Re: [january-dev] question about metadata

[<Peter.Chang@xxxxxxxxxxxxx>]

Hi Scott,

Executive summary: Do not extend IMetadata as it is an old interface; instead extend MetadataType but only to a single level.

Historically we had metadata then extended it repeatedly as a dataset could only hold a single metadata object. Stacking more interfaces becomes a burden for subsequent developers and stuffs metadata handling code full of tedious type checking clauses.

The issue you encountered is hinted at in the MetadataType interface: the implementation(s) of storing metadata does not handle sub-interfaces too well. The tests in MetadataTest demonstrate what can be achieved (by LazyDatasetBase.findMetadataTypeSubInterface).

The recommended way is to have separate metadata interfaces, and add or retrieve them separately.

Regards,
 Peter


-----Original Message-----
From: january-dev-bounces@xxxxxxxxxxx [mailto:january-dev-bounces@xxxxxxxxxxx] On Behalf Of Scott Lewis
Sent: 06 June 2017 16:48
To: january-dev@xxxxxxxxxxx
Subject: [january-dev] question about metadata

Howdy,

We've been using the January metadata APIs, and I have some questions.  
First some code:

We've added new metadata interfaces...e.g.

interface IIdMetadata extends IMetadata {

...

}

And have an implementing class e.g.:

class IdMetadata extends Metadata implements IIdMetadata {

...

}

We add metadata to a dataset:

dataset.addMetadata(new IdMetadata());

Then we access the metadata:

IIdMetadata id = dataset.getFirstMetadata(IIdMetadata.class);

All this works fine.

We have occasions, however, where we would like to be able to do the
following:

(redeclaration of above IdMetadata class):

class IdMetadata extends Metadata implements IIdMetadata, SomeOtherMetadata {

...

}

and then

SomeOtherMetadata som = dataset.getFirstMetadata(SomeOtherMetadata.class);

and have it return a non-null object (the instance that implements both IIdMetadata and SomeOtherMetadata).

In my current tests, this does not work.   The SomeOtherMetadata.class 
query returns null.   My question:   Is this behavior desired/intended?

Thanksinadvance,

Scott


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