Examples of org.eclipse.persistence.queries.ValueReadQuery

org.eclipse.persistence.queries.ValueReadQuery

Purpose: Concrete class to perform a read of a single data value.

Responsibilities: Used in conjunction with CursoredStream size and Platform getSequence. This can be used to read a single data value (i.e. one field). A single data value is returned, or null if no rows are returned. @author James Sutherland @since TOPLink/Java 1.2

    /**
     * INTERNAL:
     * Build the identity query for native sequencing.
     */
    public ValueReadQuery buildSelectQueryForIdentity() {
        ValueReadQuery selectQuery = new ValueReadQuery();
        StringWriter writer = new StringWriter();
        writer.write("SELECT @@IDENTITY");
        selectQuery.setSQLString(writer.toString());
        return selectQuery;
    }

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     * and returns it. 
     * @param qualifiedSeqName known by TimesTen to be a defined sequence
     */
    @Override
    public ValueReadQuery buildSelectQueryForSequenceObject(String qualifiedSeqName, Integer size) {
        return new ValueReadQuery("SELECT " + qualifiedSeqName + ".NEXTVAL FROM DUAL");
    }

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     * TimesTen uses the Oracle syntax for getting the current timestamp.
     */
    @Override
    public ValueReadQuery getTimestampQuery() {
        if (this.timestampQuery == null) {
            this.timestampQuery = new ValueReadQuery();
            this.timestampQuery.setSQLString("SELECT SYSDATE FROM DUAL");
        }
        return this.timestampQuery;
    }

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     * from Oracle.
     * In order to execute this query a database administrator may need
     * to grant execute permission on pl/sql package DBMS_FLASHBACK.
     */
    public ValueReadQuery getSystemChangeNumberQuery() {
        ValueReadQuery sCNQuery = new ValueReadQuery();
        sCNQuery.setSQLString("SELECT DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER FROM DUAL");
        return sCNQuery;
    }

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     * This method returns the query to select the timestamp
     * from the server for Oracle.
     */
    public ValueReadQuery getTimestampQuery() {
        if (timestampQuery == null) {
            timestampQuery = new ValueReadQuery();
            timestampQuery.setSQLString("SELECT SYSDATE FROM DUAL");
        }
        return timestampQuery;
    }

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     * Produce a DataReadQuery which updates(!) the sequence number in the db
     * and returns it. Currently implemented on Oracle only.
     * @param qualifiedSeqName known by Oracle to be a defined sequence
     */
    public ValueReadQuery buildSelectQueryForSequenceObject(String qualifiedSeqName, Integer size) {
        return new ValueReadQuery("SELECT " + qualifiedSeqName + ".NEXTVAL FROM DUAL");
    }

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     * Though Oracle doesn't support identity it could be imitated,
     * see comment to setSupportsIdentity method.
     * @param qualifiedSeqName known by Oracle to be a defined sequence
     */
    public ValueReadQuery buildSelectQueryForIdentity(String qualifiedSeqName, Integer size) {
        return new ValueReadQuery("SELECT " + qualifiedSeqName + ".CURRVAL FROM DUAL");
    }

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     * server for Postgres.
     */
    @Override
    public ValueReadQuery getTimestampQuery() {
        if (this.timestampQuery == null) {
            this.timestampQuery = new ValueReadQuery();
            this.timestampQuery.setSQLString("SELECT NOW()");
        }
        return this.timestampQuery;


    }

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     * the platform supportsIdentity then (at least) one of
     * buildSelectQueryForIdentity methods should return non-null query.
     */
    @Override
    public ValueReadQuery buildSelectQueryForIdentity() {
        ValueReadQuery selectQuery = new ValueReadQuery();
        selectQuery.setSQLString("select lastval()");
        return selectQuery;
    }

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     * one of buildSelectQueryForSequenceObject methods should return non-null
     * query.
     */
    @Override
    public ValueReadQuery buildSelectQueryForSequenceObject(String qualifiedSeqName, Integer size) {
        return new ValueReadQuery("select nextval(\'" + qualifiedSeqName + "\')");
    }

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