MongoDB query that shows how many fields document matches - node.js

Question

I am creating a MERN app that allows users to sign up and save their skills to a database. I am creating an admin panel that allows me to search for users by skill. User's skills will look like this in the database:
skills: [
{skill: 'React', yearsExperience: 3},
{skill: 'HTML', yearsExperience: 5},
{skill: 'JavaScript', yearsExperience: 5},
{skill: 'Git', yearsExperience: 3},
{skill: 'TypeScript', yearsExperience: 1},
{skill: 'C++', yearsExperience: 1}
]
I am using OR queries to query the database to pull back users who match several requirements like this (User's with greater than 3 years experience in C, or users with greater than 3 years experience in SQL):
$or: [
{ skills: { $elemMatch: { skill: 'C', yearsExperience: { $gt: 3 } } } },
{ skills: { $elemMatch: { skill: 'SQL', yearsExperience: { $gt: 3 } } } },
];
My question is, how can I return the users in an array with a property called percentageMatch that shows how many fields the query searched for that they matched? For example, if Mark has both C and SQL experience with greater than 3 years his property will say 100%, but if James has only 3 years or greater of SQL experience, and no C experience his percentageMatching will say 50%.
// Response of match query
[
{
name: 'Mark',
skills: [...],
percentageMatch: 100%
},
{
name: 'James',
skills: [...],
percentageMatch: 50%
}
]

Answer 1

You can do it with aggregation,
$match to get your desired document
$filter to filter the array based on your condition and assign it to matchingSkills using $addFields
then get the percentage using $multiply, $divide.
Here is the code
db.collection.aggregate([
{
"$match": { name: "mark" }
},
{
$addFields: {
matchingSkills: {
$filter: {
input: "$skills",
cond: {
$or: [
{
$and: [
{ $gt: [ "$$this.yearsExperience", 3 ] },
{ $eq: [ "$$this.skill", "HTML" ]}
]
},
{
$and: [
{ $gt: [ "$$this.yearsExperience", 3] },
{ $eq: [ "$$this.skill", "Git"] }
]
}
]
}
}
}
}
},
{
$addFields: {
matchingSkills: "$$REMOVE",
percentageMatch: {
$multiply: [
{ $divide: [ { $size: "$matchingSkills" }, 2 ]}, // yu already know how many values you need to pass, thats' why `2`
100
]
}
}
}
])
Working Mongo playground