Field Names with Periods

Insert a Field Name with a Period

To insert a document that contains a field name with a period, put the field name in quotes.

The following command inserts a document that contains a field name price.usd:

db.inventory.insertOne(
   {
      "item" : "sweatshirt",
      "price.usd": 45.99,
      "quantity": 20
   }
)

Query a Field that has a Period

To query for a field that has a period, use the $getField operator.

The following query returns documents where the price.usd field is greater than 40:

db.inventory.find(
   {
      $expr:
         {
            $gt: [ { $getField: "price.usd" }, 40 ]
         }
   }
)

[
   {
      _id: ObjectId("66145f9bcb1d4abffd2f1b50"),
      item: 'sweatshirt',
      'price.usd': 45.99,
      quantity: 20
   }
]

If you don't use $getField, MongoDB treats the field name with a period as an embedded object. For example, the following query matches documents where a usd field inside of a price field is greater than 40:

db.inventory.find( {
   "price.usd": { $gt: 40 }
} )

The preceding query would match this document:

{
   "item" : "sweatshirt",
   "price": {
      "usd": 45.99
   },
   "quantity": 20
}

Update a Field that has a Period

To update a field that has a period, use an aggregation pipeline with the $setField operator.

The following operation sets the price.usd field to 29.99:

db.inventory.updateOne(
   { "item": "sweatshirt" },
   [
      {
         $replaceWith: {
            $setField: {
               field: "price.usd",
               input: "$$ROOT",
               value: 29.99
            }
         }
      }
   ]
)

If you don't use $setField, MongoDB treats the field name with a period as an embedded object. For example, the following operation does not update the existing price.usd field, and instead inserts a new field usd, embedded inside of a price field:

db.inventory.updateOne(
   { "item": "sweatshirt" },
   { $set: { "price.usd": 29.99 } }
)

Resulting document:

[
   {
      _id: ObjectId("66145f9bcb1d4abffd2f1b50"),
      item: 'sweatshirt',
      'price.usd': 45.99
      quantity: 20,
      price: { usd: 29.99 }
   }
]

For more examples of updates with aggregation pipelines, see Updates with Aggregation Pipeline.

Learn More

• $getField

• $setField

• $literal

• Dollar-Prefixed Field Names