Class DatasetGraphOne

  • All Implemented Interfaces:
    org.apache.jena.atlas.lib.Closeable, DatasetGraph, Transactional

    public class DatasetGraphOne
    extends DatasetGraphBaseFind
    DatasetGraph of a single graph as default graph.

    Fixed as one graph (the default) - named graphs can not be added nor the default graph changed, only the contents modified.

    This dataset passes transactions down to a nominated backing DatasetGraph.

    It is particular suitable for use with an interference graph.

    • Method Detail

      • 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.
      • commit

        public void commit()
        Description copied from interface: Transactional
        Commit a transaction - finish the transaction and make any changes permanent (if a "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.

      • 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.
      • 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.
      • containsGraph

        public boolean containsGraph​(Node graphNode)
        Description copied from interface: DatasetGraph
        Does the DatasetGraph contain a specific named graph? 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 and this returns true always.
        Specified by:
        containsGraph in interface DatasetGraph
        Overrides:
        containsGraph in class DatasetGraphBase
        Returns:
        boolean
      • 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
      • listGraphNodes

        public java.util.Iterator<Node> listGraphNodes()
        Description copied from interface: DatasetGraph
        Iterate over all names of named graphs
      • prefixes

        public PrefixMap prefixes()
        Description copied from interface: DatasetGraph
        Prefixes for this DatasetGraph
      • close

        public void close()
        Description copied from interface: DatasetGraph
        Close the dataset
        Specified by:
        close in interface org.apache.jena.atlas.lib.Closeable
        Specified by:
        close in interface DatasetGraph
        Overrides:
        close in class DatasetGraphBase