greater_than_less_than.md

Greater Than / Less Than

If values of an entry are numbers, we can compare the sizes of the values when we retrieve documents. We can filter the documents that have the entry value larger (or smaller) than a given entry value.

collection.find(doc! {"Height": {"$gt": 185}}).unwrap();

The example above finds the documents with Height larger than 185.

In addition to $gt, we can use $lt for less than, $gte for greater than or equal to, and $lte for less than or equal to.

The complete code is presented below:

use polodb_core::{bson::doc, Database};

fn main() {
    let db = Database::open_memory().unwrap();
    let collection = db.collection("name_of_the_collection");

    let docs = [
        doc! {
            "Name": "Alice",
            "Age": 21,
            "Height": 190,
        },
        doc! {
            "Name": "Bob",
            "Age": 20,
            "Height": 180,
        },
        doc! {
            "Name": "Cat",
            "Age": 3,
        },
    ];
    collection.insert_many(docs).unwrap();

    let docs_found = collection.find(doc! {"Height": {"$gt": 185}}).unwrap();
    for doc in docs_found {
        println!("{:#?}", doc.unwrap());
    }
}

Output:

Document({
    "Name": String(
        "Alice",
    ),
    "Age": Int32(
        21,
    ),
    "Height": Int32(
        190,
    ),
    "_id": ObjectId(
        "66ba285f89a2c920077fb007",
    ),
})

Note that, since Cat has no Height entry, it will not be output.

➡️ Next: Any One In An Array

📘 Back: Table of contents