org.apache.jena.sparql.core

Class DatasetGraphNull

java.lang.Object

org.apache.jena.sparql.core.DatasetGraphBase

org.apache.jena.sparql.core.DatasetGraphBaseFind

org.apache.jena.sparql.core.DatasetGraphNull

All Implemented Interfaces:

org.apache.jena.atlas.lib.Closeable, DatasetGraph, Transactional

Direct Known Subclasses:

DatasetGraphSink, DatasetGraphZero

public abstract class DatasetGraphNull
extends DatasetGraphBaseFind

A DatasetGraph class for support of DatasetGraphs that do nothing.

• No named graphs.
• Empty default graph.
• Empty union graph.
• No update. (DatasetGraphSink overrides this)

See Also:

DatasetGraphSink, DatasetGraphZero

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.jena.sparql.core.Transactional

Transactional.Promote

Method Summary

Modifier and Type	Method and Description
void	abort() Abort a transaction - finish the transaction and undo any changes (if a "write" transaction)
void	add(Quad quad) Add a quad
void	addGraph(Node graphName, Graph graph) Add the given graph to the dataset.
void	begin() Start a transaction which is READ mode and which will switch to WRITE if an update is attempted but only if no intermediate transaction has performed an update.
void	begin(ReadWrite mode) Start either a READ or WRITE transaction.
void	begin(TxnType txnType) Start a transaction. READ or WRITE transactions start in that state and do not change for the lifetime of the transaction.
void	commit() Commit a transaction - finish the transaction and make any changes permanent (if a "write" transaction)
void	delete(Quad quad) Delete a quad
void	deleteAny(Node g, Node s, Node p, Node o) Delete any quads matching the pattern
void	end() Finish the transaction - if a write transaction and commit() has not been called, then abort
Graph	getDefaultGraph() Get the default graph as a Jena Graph
Graph	getGraph(Node graphNode) Get the graph named by graphNode : returns null when there is no such graph.
Graph	getUnionGraph() Return a Graph that is the union of all named graphs in this dataset.
boolean	isInTransaction() Say whether inside a transaction.
Iterator<Node>	listGraphNodes() Iterate over all names of named graphs
boolean	promote(Transactional.Promote txnType) Attempt to promote a transaction from "read" mode to "write" and the transaction.
void	removeGraph(Node graphName) Remove all data associated with the named graph.
void	setDefaultGraph(Graph g) Set the default graph.
boolean	supportsTransactionAbort() Declare whether Transactional.abort() is supported.
boolean	supportsTransactions() A DatasetGraph supports transactions if it provides Transactional.begin()/ Transactional.commit()/Transactional.end().
ReadWrite	transactionMode() Return the current mode of the transaction - "read" or "write".
TxnType	transactionType() Return the transaction type used in begin(TxnType).

Methods inherited from class org.apache.jena.sparql.core.DatasetGraphBaseFind

find, findInUnionGraph, findNG, findQuadsInUnionGraph

Methods inherited from class org.apache.jena.sparql.core.DatasetGraphBase

add, clear, close, contains, contains, containsGraph, delete, deleteAny, find, find, getContext, getLock, isEmpty, size, toString

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.jena.sparql.core.Transactional

promote

Method Detail

begin

public void begin()

Description copied from interface: Transactional

Start a transaction which is READ mode and which will switch to WRITE if an update is attempted but only if no intermediate transaction has performed an update.

See Transactional.begin(TxnType) for more details an options.

May not be implemented. See Transactional.begin(ReadWrite) is guaranteed to be provided.

begin

public void begin(TxnType txnType)

Description copied from interface: Transactional

Start a transaction.
READ or WRITE transactions start in that state and do not change for the lifetime of the transaction.

• WRITE: this guarantees a WRITE will complete if commit() is called. The same as begin(ReadWrite.WRITE).
• READ: the transaction can not promote to WRITE,ensuring read-only access to the data. The same as begin(ReadWrite.READ).
• READ_PROMOTE: the transaction will go from "read" to "write" if an update is attempted and if the dataset has not been changed by another write transaction. See also Transactional.promote().
• READ_COMMITTED_PROMOTE: Use this with care. The promotion will succeed but changes from other transactions become visible.

Read committed: at the point transaction attempts promotion from "read" to "write", the system checks if the dataset has change since the transaction started (called begin). If READ_PROMOTE, the dataset must not have changed; if READ_COMMITTED_PROMOTE any intermediate changes are visible but the application can not assume any data it has read in the transaction is the same as it was at the point the transaction started.

This operation is optional and some implementations may throw a JenaTransactionException exception for some or all TxnType values.

See Transactional.begin(ReadWrite) for a form that is required of implementations.

begin

public void begin(ReadWrite mode)

Description copied from interface: Transactional

Start either a READ or WRITE transaction.

promote

public boolean promote(Transactional.Promote txnType)

Description copied from interface: Transactional

Attempt to promote a transaction from "read" mode to "write" and the transaction. This method allows the form of promotion to be specified. The transaction must not have been started with READ, which is read-only.

