MongoDB find closest match - mongodb

Question

I'm wondering if it is possible to access a document in MongoDB via closest match.
e.g. my search query always contains:
name
country
city
Following rules are in place:
1. name always has to match
2. if either country or city is present, country has a higher priority
3. if country or city does not match only consider this document, if they have the default value (e.g. for String: "")
example Query:
name = "Test"
country = "USA"
city = "Seattle"
Documents:
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"
}
])
It should return the 3rd document
thanks!

Answer 1

Considering uncertain requirements and contradicting updates, the answer is rather a guideline addressing the "Is it possible at all" part.
The example should be adjusted to meet expectation.
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: "$doc.city"}}
]);
The least explained part of the question affect how we build up facets. e.g.
{$match: {country: "", city: "Seattle"}}
matches all documents where country explicitly present and is an empty string.
It very well might be
{$match: {country: {$ne: "USA"}, city: "Seattle"}}
to get all documents with matching name and city and any country/no country, or even
{$match: {$and: [{$or: [{country: null}, {country: ""}]}, {city: "Seattle"}]}}
etc.

Answer 2

Here is a query
db.collection.aggregate([
{$match: {name:"Test"}},
{$project: {
name:"$name",
country: "$country",
city:"$city",
countryMatch: {$cond: [{$eq:["$country", "USA"]}, true, false]},
cityMatch: {$cond:[{$eq:["$city", "Seattle"]}, true, false]}
}},
{$match: {$and: [
{$or:[{countryMatch:true},{country:""}]},
{$or:[{cityMatch:true},{city:""}]}
]}},
{$sort: {countryMatch:-1, cityMatch:-1}},
{$project: {name:"$name", country:"$country", city:"$city"}}
])
Explanation:
First match filters out docs which don't match name (because rule #1 - name should match).
Next projection selects doc fields plus some information about country and city matches. We will need it to further filter and sort documents.
Second match filters out those documents which don't match both country and city and don't have default values for these fields (rule #3).
Sorting documents moves country matches before city matches as rule #2 states. And last - projection selects required fields.
Output:
{
_id: 3,
name : "Test",
country : "USA",
city : ""
},
{
_id: 1,
name : "Test",
country : "",
city : "Seattle"
}
You can limit query results to get only closest match.