英文:
Accessing $map variable in $cond
问题
以下是您提供的代码的翻译部分：
我有一些存储在MongoDB集合中的数据，看起来像这样：
```javascript
db.test.insertOne(
{ "interactions": [
{
data: "keep",
prompt: "prompt 1"
},
{
other: "keep",
prompt: "prompt 2"
},
{
field: "no prompt"
}
]}
)
我想遍历所有的interactions，并将prompts设置为包含当前prompt值的数组。类似于这样：
{
"interactions": [
{
"data": "keep",
"prompt": "prompt 1",
"prompts": [ "prompt 1" ]
},
{
"other": "keep",
"prompt": "prompt 2",
"prompts": [ "prompt 2" ]
},
{
"field": "no prompt"
}
]
}
我一直在尝试使用带有聚合管道的updateMany()，但出现了一个我不理解的错误。这是我的更新操作：
db.test.updateMany(
{},
[{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
$cond: {
if: { "$$interaction.prompt": { $exists: true } },
then: {
prompts: [ "$$interaction.prompt" ]
},
else: {}
}
}
]
}
}
}
}
}]
)
运行此操作时，我收到错误消息：
无法识别的表达式'$$interaction.prompt'。
运行不带$cond的更新操作可以正常工作：
db.test.updateMany(
{},
[{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
prompts: [ "$$interaction.prompt" ]
}
]
}
}
}
}
}]
)
但在该操作之后，没有prompt的数组元素会具有一个包含null值的数组：
{
"interactions": [
{
"data": "keep",
"prompt": "prompt 1",
"prompts": ["prompt 1"]
},
{
"other": "keep",
"prompt": "prompt 2",
"prompts": ["prompt 2"]
},
{
"field": "no prompt",
"prompts": [null]
}
]
}
我不希望在没有prompt的元素上设置prompts。
那么为什么我无法在$cond中访问$$interaction.prompt？
或者，如果有更好的方法来实现我想要做的事情，请告诉我。
<details>
<summary>英文:</summary>
I have some data in a MongoDB collection that looks something like this:
```javascript
db.test.insertOne(
{ "interactions": [
{
data: "keep",
prompt: "prompt 1"
},
{
other: "keep",
prompt: "prompt 2"
},
{
field: "no prompt"
}
]}
)
I want to iterate over all the interactions, and set prompts to an array containing the current value of prompt. Something like this:
{
"interactions": [
{
"data": "keep",
"prompt": "prompt 1",
"prompts": [ "prompt 1" ]
},
{
"other": "keep",
"prompt": "prompt 2",
"prompts": [ "prompt 2" ]
},
{
"field": "no prompt"
}
]
}
I've been trying to do a updateMany() with an aggregation pipeline, but am getting an error that I don't understand. This is my update:
db.test.updateMany(
{},
[{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
$cond: {
if: { "$$interaction.prompt": { $exists: true } },
then: {
prompts: [ "$$interaction.prompt" ]
},
else: {}
}
}
]
}
}
}
}
}]
)
Running this I get an error:
> Unrecognized expression '$$interaction.prompt'.
Running the update without the $cond works:
db.test.updateMany(
{},
[{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
prompts: [ "$$interaction.prompt" ]
}
]
}
}
}
}
}]
)
but after that operation, the array element that didn't have a prompt has an array with a null value:
{
"interactions": [
{
"data": "keep",
"prompt": "prompt 1",
"prompts": ["prompt 1"]
},
{
"other": "keep",
"prompt": "prompt 2",
"prompts": ["prompt 2"]
},
{
"field": "no prompt",
"prompts": [null]
}
]
}
I don't want prompts set on an element that didn't have prompt.
So why can't I access $$interactions.prompt within the $cond?
Alternatively, if there's a better way to accomplish what I want to do, please let me know.
答案1
得分: 3
在聚合管道中，你不能使用$exists运算符。
而且，你必须以$运算符开头，而不是以变量$$开头。
相反，你需要检查$$interaction.prompt是否既不是undefined也不是null。
英文:
In the aggregation pipeline, you can't use the $exists operator.
And you must start with the $ operator but not with variable $$.
Instead, you check whether $$interaction.prompt is neither undefined nor null.
db.collection.updateMany({},
[
{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
$cond: {
if: {
$not: {
$in: [
"$$interaction.prompt",
[
undefined,
null
]
]
}
},
then: {
prompts: [
"$$interaction.prompt"
]
},
else: {}
}
}
]
}
}
}
}
}
])
答案2
得分: 0
以下是您要翻译的内容：
For some reason, using $not and $in didn't work in my database, although it did in the Playground. After finding an alternative here: https://stackoverflow.com/a/25515046/1303158, my final solution is:
db.collection.update({},
[
{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
$cond: {
if: {
$gt: [
"$$interaction.prompt",
null
]
},
then: {
prompts: [
"$$interaction.prompt"
]
},
else: {}
}
}
]
}
}
}
}
}
],
{
multi: true
})
英文:
For some reason, using $not and $in didn't work in my database, although it did in the Playground. After finding an alternative here: https://stackoverflow.com/a/25515046/1303158, my final solution is:
db.collection.update({},
[
{
$set: {
interactions: {
$map: {
input: "$interactions",
as: "interaction",
in: {
$mergeObjects: [
"$$interaction",
{
$cond: {
if: {
$gt: [
"$$interaction.prompt",
null
]
},
then: {
prompts: [
"$$interaction.prompt"
]
},
else: {}
}
}
]
}
}
}
}
}
],
{
multi: true
})
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