docs(documents): add section on setting deeply nested properties, including warning about nullish coalescing assignment #14972
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…luding warning about nullish coalescing assignment Fix #14944
hasezoey
approved these changes
Oct 17, 2024
| // The following does **NOT** work. | ||
| // Do not use the following pattern with Mongoose documents. | ||
| const doc4 = new TestModel(); | ||
| (doc4.nested.subdoc ??= {}).name = 'Charlie Smith'; |
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does this not work because mongoose is cloning on assignment? (i have tried in a node REPL)
ret = (doc4.nested.subdoc ??= {})
ret === doc4.nested.subdoc // eval "false"
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Yes. The problem is the following:
const x = {};
(doc4.nested.subdoc ??= x) === x; // true
doc4.nested.subdoc === x; // falseBasically a.b ??= x evaluates to x, not the value of a.b after the assignment. Which isn't a big deal in most cases, but with Mongoose the distinction matters.
We need to clone because doc4.nested.subdoc needs change tracking. This may be a case where using proxies instead of Object.defineProperty() for change tracking would help.
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Fix #14944
Summary
Add section in the docs about setting deeply nested paths. Clarify that
?.and??are fine, we also support.get()and.set(), but??=comes with caveats.Examples