MongoDB 找到最接近的匹配项

Question

我想知道是否可以通过最接近的匹配访问 MongoDB 中的文档。例如我的搜索查询总是包含:
名称
国家
城市

制定了以下规则:
1. name 必须始终匹配
2. 如果存在country或city，country具有更高的优先级
3. 如果 country 或 city 不匹配，仅考虑此文档，如果它们具有默认值(例如，对于 String: "")

示例查询:
名称 = "测试"
国家 = "美国"
城市 = "西雅图"

文件:

db.stuff.insert([
{
    name:"Test",
    country:"",
    city:"Seattle"
},{
    name:"Test3",
    country:"USA",
    city:"Seattle"
},{
    name:"Test",
    country:"USA",
    city:""
},{
    name:"Test",
    country:"Germany",
    city:"Seattle"
},{
    name:"Test",
    country:"USA",
    city:"Washington"
}
])

它应该返回第三个文档

谢谢!

Answer 1

考虑到不确定的要求和相互矛盾的更新，答案更像是一个解决“是否可能”部分的指南。

应调整示例以满足预期。

db.stuff.aggregate([
    {$match: {name: "Test"}}, // <== the fields that should always match
    {$facet: {
        matchedBoth: [
            {$match: {country: "USA", city: "Seattle"}},  // <== bull's-eye
            {$addFields: {weight: 10}}                    // <== 10 stones
        ],
        matchedCity: [
            {$match: {country: "", city: "Seattle"}},   // <== the $match may need to be improved, see below 
            {$addFields: {weight: 5}}            
        ],
        matchedCountry: [
            {$match: {country: "USA", city: ""}},
            {$addFields: {weight: 0}}                  // <== weightless, yet still a match
        ]
        // add more rules here, if needed
    }},
    // get them together. Should list all rules from above  
    {$project: {doc: {$concatArrays: ["$matchedBoth", "$matchedCity", "$matchedCountry"]}}},
    {$unwind: "$doc"},              // <== split them apart
    {$sort: {"doc.weight": -1}},    // <== and order by weight, desc
    // reshape to retrieve documents in its original format 
    {$project: {_id: "$doc._id", name: "$doc.name", country: "$doc.country", city: "$doc.city"}}
]);

问题中解释最少的部分会影响我们构建方面的方式。例如

{$match: {country: "", city: "西雅图"}}

匹配国家/地区明确存在且为空字符串的所有文档。

很有可能是

{$match: {country: {$ne: "USA"}, city: "Seattle"}}

获取所有具有匹配名称和城市以及任何国家/没有国家的文件，甚至

{$match: {$and: [{$or: [{country: null}, {country: ""}]}, {city: "Seattle"}]}}

等等