How to find documents from a mongoose schema, given an array of objects with IDs-CodePudding

I am trying to find some documents given an array of objects and inside each object, there is an id "courseId" which will be used to find the required documents from the schema with the same id. Here is the array of objects:

courseIds =  [
{"courseId":"638c139b147e2173163fd976",
"_id":"63906c07b9b09cd81e48480d"
},
{"courseId":"638c131a147e2173163fd96b",
"_id":"63908c9f1897b57aa6ece69f"
}]

and if the schema contains the following objects:

const courseSchema =
[{
"_id":"638c131a147e2173163fd96b",
"courseTitle":"Neural Networks",
"price":"5000",
"shortSummary":"Its a lovely course about NNs, Sequence Models.",
"subject":"Deep Learning"
},
{
"_id":"638c139b147e2173163fd976",
"courseTitle":"Graphics",
"price":"3000",
"shortSummary":"Its a lovely course about Projection, 2D & 3D Transformations.",
"subject":"Computer Graphics"
},
{
"_id":"638c131a147e9053163fd281",
"courseTitle":"Operating Systems",
"price":"4500",
"shortSummary":"Its a lovely course about Scheduling, learning about drivers and peripherals.",
"subject":"Hardware"
}]

What I want to do is I want to find/return only the courses from the courseSchema whose ids are present in the courseIds array, like here it would only return two courses:

{
"_id":"638c131a147e2173163fd96b",
"courseTitle":"Neural Networks",
"price":"5000",
"shortSummary":"Its a lovely course about NNs, Sequence Models.",
"subject":"Deep Learning"
},
{
"_id":"638c139b147e2173163fd976",
"courseTitle":"Graphics",
"price":"3000",
"shortSummary":"Its a lovely course about Projection, 2D & 3D Transformations.",
"subject":"Computer Graphics"
}

since their ids "_id" are present in the courseIds array ("courseId == _id").

I tried to do the following:

const docs = courseSchema.find().where('_id').in(courseIds);

and

const docs = courseSchema.find({ '_id': { $in: courseIds} });

and it always return an empty array (no matches). Why doesn't it work?

CodePudding user response：

courseIds id a array object, in order to match _id with $in the array must be of only _id like ["638c139b147e2173163fd976","638c131a147e2173163fd96b"].

for that you can make another array from courseIds array object and use that as in query with $in.

    courseIds =  [
        {
            "courseId":"638c139b147e2173163fd976",
            "_id":"63906c07b9b09cd81e48480d"
        },
        {
            "courseId":"638c131a147e2173163fd96b",
            "_id":"63908c9f1897b57aa6ece69f"
        }
    ] //Your courseIds array object

    let onlyIds=[] // declaring array to store only _ids

    for(let i=0;i<courseIds.length;i  ){
        if(!onlyIds.includes(courseIds[i].courseId)) //checking id exist in array, if not exist push _id to onlyIds aarray
            onlyIds.push(courseIds[i].courseId); //push _id
    }

    console.log(courseId)//output=>["638c139b147e2173163fd976","638c131a147e2173163fd96b"]
    const docs = courseSchema.find({ _id: { $in: onlyIds } }); //final query