Packages Usage Example

The Schema Browser in the following example contains application schemas extending down the DemoCompanySchema branch and a RootSchema subschema called LoggingPackageSchema, which provides log file services we would like to be able to use from our application schemas.

To use the log file services in LoggingPackageSchema in this hierarchy without using a package, we would have to take one of the following actions.

Insert LoggingPackageSchema into the application schema hierarchy above the first schema in which we want to use the services. This can encourage top-heavy schema hierarchies.
Make use of global instance visibility and indirect methods (for example, getSchema, getClass, getPropertyValue, sendMsg, and so on) to access LoggingPackageSchema entities across schemas. This is a commonly implemented approach but the use of meta or indirect methods is more complicated and generally not type-safe at compile time.

By using a package, the LoggingPackageSchema facilities can be seamlessly and type-safely used by any other schema. For the purposes of this example, imagine that LoggingPackageSchema contains the LogManager, Log, and LogTagDict classes shown in the following schema file.

LogManager completeDefinition
    (
    referenceDefinitions
        allLogs:        LogTagDict   explicitInverse, subId = 1, number = 1;

    jadeMethodDefinitions
        create() updating, number = 1001;
        createLog(
            logTag: String;
            appTag: String;
            fileName: String): Log number = 1005;
        delete() updating, number = 1002;
        deleteLog(log: Log io) number = 1006;
        finalize() number = 1003;
        initialize() number = 1004;
    )

Log completeDefinition
    (
    attributeDefinitions
        appTag:                        String[52] number = 2;
        fileName:                      String[258] number = 3;
        fred:                          Character protected, number = 5;
        logTag:                        String[52] number = 1;
    referenceDefinitions
        myLogManager:      LogManager   explicitEmbeddedInverse, number = 4;

    jadeMethodDefinitions
        close() number = 1001;
        create() updating, number = 1003;
        delete() updating, number = 1004;
        log(txt: String) number = 1005;
        open() number = 1002;
    )

LogTagDict completeDefinition
    (
    )

memberKeyDefinitions
    LogTagDict completeDefinition
    (
        appTag;
        logTag;
    )

exportedPackageDefinitions
    Logging
    (
    exportedClassDefinitions
    Log
        (
        exportedPropertyDefinitions
            appTag;
            fileName;
            logTag;
        exportedMethodDefinitions
            close;
            log;
            open;
        )
    LogManager
        (
        exportedPropertyDefinitions
            allLogs;
        exportedMethodDefinitions
            createLog;
            deleteLog;
        )
    LogTagDict
        (
        )
    )

referenceDefinitions
        myExceptionLog:          Logging::Log  protected, number = 2;
        myLogManager:            Logging::LogManager  protected, number = 1;
        myMsgLog:                Logging::Log  protected, number = 4;
        myPollingLog:            Logging::Log  protected, number = 3;

appInit
{
appInit() updating;
begin
    create self.myLogManager transient;
    self.myExceptionLog := self.myLogManager.createLog('DEMO',
        'ExLog', 'c:\temp\ex.log');
    self.myPollingLog := self.myLogManager.createLog('DEMO',
        'PollLog', 'c:\temp\poll.log');
    self.myMsgLog := self.myLogManager.createLog('DEMO',
        'MsgLog', 'c:\temp\msg.log');
    self.myExceptionLog.open;
    self.myPollingLog.open;
    self.myMsgLog.open;
    self.myMsgLog.log('Opened logs ' &
        self.myExceptionLog.fileName & ' , ' &
        self.myPollingLog.fileName & ' , ' & self.myMsgLog.fileName);
end;
}

appFini
{
appFini() updating;
begin
    self.myLogManager.deleteLog(self.myExceptionLog);
    self.myLogManager.deleteLog(self.myPollingLog);
    self.myLogManager.deleteLog(self.myMsgLog);
    delete self.myLogManager;
end;
}

appFini
{
appFini() updating;
begin
    self.myLogManager.deleteAllLogs;
    delete self.myLogManager;
end;
}

Although LoggingPackageSchema can also contain numerous implementation classes, we are not concerned with these in this packages usage example.