Store expression/condition in document - mongodb

Question

I'm new to mongodb and am unable to figure out if the below is even possible.
Can I store a condition, such as gt, lt, etc., inside a field in a document and then utilize it in a query?
So, given the following documents:
{
title : "testTitle1",
score : 55,
condition : "gt"
}
{
title : "testTitle2",
score : 30,
condition : "lt"
}
And given an inputScore = 75, only testTitle1 document would be returned because 75 is greater than ("gt") 55. The second document would not be returned because it is not less than ("lt") 30.
Any ideas?
Thanks

Answer 1

Yes, you can the params passed to the query is simply an object. You will need to use the mongodb operators unless you want to add additional processing before you send the query.
As an example:
const data = {
title : "testTitle1",
score : 55,
condition : "$gt"
};
const query = {
score: {}
};
query.score[data.condition] = data.score;
console.log(query);
Example with additional operator conversion:
const data = {
title : "testTitle1",
score : 55,
condition : "gt"
};
const query = {
score: {}
};
switch (data.condition) {
case "gt":
query.score["$gt"] = data.score;
break;
case "lt":
query.score["$lt"] = data.score;
break;
}
console.log(query);

Answer 2

if you want pure mongodb query, you can use $expr operator in your query or aggregation.
db.collection.find({
$expr: {
$or: [
{
$and: [
{$eq: ['$condition', 'gt']},
{$gt: [75, '$score']}
]
},
{
$and: [
{$eq: ['$condition', 'lt']},
{$lt: [75, '$score']}
]
}
]
}
})
i hope you get the idea

Answer 3

The query is with aggregation framework. I use the $switch for checking if the conditionhas a gt or lt value and return a trueor false after the inputScore is compared with the score. This compared result matches gives the filter condition to include or reject the input document.
var inputScore = 75;
db.gtlt.aggregate( [
{ $addFields: {
matches: {
$switch: {
branches: [
{
case: { $eq : [ "$condition", "gt" ] },
then: { $cond: [ { $gt: [ inputScore, "$score" ] }, true, false ] }
},
{
case: { $eq : [ "$condition", "lt" ] },
then: { $cond: [ { $lt: [ inputScore, "$score" ] }, true, false ] }
},
],
default: false
}
}
} },
{ $match: { matches: true } },
{ $project: { matches: 0 } }
] )