MongoDB update with condition

Question

I'm trying to update some field in my collection depending on a condition.

I want to set field active to true if the condition is true and to false otherwise

This is update without condition

db.consent.update( {}, //match all {     $set: {         "active": true     } },  {     multi: true, }  ) 

I would like to add a condition to update like this:

db.consent.update( {}, $cond: {     if: {          $eq: ["_id", ObjectId("5714ce0a4514ef3ef68677fd")]      },     then: {         $set: {             "active": true         }     },     else: {         $set: {             "active": false         }     } },  {     multi: true, } 

)

According to https://docs.mongodb.org/manual/reference/operator/update-field/ there is no $cond operator for update.

What are my options here to execute this update as a single command?

Answer 1

Starting Mongo 4.2, db.collection.update() can accept an aggregation pipeline, finally allowing the update/creation of a field based on another field:

// { a: "Hello", b: "World" } // { a: "Olleh", b: "Dlrow" } db.collection.update(   {},   [ { $set: { active: { $eq: [ "$a", "Hello" ] } } } ],   { multi: true } ) // { a: "Hello", b: "World", active: true  } // { a: "Olleh", b: "Dlrow", active: false } 

• The first part {} is the match query, filtering which documents to update (in our case all documents).

• The second part [ { $set: { active: { $eq: [ "$a", "Hello" ] } } } ] is the update aggregation pipeline (note the squared brackets signifying the use of an aggregation pipeline). $set is a new aggregation operator and an alias of $addFields. Then any aggregation operator can be used within the $set stage; in our case a conditional equality check on which depends the value to use for the new active field.

• Don't forget { multi: true }, otherwise only the first matching document will be updated.

Answer 2

You can't.

Mongo doesn't support combining fields, conditionals etc. in the update statement.

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See https://stackoverflow.com/a/56551655/442351 below.