Mongo filter documents by array of objects

Question

I have to filter candidate documents by an array of objects.

In the documents I have the following fields:

skills = [
  { _id: 'blablabla', skill: 'Angular', level: 3 },
  { _id: 'blablabla', skill: 'React', level: 2 },
  { _id: 'blablabla', skill: 'Vue', level: 4 },
];

When I make the request I get other array of skills, for example:

skills = [
  { skill: 'React', level: 2 },
];

So I need to build a query to get the documents that contains this skill and a greater or equal level.

I try doing the following:

const conditions = {
  $elemMatch: {
    skill: { $in: skills.map(item => item.skill) },
    level: { $gte: { $in: skills.map(item => item.level) } }
  }
};

Candidate.find(conditions)...

The first one seems like works but the second one doesn't work.

Any idea?

Thank you in advance!

Alex Blex · Accepted Answer · 2020-05-27 17:15:02Z

There are so many problems with this query...

First of all item.tech - it had to be item.skill.

Next, $gte ... $in makes very little sense. $gte means >=, greater or equal than something. If you compare numbers, the "something" must be a number. Like 3 >= 5 resolves to false, and 3 >= 1 resolves to true. 3 >= [1,2,3,4,5] makes no sense since it resolves to true to the first 3 elements, and to false to the last 2.

Finally, $elemMatch doesn't work this way. It tests each element of the array for all conditions to match. What you was trying to write was like : find a document where skills array has a subdocument with skill matching at least one of [array of skills] and level is greater than ... something. Even if the $gte condition was correct, the combination of $elementMatch and $in inside doesen't do any better than regular $in:

{
    skill: { $in: skills.map(item => item.tech) },
    level: { $gte: ??? }
}

If you want to find candidates with tech skills of particular level or higher, it should be $or condition for each skill-level pair:

const conditions = {$or: 
    skills.map(s=>(
        {skill: { $elemMatch: {
            skill:s.skill, 
            level:{ $gte:s.level }
        } } }
    ))
};

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