Bug 416703 Mongodb : Display correctly the Number data type
data/org.eclipse.birt.data.oda.mongodb/src/org/eclipse/birt/data/oda/mongodb/internal/impl/MDbMetaData.java
return m_connectedDB.getCollectionFromString( collectionName );
    }
    /**
     * Returns all fields' name and corresponding metadata found in the specified collection.
     * @param collectionName name of MongoDB collection (i.e. table)
     * @param searchLimit maximum number of documents, i.e. rows to search for available fields;
     *          a zero or negative value would adopt the default limit 
     * @param runtimeProps  an instance of QueryProperties containing the data set runtime property values;
     *          may be null to apply all default values in finding the available fields metadata
     * @return  the DocumentsMetaData object that contains the list of available field names and 
     *          corresponding metadata; 
     *          an empty list is returned if no available fields are found, or 
     *          if the specified collection does not exist
     * @throws OdaException
     */
    public DocumentsMetaData getAvailableFields( String collectionName, 
            int searchLimit, QueryProperties runtimeProps )
        throws OdaException
    {
        DBCollection collection = getCollection( collectionName );
        if( collection == null && ! runtimeProps.hasRunCommand() )
        {
            if( runtimeProps.getOperationType() == CommandOperationType.RUN_DB_COMMAND &&
                runtimeProps.getOperationExpression().isEmpty() )
                throw new OdaException( 
                    Messages.bind( Messages.mDbMetaData_missingCmdExprText, runtimeProps.getOperationType().displayName() ));
            else
                throw new OdaException( 
                    Messages.bind( Messages.mDbMetaData_invalidCollectionName, collectionName ));
        }