$lt

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Definition定义

$lt

Syntax: 语法：{ field: { $lt: value } }

$lt selects the documents where the value of the field is less than (i.e. <) the specified value.选择field值小于（即<）指定value的文档。

For most data types, comparison operators only perform comparisons on fields where the BSON type matches the query value's type. 对于大多数数据类型，比较运算符仅对BSON类型与查询值类型匹配的字段执行比较。MongoDB supports limited cross-BSON comparison through Type Bracketing.MongoDB通过类型括号支持有限的跨BSON比较。

Examples示例

The following examples use the inventory collection. 以下示例使用inventory集合。Create the collection:创建集合：

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匹配文档字段

Select all documents in the inventory collection where quantity is less than 20:选择inventory集合中quantity小于20的所有文档：

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

Example output:示例输出：

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

Perform an Update Based on Embedded Document Fields基于嵌入式文档字段执行更新

The following example sets the price field based on a $lt comparison against a field in an embedded document.以下示例基于$lt与嵌入文档中的字段的比较设置price字段。

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

Example output:示例输出：

{
  _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. 此updateMany()操作搜索嵌入的文档carrier，其子字段名为fee。It sets { price: 9.99 } in each document where fee has a value less than 20.它在fee值小于20的每个文档中设置{ price: 9.99 }。

To set the value of the price field in only the first document where carrier.fee is less than 20, use updateOne().要仅在carrier.fee小于20的第一个文档中设置price字段的值，请使用updateOne()。

Tip提示
See also: 参阅：
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