way to update multiple documents with different values

Question

I have the following documents:

[{
  \"_id\":1,
  \"name\":\"john\",
  \"position\":1
},
 {\"_id\":2,
  \"name\":\"bob\",
  \"position\":2
},
 {\"_id\":3,
           


        

Answer 1

Since MongoDB 4.2 update can accept aggregation pipeline as second argument, allowing modification of multiple documents based on their data.

See https://docs.mongodb.com/manual/reference/method/db.collection.update/#modify-a-field-using-the-values-of-the-other-fields-in-the-document

Excerpt from documentation:

Modify a Field Using the Values of the Other Fields in the Document

Create a members collection with the following documents:

db.members.insertMany([
  { "_id" : 1, "member" : "abc123", "status" : "A", "points" : 2, "misc1" : "note to self: confirm status", "misc2" : "Need to activate", "lastUpdate" : ISODate("2019-01-01T00:00:00Z") },
  { "_id" : 2, "member" : "xyz123", "status" : "A", "points" : 60, "misc1" : "reminder: ping me at 100pts", "misc2" : "Some random comment", "lastUpdate" : ISODate("2019-01-01T00:00:00Z") }
])

Assume that instead of separate misc1 and misc2 fields, you want to gather these into a new comments field. The following update operation uses an aggregation pipeline to:

• add the new comments field and set the lastUpdate field.
• remove the misc1 and misc2 fields for all documents in the collection.

db.members.update(
  { },
  [
     { $set: { status: "Modified", comments: [ "$misc1", "$misc2" ], lastUpdate: "$$NOW" } },
     { $unset: [ "misc1", "misc2" ] }
  ],
  { multi: true }
)