Mongoose get latest document for every unique value in field-CodePudding

I have a Mongoose schema which is like this:

const mySchema = new mongoose.Schema(
  {
    _id: String,
    coin: String,
    closeTime: Number,
    volume: Number,
  }

I have a bunch of different coins. Is it possible to get the latest document for each unique coin I have based on the closeTime?

Help would be much appreciated! Thanks.

CodePudding user response：

You can use aggregation to sort by latest/newest closeTime, group by coin then getting the first document of that group:

mySchema.aggregate([
  { $sort: { closeTime: -1 } },
  { $group: { _id: "$coin", latest: { $first: "$$ROOT" } } }
])

This is sorting with numeric closeTime in descending order, getting the first/latest document and putting its data into a property called latest. This should create results like:

[{
    "_id" : "2",
    "latest" : {
        "_id" : ObjectId("6149f106742bb30e2529c453"),
        "coin" : "foo",
        "closeTime" : 5,
        "volume" : 1
    }
}
{
    "_id" : "1",
    "latest" : {
        "_id" : ObjectId("6149f111742bb30e2529c45f"),
        "coin" : "bar",
        "closeTime" : 4,
        "volume" : 1
    }
}]

You can take this one step further with other aggregation stages to extract/project the underlying coin document.