如何获取数组嵌入数组猫鼬的大小？
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【中文标题】如何获取数组嵌入数组猫鼬的大小？【英文标题】：How to get size of array embedded array mongoose? 【发布时间】：2020-01-02 10:01:10 【问题描述】：我有一个类别集合，我想通过一些选项通过 id 获取类别。这是数据库中集合的结构。
[
"_id": "5d67296bf35b984e74486924",
"name": "Dinrk",
"images": [],
"recipes": [
"name": "Coffee",
"time": 20,
"img": "https://google.com/image-example.jpg",
"des": "This is description",
"serving": 2,
"components": [
"name": "Dink 1",
"quantity": "1"
,
"name": "Dink 2",
"quantity": "1"
,
"name": "Dink 2",
"quantity": "1"
],
"cook_steps": [
"des": "This is description",
"pictures": []
,
"des": "This is description",
"pictures": []
]
,
"name": "Coffee",
"time": 20,
"img": "https://google.com/image-example.jpg",
"des": "This is description",
"serving": 2,
"components": [
"name": "Dink 1",
"quantity": "1"
,
"name": "Dink 2",
"quantity": "1"
],
"cook_steps": [
"des": "This is description",
"pictures": []
,
"des": "This is description",
"pictures": []
]
]
,
"_id": "5d67296bf35b984e74486435555",
"name": "Cake",
"images": [],
"recipes": [
"name": "Cake",
"time": 20,
"img": "https://google.com/image-example.jpg",
"des": "This is description",
"serving": 2,
"components": [
"name": "Cake 1",
"quantity": "1"
,
"name": "Cake 2",
"quantity": "1"
,
"name": "Cake 2",
"quantity": "1"
],
"cook_steps": [
"des": "This is description",
"pictures": []
,
"des": "This is description",
"pictures": []
]
,
"name": "Coffee",
"time": 20,
"img": "https://google.com/image-example.jpg",
"des": "This is description",
"serving": 2,
"components": [
"name": "Cake 1",
"quantity": "1"
],
"cook_steps": [
"des": "This is description",
"pictures": []
,
"des": "This is description",
"pictures": []
]
]
]
这是我尝试 categoryId = "5d67296bf35b984e74486924" 的代码
Category.aggregate([
$match: '_id': categoryId
,
$unwind: '$recipes'
,
$project:
'total_components': '$size': '$recipes.components',
'total_cook_steps': '$size': '$recipes.cook_steps'
]).then(function(data)
, function(err)
)
预期结果是
"_id": "5d67296bf35b984e74486924",
"name": "Dinrk",
"images": [],
"recipes": [
"name": "Coffee",
"time": 20,
"img": "https://google.com/image-example.jpg",
"des": "This is description",
"serving": 2,
"total_components": 3,
"total_cook_steps": 2
,
"name": "Coffee",
"time": 20,
"img": "https://google.com/image-example.jpg",
"des": "This is description",
"serving": 2,
"total_components": 2,
"total_cook_steps": 2
]
但是当我在我的代码上面运行时，结果是 []。
如果你理解我的问题，请帮助我。我搜索了很多，但没有找到解决方案。所以想问问大家。非常感谢。
【问题讨论】：
categoryId 的类型必须是 ObjectId 而不是字符串。 ***.com/questions/16310598/…
【参考方案1】：
你的查询没有给你想要的结果，因为 Mongoose does not auto-cast the 24 char hex string to ObjectId in its aggregate pipeline 因为 $project 和 $group 可以以令人惊讶的方式更改架构，因此很难推断应该是 ObjectId。
您需要手动转换categoryId
使用mongoose.Types.ObjectId 方法将字符串转换为ObjectId。
在 $map 运算符而不是 $unwind 中计算新字段，因为这允许您使用更少的管道步骤进行聚合操作
Category.aggregate([
'$match': '_id': mongoose.Types.ObjectId(categoryId) ,
'$addFields':
'recipes':
'$map':
'input': '$recipes',
'in':
'name': '$$this.name',
'time': '$$this.time',
'img': '$$this.img',
'des': '$$this.des',
'serving': '$$this.serving',
'total_components': '$size': '$$this.components' ,
'total_cook_steps': '$size': '$$this.cook_steps'
]).then(function(data)
, function(err)
)
【讨论】：
太棒了，它成功了。太感谢了。我真的很感激！以上是关于如何获取数组嵌入数组猫鼬的大小？的主要内容，如果未能解决你的问题，请参考以下文章