node.js - Node + Mongodb + 排序嵌套数组

Question

我正在将 Node 与 mongodb 结合使用。我尝试对嵌套数组进行排序。

monogodb 中的示例 json。

{
    "items": [
        {
            "name": "A",
            "order": 3
        }, {
            "name": "B",
            "order": 2
        }, {
            "name": "C",
            "order": 1
        }, {
            "name": "D",
            "order": 4
        }
    ],
    "name": "Test",
        "_id" : 01245678913
}
{
    "items": [
        {
            "name": "A",
            "order": 3
        }, {
            "name": "B",
            "order": 2
        }, {
            "name": "C",
            "order": 1
        }, {
            "name": "D",
            "order": 4
        }
    ],
    "name": "Test",
        "_id" : 098765432134
}

我期望结果应该根据顺序显示。 items.order

这里可以传递ID。如果获取 Id 意味着显示相应 Id 的结果。否则需要显示所有列表。

我附上了我的 Node 代码:

router.post('/get', function(req, res, next) {

        var results = {
            resp : {},
            id : null,
            query : {}
        };

        if (!( typeof req.body['id'] === 'undefined' || req.body['id'] === null )) {
            results.id = req.body['id'];
        }

        Q(results).then(function(results) {
            var deferred = Q.defer();
            var collection = mongoUtil.list;
            if (results.id != null) {
                results.query._id = ObjectId(results.id);
            }


            collection.find(results.query).toArray(function(err, lists) {

                if (!err && lists.length > 0) {
                    results.resp.lists = lists;
                    deferred.resolve(results);
                } else {

                    results.resp.message = 'No List';
                    results.resp.debug = err;
                    deferred.reject(results);
                }
            });
            return deferred.promise;
        }).then(function(results) {
            results.resp.message = 'Result found';
            results.resp.status = 'Success';
            res.send(results.resp);
        }).fail(function(results) {
            results.resp.status = 'Error';
            res.send(results.resp);
        });

    });

我发现他们使用聚合函数的例子很少。

collection.aggregate([
  {$unwind: "$answers"}, 
  {$sort: {"item.order":1}}, 
  {$group: {_id:"$_id", answers: {$push:"$answers"}}}
]);

这里有点困惑。

Answer 1

聚合操作处理数据记录并返回计算结果。聚合操作将来自多个文档的值分组在一起，并且可以对分组数据执行各种操作以返回单个结果。

试试这个-

collection.aggregate([
  { $unwind: "$items" },
  { $sort: { "items.order": 1 } },
  { $group: { _id: "$_id", items: { $push: "$items" } } }
]);

db.collection.aggregate(pipeline, options):- Calculates aggregate values for the data in a collection.

Pipeline $unwind (aggregation) stage:- Deconstructs an array field from the input documents to output a document for each element. Each output document is the input document with the value of the array field replaced by the element.

Examples-

Consider an inventory items with the following document:

{ "_id" : 1, "item" : "ABC1", sizes: [ "S", "M", "L"] }

以下聚合使用 $unwind 阶段输出文档 对于尺寸数组中的每个元素:

db.items.aggregate( [ { $unwind : "$sizes" } ] )

The operation returns the following results:

{ "_id" : 1, "item" : "ABC1", "sizes" : "S" } { "_id" : 1, "item" :
"ABC1", "sizes" : "M" } { "_id" : 1, "item" : "ABC1", "sizes" : "L" }

管道 $sort(聚合)阶段:- 对所有输入文档进行排序并 按排序顺序将它们返回到管道。

$sort 阶段具有以下原型(prototype)形式:

{ $sort: { <field1>: <sort order>, <field2>: <sort order> ... } }

Examples-

For the field or fields to sort by, set the sort order to 1 or -1 to specify an ascending or descending sort respectively, as in the following example:

db.users.aggregate( [
{ $sort : { age : -1, posts: 1 } } ] )

流水线 $group(聚合)阶段:- 按某些方式对文档进行分组 指定表达式并输出到下一阶段的每个文档 不同的分组。输出文档包含一个 _id 字段，该字段 包含按键不同的组。 $group 不对其输出进行排序 文档。

$group阶段的原型(prototype)形式如下:

{ $group: { _id: <expression>, <field1>: { <accumulator1> :
<expression1> }, ... } }

Accumulator $push:- Returns an array of all values that result from applying an expression to each document in a group of documents that share the same group by key.

$push has the following syntax:

{ $push: <expression> }

$push is only available in the $group stage.

有关更多引用，请参阅此链接 - https://docs.mongodb.com/manual/reference/method/db.collection.aggregate/