Bulkupdate problems

Hi experts,
I am executing the following code to update some specific fields in the database.
As you can see in the picture the first 2 rows have been filled with the references (Adler, Dietrich) as expected but the bulkupdate also did overwrite the “Title” and “Anfang” column. (There was text before)

I was expecting that within the _id row only the field “lyra” or “omego” will be updated rest stays the same!?

Any idea how to accomplish this?
Thanks guys!

export function button12_click(event) {
let toUpdate1 = {
"_id":          "3d8bc591-6621-4e4f-a61f-9ef3723576e6",
"omego":        "554b6375-9015-4127-b9e1-2303c12926ee",
};
let toUpdate2 = {
"_id":          "c1e69eff-678c-4684-a4aa-dde451dd65bb",
"lyra":        "554b6375-9015-4127-b9e1-2303c12926ee",
};
wixData.bulkUpdate("Gruppenkalender", [toUpdate1, toUpdate2])
.then( (results) => {
let inserted = results.inserted; // 0
let insertedIds = results.insertedItemIds; // []
let updated = results.updated; // 2
let skipped = results.skipped; // 0
let errors = results.errors; // []
console.log(results)
} )
.catch( (err) => {
let errorMsg = err;
} );
}

Fetch the data you’re changing first, modify the columns you’re updating and send the complete rows to bulkUpdate.

Thanks for your quick answer @Lee
I agree to your solution but it doesn‘t work for me, since I might update a second field in the same raw within the bulkupdate array.
It worked already some month ago as I remember. What has changed, or am I wrong here?

Hello. You can use hooks and there decide what field should be updated.
Also if you expect that some of the items will have same _id, then you can just transform them into one element before saving to collection.

How you do this in the hook before update. it always updates all fields.
I tried to add :
if ( ! item . uniqueField ) {
return item
}
also didn’t work.
any suggestions please?