$set¶

Set Top-Level Fields设置顶级字段¶

For the document matching the criteria _id equal to 100, the following operation uses the $set operator to update the value of the quantity field, details field, and the tags field.对于匹配条件_id等于100的文档，以下操作使用$set运算符更新quantity字段、details字段和tags字段的值。

db.products.update(
   { _id: 100 },
   { $set:
      {
        quantity: 500,
        details: { model: "14Q3", make: "xyz" },
        tags: [ "coats", "outerwear", "clothing" ]
      }
   }
)

The operation replaces the value of: quantity to 500; the details field to a new embedded document, and the tags field to a new array.该操作将：quantity的值替换为500；将details字段添加到新的嵌入文档，将tags字段添加到新数组。

Set Fields in Embedded Documents在嵌入文档中设置字段¶

To specify a <field> in an embedded document or in an array, use dot notation.若要在嵌入式文档或数组中指定一个<field>，请使用点表示法。

For the document matching the criteria _id equal to 100, the following operation updates the make field in the details document:对于符合条件_id等于100的文档，以下操作将更新详细信息文档中的make字段：

db.products.update(
   { _id: 100 },
   { $set: { "details.make": "zzz" } }
)

Set Elements in Arrays在数组中设置元素¶

To specify a <field> in an embedded document or in an array, use dot notation.若要在嵌入式文档或数组中指定一个<field>，请使用点表示法。

For the document matching the criteria _id equal to 100, the following operation updates the value second element (array index of 1) in the tags field and the rating field in the first element (array index of 0) of the ratings array.对于匹配条件_id等于100的文档，以下操作将更新tags字段中的值的第二个元素（数组索引为1）和ratings数组中第一个元素（数组索引为0）中的rating字段。

db.products.update(
   { _id: 100 },
   { $set:
      {
        "tags.1": "rain gear",
        "ratings.0.rating": 2
      }
   }
)

For additional update operators for arrays, see Array Update Operators.有关阵列的其他更新运算符，请参阅数组更新运算符。