$in
Syntax: { field: { $in: [<value1>, <value2>, ... <valueN> ] } }
$in selects the documents where the field value equals any value in the specified array (e.g. <value1>, <value2>, etc.)
Consider the following example:
db.inventory.find( { qty: { $in: [ 5, 15 ] } } )
This query selects all documents in the inventory collection where the qty field value is either 5 or 15. Although you can express this query using the [$or](or.html#_S_or) operator, choose the $in operator rather than the [$or](or.html#_S_or) operator when performing equality checks on the same field.
If the field holds an array, then the $in operator selects the documents whose field holds an array that contains at least one element that matches a value in the specified array (e.g. <value1>, <value2>, etc.)
Consider the following example:
db.inventory.update( { tags: { $in: ["appliances", "school"] } }, { $set: { sale:true } } )
This [update()](db.collection.update.html#db.collection.update) operation will set the sale field value in the inventory collection where the tags field holds an array with at least one element matching an element in the array ["appliances", "school"].
也可以參考
[find()](db.collection.find.html#db.collection.find), [update()](db.collection.update.html#db.collection.update), [$or](or.html#_S_or), [$set](set.html#_S_set).
以上是 MongoDB中文文檔 給出的解釋和語法
MongoDB sort() 方法
在 MongoDB 中使用 sort() 方法對數據進行排序，sort() 方法可以通過參數指定排序的字段，並使用 1 和 -1 來指定排序的方式，其中 1 爲升序排列，而 -1 是用於降序排列。
語法
sort()方法基本語法如下所示：
>db.COLLECTION_NAME.find().sort({KEY:1})例如：db.getCollection('mongo_test').find().sort({_id:-1})
例如：查詢mongo_test集合 id在170735,19786503,170732,170764,19786435中的數據，並按id降序排列
db.getCollection('mongo_test').find({_id:{$in: [170735,19786503,170732,170764,19786435]}}).sort({_id:-1})
