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Set Missing Shard Key Fields

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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:

CommandMethodDescription
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