Remove document's content from ModelDB

[hbcarlos]

Follows #11434

I'll be updating this comment until we find the definitive API

Problem

Currently, we have the document's content triplicated in the editor, ModelDB and YJS. I.e., the same content is mirrored in different data structures. This means that every time one of the models changes, we must update all other models to keep them in sync. This approach is very complex and prone to bugs. As commented several times, we need to remove the content from ModelDB and use only the shared models to manipulate it. This will allow us to simplify the existing code. For extension authors, this means that the API will change.

Proposed Solution

The idea is to open multiple PRs to remove attributes from ModelDB and keep them only in the shared models. Some of the changes are:

Remove document's content:

• More information in its corresponding PR Remove source from modelDB #11601

Remove document's metadata:

• PR: none yet
• API changes:
  • Document's metadata are stored in ModelDB as an IObservableJSON named metadata. We want to remove this attribute from ModelDB to use its equivalent from the shared model:
    • Notebook:
      

      jupyterlab/packages/notebook/src/model.ts

      Line 108 in 014091f

      const metadata = this.modelDB.createMap('metadata');

      
      

      jupyterlab/packages/shared-models/src/ymodels.ts

      Line 472 in 014091f

      public ymeta: Y.Map<any> = this.ydoc.getMap('meta');

    • Cells:
      

      jupyterlab/packages/cells/src/model.ts

      Lines 185 to 187 in 014091f

      	const observableMetadata = this.modelDB.createMap('metadata');
      	observableMetadata.changed.connect(this.onModelDBMetadataChange, this);
      	observableMetadata.changed.connect(this.onGenericChange, this);

      
      

      jupyterlab/packages/shared-models/src/ymodels.ts

      Line 625 in 014091f

      ymodel.set('metadata', {});

  • Regarding the models the change would be readonly metadata: IObservableJSON -> readonly metadata: nbformat.INotebookMetadata
    • Notebook:
      

      jupyterlab/packages/notebook/src/model.ts

      Line 65 in 014091f

      readonly metadata: IObservableJSON;

      
      

      jupyterlab/packages/notebook/src/model.ts

      Lines 165 to 167 in 014091f

      	get metadata(): IObservableJSON {
      	return this.modelDB.get('metadata') as IObservableJSON;
      	}

    • Cells:
      

      jupyterlab/packages/cells/src/model.ts

      Line 65 in 014091f

      readonly metadata: IObservableJSON;

      
      

      jupyterlab/packages/cells/src/model.ts

      Lines 251 to 253 in 014091f

      	get metadata(): IObservableJSON {
      	return this.modelDB.get('metadata') as IObservableJSON;
      	}

  • Changing the metadata property is a huge change because at the moment the IObservableJSON extends from IObservableMap, this means that we can change and listen to changes in specific attributes of the metadata. With the new implementation, this won't be possible since in the shared models we need to replace the whole metadata object every time we want to add|remove|update an attribute. The reason is to avoid inconsistent states of the metadata, for example when one client is changing the execution count while another is switching the type of the cell to a markdown. The metadata could end up being a markdown cell with the attribute executionCount.

Remove cell's outputs:

• PR: none yet
• API changes:
  • Not sure yet.
  • The problem with the outputs is that they are stored in the view and the shared model. Maybe it is better to have the state stored in the shared model and render them every time.