November 2021
Intermediate to advanced
410 pages
12h 1m
Chinese
Content preview from MongoDB权威指南（第3版）
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创建、更新和删除文档
｜
35
> db.strcounts.update({}, {"$inc" : {"count" : 1}})
WriteResult({
"nMatched" : 0,
"nUpserted" : 0,
"nModified" : 0,
"writeError" : {
"code" : 16837,
"errmsg" : "Cannot apply $inc to a value of non-numeric type.
{_id: ObjectId('5726c0d36855a935cb57a659')} has the field 'count' of
non-numeric type String"
}
})
同样，
"$inc"
键的值必须为数字类型。不能使用字符串、数组或者其他非数字类型的值。
否则会提示错误信息：“
Modifier
"$inc"
allowed for numbers only
”。如果需要修改其他类型
的值，可以使用
"$set"
或者下面要讲到的数组运算符。
3.
数组运算符
MongoDB
中
有一大类更新运算符用于操作数组。数组是常用且功能强大的数据结构：它
们不仅是可以通过索引进行引用的列表，而且可以作为集合来使用。
添加元素
。
如果数组已存在，
"$push"
就会将元素添加到数组末尾；如果数组不存在，
则会创建一个新的数组。假设我们要存储博客文章，并希望添加一个用于保存数组的
"comments"
键。可以向还不存在的
"comments" ...
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