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Velo by Wix: Side effect wix-data saving methods

The wix-data methods for saving data has a side effect that I have spent a few hours debugging. In this post, I share how it goes

a picture by motive to serials 'tales from the loop'

We have three methods for manipulation of the database collection that has the same side effect. I found this behavior when it broke my logic in the data hook.

The pasted item is mutating after any of these methods is done:

So, consider the code example where we output to console a new item before and after inserting it into a collection.

import wixData from 'wix-data';

(async () => {
  const item = { title: 'hello' };

  console.log(1, item);

  const result = await wixData.insert('notes', item);

  console.log(2, item);

  console.log(3, result === item);

In the console:

1 {"title":"hello"}

2 {"title":"hello","_createdDate":"2020-11-21T18:34:29.050Z","_updatedDate":"2020-11-21T18:34:29.050Z","_id":"6e616318-ffdb-4954-9529-84c6a63f5393"}

3 true

We can see above what, after inserting a new item, it is mutated and item has new properties. And the insert method returns the same mutated item which have passed into method.

wixData.update() and have also this behavior.

How it affects a code

I have a two collection on the site, a Private (only for admins) and Public (for any one).

In my case, I used a data hook that saves a new item to Private collection, and inside data hook for Private collection I create a new row for Public collection with part of initial data.


export async function Private_afterInsert(item) {
  await wixData.insert('Public', item.publicData);

   * Here I have a mutated item after inserting it into a Public database.

I had a mutated item after inserting it into a Public database, and it created a bug.

For fixing it, I should copy an object before inserting. I use the object spread operator:

// Creates a copy of item
await wixData.insert('Private', { ...item.publicData });

Methods for multiple items

We also have methods that can work with a number of items. Let's consider three of these which use to save data:

We can get to repeat the experiment. These methods accept an array of items.

import wixData from 'wix-data';

(async () => {
  const a = { title: 'a' };
  const b = { title: 'b' };

  console.log(1, a, b);

  const result = await wixData.bulkInsert('notes', [a, b]);

  console.log(2, a, b);

  console.log(3, result);

In the console:

1 {title: "a"} {title: "b"}

2 {title: "a"} {title: "b"}

3 {
  errors: [],
  inserted: 2,
  insertedItemIds: [
  length: 2,
  skipped: 0,
  updated: 0,
  updatedItemIds: [],

Great, bulk methods work differently. They don't mutate the passed items and don't return the mutated items back. The successfully done bulk methods return the Promise<WixDataBulkResult> that contains the info about the changes.


The understanding of how to work the platform is an important thing. If I catch the bugs that grow from a misunderstanding of some of the processes, then I prefer to spend time searching, experiments, and testing it.

When the platform is not a black box for you, this saves more time than you have spent learning it.