finding_at_most_one_document.md

Finding At Most One Document

Previously, we use find to find all the documents that satisfy the given entry conditions. We can restrict ourselves to find only at most one document by find_one.

collection.find_one(doc! {"Age": {"$gt": 10}}).unwrap();

The example above finds the first document that has Age more than 10.

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,
        },
        doc! {
            "Name": "Bob",
            "Age": 20,
        },
        doc! {
            "Name": "Cat",
            "Age": 3,
        },
    ];
    collection.insert_many(docs).unwrap();
    
    let doc_found = collection.find_one(doc! {"Age": {"$gt": 10}}).unwrap();
    println!("{:#?}", doc_found.unwrap());
}

Now that there is at most one returned document, we do not need to use a for loop to go through all the documents. Instead, we can manipulate the returned document directly.

Output:

Document({
    "Name": String(
        "Alice",
    ),
    "Age": Int32(
        21,
    ),
    "_id": ObjectId(
        "66d843923f8193105d066f6a",
    ),
})

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