How to undo/redo operations?

[Sergei Droganov]

Hi,

I'm looking to write schema validation + access control library for sharedb backend.

I want the API to look like this:
harden( backend, schema );

It looks obvious to go this way:

backend.use [ "query", "submit", "after submit" ], (req, next) => validateAccessRights();

backend.use "after submit", (req, next) => validateSchema();

I'm able to validate the operation result against schema at "after submit" hook, but operation is applied despite of error I'm trowing, can I then roll it back somehow or prevent?

[Sergei Droganov]

Here is the problem:
https://github.com/share/sharedb/issues/67

no snapshot on submit or no rollback on after submit. As a result no way to validate the operation result.

[Nate Smith]

You should be using the "apply" and "commit" middleware hooks instead of "submit" and "after submit" for access control. Will write more docs on this later, but apply gives you the snapshot right before the op is applied and commit gives you the snapshot right after the op is applied but before it is committed to the database. You can prevent the submit from completing in any of "submit", "apply", or "commit" by passing an error to next.

An op cannot be rolled back after commit, so you cannot change anything in "after submit".

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[Sergei Droganov]

Hello Nate, this helps, thank you!

[Sivaganeshan B]

Hello, 

interested to know how you have implemented it. could you please share the example?