Metadata

Metadata provides a way for actions (Action) to control about how a handler should perform the reading (Reader) and writing (Writer) operations. Therefore, making possible handlers to perform differently per action basis.

This is done by defining Reader & Writer options through the metadata. By doing that the options are passed from the action to the handler during the handler's execution (Handler.runAction).

You can define options by either using option variables or the full option location:

Option var (recommended): Eliminates the need of using convoluted long names to define the options by simply using a variable that represents a full option location:

Example:

class MyAction extends Mebo.Action{

   constructor(){
     super();
     // defining a custom uploadDirectory by using the `$webUploadDirectory` variable,
     // rather than the full option location (`handler.web.readOptions.uploadDirectory`)
     this.setMeta('$webUploadDirectory', '/tmp/customUploadDir');
   }

   async _perform(data){
     // ...
   }

   async _after(err, value){
     // defining a custom header that only affects the web handler
     // this call could be done inside of the _perform method. However, we
     // are defining it inside of the _after to keep _perform as
     // abstract as possible. Since, _after is always called (even during
     // an error) after the execution of the action, it provides a way to
     // hook and define custom metadata related with the result.
     if (!err){
       // defining a custom header by using the `$webHeaders` variable, rather
       // than the full option location (`handler.web.writeOptions.headers`)
       this.setMeta('$webHeaders', {
         someOption: 'foo',
       });
     }
   }
}

Full option location: Uses a convention interpreted by the Handler.metadata to describe where the option is localized:

handler.<HANDLER_NAME>.<OPERATION>Options.<OPTION_NAME>

Example:

class MyAction extends Mebo.Action{
   constructor(){
     super();
     this.setMeta('handler.web.readOptions.uploadDirectory', '/tmp/customUploadDir');
   }

   async _perform(data){
     // ...
   }

   async _after(err, value){

     if (!err){
       // location (not recommended, see option var)
       this.setMeta('handler.web.writeOptions.headers', {
         someOption: 'foo',
       });
     }
   }
}

The complete list of the available option variables can be found bellow, it's separated by handler type. Also, new variables can be assigned through Metadata.registerOptionVar.

Web Variables

Cli Variables