Set Missing Shard Key Fields

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Example

If you have missing shard key fields, you can set the shard key field to null. If you want to set the missing shard key field to a non-null value, see Change a Document's Shard Key Value.

To perform the update, you can use the following operations on a mongos:

Command	Method	Description
update with `multi: true`	db.collection.updateMany()	Can be used to set the missing key value to `null` only. Can be performed inside or outside a transaction. Can be performed as a retryable write or not. For additional requirements, refer to the specific command/method.
update with `multi: false`	db.collection.replaceOne() db.collection.updateOne()	Can be used to set the missing key value to `null` or any other value. The update to set missing shard key fields must meet one of the following requirements: the filter of the query contains an equality condition on the full shard key in the query the filter of the query contains an exact match on _id the update targets a single shard To set to a non-`null` value, refer to Change a Document's Shard Key Value. For additional requirements, refer to the specific command/method.
findAndModify	db.collection.findOneAndReplace() db.collection.findOneAndUpdate() db.collection.findAndModify()	Can be used to set the missing key value to `null` or any other value. When setting missing shard key fields with a method that explicitly updates only one document, the update must meet one of the following requirements: the filter of the query contains an equality condition on the full shard key in the query the filter of the query contains an exact match on _id the update targets a single shard Missing key values are returned when matching on `null`. To avoid updating a key value that is `null`, include additional query conditions as appropriate. To set to a non-`null` value, refer to Change a Document's Shard Key Value. For additional requirements, refer to the specific command/method.
	`db.collection.bulkWrite()` `Bulk.find.replaceOne()` `Bulk.find.updateOne()` `Bulk.find.update()`	To set to a `null` value, you can specify multiple shard key modifications in the bulk operation. When setting missing shard key fields with a method that explicitly updates only one document, the update must meet one of the following requirements: the filter of the query contains an equality condition on the full shard key in the query the filter of the query contains an exact match on _id the update targets a single shard To set to a non-`null` value, refer to Change a Document's Shard Key Value. For additional requirements, refer to the underlying command/method.

Example

Consider a sales collection which is sharded on the location field. Some documents in the collection have no location field. A missing field is considered the same as a null value for the field. To explicitly set these fields to null, run the following command:

db.sales.updateOne(
  { _id: 12345, location: null },
  { $set: { location: null } }
)

When setting missing shard key fields with db.collection.updateOne() or another method that explicitly updates only one document, the update must meet one of the following requirements:

the filter of the query contains an equality condition on the full shard key in the query
the filter of the query contains an exact match on _id
the update targets a single Shard

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