MongoDB: How do I find coordinates nearby?-CodePudding

In this function, I want to check if there are any posts in the database made nearby to a set of input lat/long coords so that I can display them based on where the user currently is, and I also want to write a function to check if they are in a "too close" range (less than 2m or so).

I'm not sure how to do it properly and every answer I have found online after extensive research has given me nothing. I am using NodeJS 18 LTS with the latest version of mongodb.

This is the code I tried to get the posts

const getPostsInRange = (lng, lat) => {

    // get all posts in range
    const postCollection = db.collection('posts')

    return postCollection.find({
        "location": {
            "$near": [parseFloat(lng), parseFloat(lat)],
            "$maxDistance": 100000
        }})


}

and here is the code that calls it, from index.js

app.get('/getposts/:lat/:long', requiresAuth(), (req, res) => {

    const { lat, long } = req.params

    getPostsInRange(long, lat)
        .then((posts) => {

            res.send(posts)

        })
        .catch((err) => {
            console.log(err)
            res.status(500).end()
        })

what my data looks like in mongodb:

{
        "textBody": "new message 3",
        "image": "xxxx",
        "location": {
            "type": "Point",
            "coordinates": [xxxx, xxxx]
        },
        "timestamp": 1674503437
}

I get errors such as TypeError: getPostsInRange(...).then is not a function, and similar but slightly different ones that Google seems to have never have heard of.

i would love some help building this project, full code snippets would be greatly appreciate due to my lack of experience working with mongodb.

CodePudding user response：

It looks like the issue is with the getPostsInRange function not returning a Promise, which is necessary for the .then and .catch to work. The find method from the MongoDB Node.js driver returns a Cursor, which is not a Promise but does have a toArray method that can be used to convert the results to an array and return a Promise.

Here is an example of how you can modify the getPostsInRange function to return a Promise:

const getPostsInRange = (lng, lat) => {

    // get all posts in range
    const postCollection = db.collection('posts')

    return postCollection.find({
        "location": {
            "$near": [parseFloat(lng), parseFloat(lat)],
            "$maxDistance": 100000
        }
    }).toArray();
}

This will make the getPostsInRange function return a Promise that resolves with an array of posts.

It is also worth mentioning that the $near operator requires MongoDB to have a 2dsphere index on the location field, which you can create by running the following command in your MongoDB shell:

db.posts.createIndex({ location: "2dsphere" })

Also you need to make sure that your location object in the document is in the correct format like {type:"Point",coordinates:[long,lat]}.

Hope this helps!