity)
Sets the EOEntity used when fetching enterprise objects to anEntity. Subsequent fetchObject
messages during a fetch operation create an object of the class associated with anEntity. This method is invoked automatically by selectObjectsWithFetchSpecification
.You should never need to invoke it directly.
See also:
setCurrentEditingContext
setDelegate
public void setDelegate
(java.lang.Object anObject)
Sets the receiver's delegate to anObject. An EODatabaseChannel shares the delegate of its EODatabaseContext; you should never invoke this method directly. See the EODatabaseContext class specification for the delegate methods you can implement.
See also:
delegate
setIsLocking
public void setIsLocking
(boolean flag)
Records whether the receiver locks the records it selects. A EODatabaseChannel modifies its interaction with the database server and its snapshotting behavior based on this setting. If flag is true
the EODatabaseChannel modifies its fetching behavior to lock objects; if flag is false
it simply fetches them.
An EODatabaseChannel automatically sets this flag according to the fetch specification used in a selectObjectsWithFetchSpecification
message. You might invoke this method directly if evaluating SQL directly with EOAdaptorChannel's evaluateExpression
method.
See also:
- locksObjects
(EOFetchSpecification), setIsLocking
setIsRefreshingObjects
public void setIsRefreshingObjects
(boolean flag)
Records whether the receiver causes existing snapshots and enterprise objects to be overwritten with fetched values. If flag is true
the receiver overwrites existing snapshots with fetched values and posts an ObjectsChangedInStoreNotification on behalf of its EODatabaseContext (which typically causes the an existing object's EOEditingContext to replace its values with the new ones). If flag is false
, the receiver relies on the delegate to determine whether snapshots should be overwritten, and doesn't cause enterprise objects to be overwritten.
An EODatabaseChannel automatically sets this flag according to the fetch specification used in a selectObjectsWithFetchSpecification
message. You might invoke this method directly if evaluating SQL directly with EOAdaptorChannel's evaluateExpression:
method.
See also:
- refreshesRefetchedObjects
(EOFetchSpecification)