An argument of READ_PROMOTE treats the promotion as if the transaction was started with READ_PROMOTE (any other writer commiting since the transaction started blocks promotion) and READ_COMMITTED_PROMOTE treats the promotion as if the transaction was started with READ_COMMITTED_PROMOTE (intemediate writer commits become visible).

Returns "true" if the transaction is in write mode after the call. The method always succeeds of the transaction is already "write".

This method returns true if a READ_PROMOTE or READ_COMMITTED_PROMOTE is promoted.

This method returns false if a READ_PROMOTE can't be promoted - the transaction is still valid and in "read" mode.

This method throws an exception if there is an attempt to promote a READ transaction.

commit

public void commit()

Description copied from interface: Transactional

Commit a transaction - finish the transaction and make any changes permanent (if a "write" transaction)

abort

public void abort()

Description copied from interface: Transactional

Abort a transaction - finish the transaction and undo any changes (if a "write" transaction)

isInTransaction

public boolean isInTransaction()

Description copied from interface: Transactional

Say whether inside a transaction.

end

public void end()

Description copied from interface: Transactional

Finish the transaction - if a write transaction and commit() has not been called, then abort

transactionMode

public ReadWrite transactionMode()

Description copied from interface: Transactional

Return the current mode of the transaction - "read" or "write". If the caller is not in a transaction, this method returns null.

transactionType

public TxnType transactionType()

Description copied from interface: Transactional

Return the transaction type used in begin(TxnType). If the caller is not in a transaction, this method returns null.

supportsTransactions

public boolean supportsTransactions()

Description copied from interface: DatasetGraph

A DatasetGraph supports transactions if it provides Transactional.begin()/ Transactional.commit()/Transactional.end(). The core storage DatasetGraphs provide fully serialized transactions. A DatasetGraph that provides functionality across independent systems can not provide such strong guarantees. For example, it may use MRSW locking and some isolation control. Specifically, it would not necessarily provide Transactional.abort().

See DatasetGraph.supportsTransactionAbort() for Transactional.abort(). In addition, check details of a specific implementation.

supportsTransactionAbort

public boolean supportsTransactionAbort()

Description copied from interface: DatasetGraph

Declare whether Transactional.abort() is supported. This goes along with clearing up after exceptions inside application transaction code.

listGraphNodes

public Iterator<Node> listGraphNodes()

Description copied from interface: DatasetGraph

Iterate over all names of named graphs

getDefaultGraph

public Graph getDefaultGraph()

Description copied from interface: DatasetGraph

Get the default graph as a Jena Graph

Specified by:

getDefaultGraph in interface DatasetGraph

Specified by:

getDefaultGraph in class DatasetGraphBase

getUnionGraph

public Graph getUnionGraph()

Description copied from interface: DatasetGraph

Return a Graph that is the union of all named graphs in this dataset. This union graph is read-only (its prefix mapping in the current JVM may be changed but that may not persist).

Specified by:

getUnionGraph in interface DatasetGraph

Overrides:

getUnionGraph in class DatasetGraphBase

getGraph

public Graph getGraph(Node graphNode)

Description copied from interface: DatasetGraph

Get the graph named by graphNode : returns null when there is no such graph. NB Whether a dataset contains a graph if there are no triples is not defined - see the specific implementation. Some datasets are "open" - they have all graphs even if no triples.

Specified by:

getGraph in interface DatasetGraph

Specified by:

getGraph in class DatasetGraphBase

add

public void add(Quad quad)

Description copied from interface: DatasetGraph

Add a quad

Specified by:

add in interface DatasetGraph

Overrides:

add in class DatasetGraphBase

delete

public void delete(Quad quad)

Description copied from interface: DatasetGraph

Delete a quad

Specified by:

delete in interface DatasetGraph

Overrides:

delete in class DatasetGraphBase

deleteAny

public void deleteAny(Node g,
                      Node s,
                      Node p,
                      Node o)

Description copied from interface: DatasetGraph

Delete any quads matching the pattern

Specified by:

deleteAny in interface DatasetGraph

Overrides:

deleteAny in class DatasetGraphBase

setDefaultGraph

public void setDefaultGraph(Graph g)

Description copied from interface: DatasetGraph

Set the default graph. Set the active graph if it was null. This replaces the contents default graph, not merge data into it. Do not assume that the same object is returned by DatasetGraph.getDefaultGraph()

Specified by:

setDefaultGraph in interface DatasetGraph

Overrides:

setDefaultGraph in class DatasetGraphBase

addGraph

public void addGraph(Node graphName,
                     Graph graph)

Description copied from interface: DatasetGraph

Add the given graph to the dataset. Replaces any existing data for the named graph; to add data, get the graph and add triples to it, or add quads to the dataset. Do not assume that the same Java object is returned by DatasetGraph.getGraph(org.apache.jena.graph.Node)

Specified by:

addGraph in interface DatasetGraph

Specified by:

addGraph in class DatasetGraphBase

removeGraph

public void removeGraph(Node graphName)

Description copied from interface: DatasetGraph

Remove all data associated with the named graph. This will include prefixes associated with the graph.

Specified by:

removeGraph in interface DatasetGraph

Specified by:

removeGraph in class DatasetGraphBase