我的产品文档是这样的:
{
"_id": {
"$oid": "60999af1160b0eebed51f203"
},
"name": "Olive Skin care On1",
"business": {
"$oid": "609fa1d25adc157a33c59098"
},
"ratings": [{
"_id": {
"$oid": "60bdb541d6212ec44e62273c"
},
"user": {
"$oid": "5fdce4bd75dbe4864fcd5001"
},
"rating": 5
}]
}
我有这个 mongoose 查询来获取产品详细信息以及产品评级。一些产品有评级字段,而另一些则没有。当我按此处所示进行查询时,它会按预期返回响应并计算出平均评分。响应如下:
[
{
"_id": "609a657f2bf43c290fb22df8",
"name": "Olive babay Oil",
"business": "6079ed084d9ab0c3171317ea",
"averageRating": 5
}
]
这是查询:
const productArray = await Product.aggregate([
{
$match: {
_id: mongooseProductId,
},
},
{ $unwind: "$ratings" },
{
$project: {
averageRating: { $avg: "$ratings.rating" },
name: 1,
business: 1,
},
},
]);
但是,如果通过删除 ratings 字段修改了上面的相同产品,则下面的查询将返回一个空数组。 如何编写查询以确保 ratings 字段是否存在,如果满足匹配条件,我不会得到空数组。
这意味着当我的产品文档中不存在 ratings 字段时,我可以获得这样的预期响应:
[
{
"_id": "609a657f2bf43c290fb22df8",
"name": "Olive babay Oil",
"business": "6079ed084d9ab0c3171317ea",
"averageRating": null
}
]
当评级字段存在时:
[
{
"_id": "609a657f2bf43c290fb22df8",
"name": "Olive babay Oil",
"business": "6079ed084d9ab0c3171317ea",
"averageRating": 5
}
]
答案 0 :(得分:0)
基于@turivishal 的评论。下面的查询解决了这个问题。
const productArray = await Product.aggregate([
{
$match: {
_id: mongooseProductId,
},
},
{ $unwind:{ path: "$ratings", preserveNullAndEmptyArrays: true } },
{
$project: {
averageRating: { $avg: "$ratings.rating" },
name: 1,
business: 1,
},
},
]);