Helper module for generating a sequence of MongoDB document update operations that will transform a document in line with an RFC6902 JSON Patch document. Builds on top of the https://www.npmjs.com/package/rfc6902 module, and produces update operation documents that should work with the standard https://www.npmjs.com/package/mongodb driver.

Usage

NB: the following examples assume you are using the standard mongodb driver, setup for which is not included here.

import { updatesForPatch } from 'rfc6902-mongodb';

const exampleDocument = {
    "biscuits": [
        { "name": "Digestive" },
        { "name": "Choco Leibniz" }
    ]
}

const examplePatch = [
    { "op": "add", "path": "/biscuits/1", "value": { "name": "Ginger Nut" } },
    { "op": "copy", "from": "/biscuits/0", "path": "/best_biscuit" },
    { "op": "remove", "path": "/biscuits" }
];

const insertResult = await collection.insertOne(exampleDocument);
const originalDocument = await collection.findOne({ _id: insertResult.insertedId }); // equivalent to exampleDocument
const updates = updatesForPatch(examplePatch, originalDocument);

// Apply each update in order
for await (const update of updates) {
    await collection.updateOne({ _id: insertResult.insertedId }, update);
}

Caveats

The update list produced by the module presumes that the original document provided is an accurate copy of what is in the MongoDB collection. If the collection document differs, or if other updates are made to the document in between the updates returned by the module, then the final document will likely not be correct. It is the responsibility of the caller to handle any locking of documents or other concurrency safety logic, this module does not handle making atomic updates from a potentially complex patch document.

Some degree of optimisation is performed to produce a smaller set of operations. Sometimes multiple patch operations can be easily and safely combined into a single DB update operation, for example when writing new values into unrelated fields. Other patch operations like remove or operations on arrays can affect subsequent operations, by changing the values referred to by operation paths. Unless it is unambiguously safe to coalesce operations together, this implementation will err on the side of correctness: more distinct operations but that are guaranteed to produce the correct final result.

Unsupported patch operations

• While JSON Patches can be applied to arrays as well as objects, MongoDB documents can only be documents. If the original/target document is not an object, the module will refuse to create an update list (throwing an Error object).
• Similarly, by specifying the empty path, JSON patches can describe replacing the document with a value or an array (as these are still valid JSON documents). This is not allowed and will cause an Error to be thrown.
• Patches may also describe replacing the entire document with a new document by specifying the empty path. However in MongoDB, this would require a replaceOne operation, and the expectation is that the returned array describes parameters for calls to updateOne. For API simplicity, the module will throw an Error rather than try to handle this case.
• Patch operations that would result in empty keys (trailing slashes on the path) are supported in JSON, but not well supported in MongoDB; the module will throw an Error if asked to generate updates for such patches.
• Patch operations that contain problematic MongoDB characters in the document path or sub-documents being inserted (e.g. leading $, . and \0 characters) will throw an Error.