applySnapshot does not call preProcessSnapshot when using types.snapshotProcessor

[khomyakov42]

Bug report

• [v] I've checked documentation and searched for existing issues
• [v] I've made sure my project is based on the latest MST version
• [v] Fork this code sandbox or another minimal reproduction.

Sandbox link or minimal reproduction code
https://codesandbox.io/embed/mobx-state-tree-todolist-1o4pm

Describe the expected behavior
applySnapshot will call preProcessSnapshot and postProcessSnapshot

Describe the observed behavior
applySnapshot called only postProcessSnapshot

[mario-jerkovic]

Any update on this?

[mweststrate]

Sorry, didn't have time personally yet to dive into this. But as the label suggests, feel free to chime in :). A PR with unit tests is already helpful.

[Aryk]

Anybody found a workout around for this?

[jamonholmgren]

Re-opening, as there are issues with #1823 and I reverted it before releasing.

[jcready]

Until this is fixed it should be mentioned in the docs that snapshot preprocessing is fundamentally broken and shouldn't be used.

[evinosheaforward]

I started to take a look at this, but I haven't figured it out.
I'm using the test from @Jarrku:

  test("applySnapshot runs preprocessors before applying - simple", () => {
    const M = types.snapshotProcessor(types.model({ x: types.number }), {
      preProcessor(snapshot: { x: string }) {
        return { x: Number(snapshot.x) }
      },
      postProcessor(snapshot) {
        return { x: String(snapshot.x) }
      }
    })
    const m = M.create({ x: "1" })
    expect(() => applySnapshot(m, { x: "2" })).not.toThrow()
  })

when applySnapshot is called, applySnapshotPreProcessor is called (in src/types/complex-types/model.ts)
however, when it is, this.preProcessor is not set / is undefined.

It seems that when SnapshotProcessor is constructed, the _subtype is not given .preProcessor and .postProcessor attributes.
When I tried to set them I got type errors.
I haven't been able to understand the inheritance model to the level of understanding how to fix the issue.

[coolsoftwaretyler]

Thanks @evinosheaforward - I know you and I are talking offline about this but wanted to acknowledge your comment publicly so folks know we are collaborating on the fix together.

When you get a chance, if you have more specific questions about the details, ask 'em here so we can sort of document-in-public!