javascript - Mongodb 通过 id 在数组中找到一个对象

Question

我试图通过用户 ID 和选定的字段和项目找到我的数据库文档的特定条目。我希望返回项目对象。这是文档结构:

{
"_id": ObjectId("58edfea4b27fd0547375eeb4"),
"user_id": ObjectId("58d2dd4c8207c28149dbc748"),
"calories": 2000,
"date": 20170312,
"snacks": [ ],
"dinner": [
 {
  "nutrients": {
    "protein": "11.6",
    "carbs": "29.4",
    "fat": "7.9"
  },
  "servings": "75",
  "calories": 750,
  "name": "Meat feast stone baked pizza"
}, 
{
  "nutrients": {
    "protein": "6.8",
    "carbs": "54",
    "fat": "30.6"
  },
  "servings": "25",
  "calories": 550,
  "name": "Mc Coy's Cheddar and onion"
}],
"lunch": [],
"breakfast": [],
}

到目前为止，我所做的是获取用户 ID、日期，然后是要搜索的选定餐点和项目。我返回的是整个膳食数组，但我只想要返回食品对象。

user_food.findOne({user_id : req.session.user_id, date: today},{'dinner': 'Meat feast stone baked pizza'},function(err, item){
        if(err){
            console.log("something went wrong: " + err);
            return res.status(500).send(err);
        }
        else{
            console.log(item);
            return res.status(200).send(item);
        }
    });

我得到的返回是这样的:

"dinner": [
{
  "nutrients": {
    "protein": "11.6",
    "carbs": "29.4",
    "fat": "7.9"
  },
  "servings": "75",
  "calories": 750,
  "name": "Meat feast stone baked pizza"
}, 
{
  "nutrients": {
    "protein": "6.8",
    "carbs": "54",
    "fat": "30.6"
  },
  "servings": "25",
  "calories": 550,
  "name": "Mc Coy's Cheddar and onion"
}]

我想要的只是:

    {
  "nutrients": {
    "protein": "11.6",
    "carbs": "29.4",
    "fat": "7.9"
  },
  "servings": "75",
  "calories": 750,
  "name": "Meat feast stone baked pizza"
}

Answer 1

试试这个:

user_food.
findOne({
        user_id : req.session.user_id, 
        date: today,
        'dinner.name': 'Meat feast stone baked pizza'
    },{
        'dinner.$' : 1
},function(err, item){
    ....
});

dinner.$ 将只返回符合条件的晚餐项目，即 dinner.name : Meat feast stone baked pizza。

了解 $(positional) operator了解有关从查询结果中限制数组内容并返回与查询文档匹配的元素的更多信息。