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$lt

Definition

$lt

Syntax: { field: { $lt: value } }

$lt selects the documents where the value of the field is less than (i.e. <) the specified value.

For most data types, comparison operators only perform comparisons on fields where the BSON type matches the query value's type. MongoDB supports limited cross-BSON comparison through Type Bracketing.

Examples

The following examples use the inventory collection. Create the collection:

db.inventory.insertMany( [
   {
      item: "nuts", quantity: 30,
      carrier: { name: "Shipit", fee: 3 }
   },
   {
      item: "bolts", quantity: 50,
      carrier: { name: "Shipit", fee: 4 }
   },
   {
      item: "washers", quantity: 10,
      carrier: { name: "Shipit", fee: 1 }
   }
] )

Match Document Fields

Select all documents in the inventory collection where quantity is less than 20:

db.inventory.find( { quantity: { $lt: 20 } } )

Example output:

{
  _id: ObjectId("61ba634dfe687fce2f04241f"),
  item: 'washers',
  quantity: 10,
  carrier: { name: 'Shipit', fee: 1 }
}

Perform an Update Based on Embedded Document Fields

The following example sets the price field based on a $lt comparison against a field in an embedded document.

db.inventory.updateMany( { "carrier.fee": { $lt: 20 } }, { $set: { price: 9.99 } } )

Example output:

{
  _id: ObjectId("61ba634dfe687fce2f04241d"),
  item: 'nuts',
  quantity: 30,
  carrier: { name: 'Shipit', fee: 3 },
  price: 9.99
},
{
  _id: ObjectId("61ba634dfe687fce2f04241e"),
  item: 'bolts',
  quantity: 50,
  carrier: { name: 'Shipit', fee: 4 },
  price: 9.99
},
{
  _id: ObjectId("61ba634dfe687fce2f04241f"),
  item: 'washers',
  quantity: 10,
  carrier: { name: 'Shipit', fee: 1 },
  price: 9.99
}

This updateMany() operation searches for an embedded document, carrier, with a subfield named fee. It sets { price: 9.99 } in each document where fee has a value less than 20.

To set the value of the price field in only the first document where carrier.fee is less than 20, use updateOne().