creating_indexes.md

Creating Indexes

We can create indexes for better searching performance. Without an index, PoloDB has to read all documents to search for a particular document. Indexes let PoloDB read less documents while it is looking for some documents.

We use create_index to create an index.

collection.create_index(IndexModel {keys: doc! {"Age": 1}, options: None,}).unwrap();

Method create_index needs an IndexModel, which needs keys and options. keys are the entry names that we would like to build an index on. We specify doc! {"Age": 1} here, where 1 indicates that the entry is sorted in ascending order. options will be introduced later.

The complete code is shown below:

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

fn main() {
    let db = Database::open_memory().unwrap();
    let collection = db.collection("name_of_the_collection");
    
    collection
        .create_index(IndexModel {
            keys: doc! {
                "Age": 1,
            },
            options: None,
        })
        .unwrap();
    
    let docs = [
        doc! {
            "Name": "Alice",
            "Age": 21,
        },
        doc! {
            "Name": "Bob",
            "Age": 20,
        },
        doc! {
            "Name": "Cat",
            "Age": 3,
        },
    ];
    collection.insert_many(docs).unwrap();
    
    let docs_found = collection
        .find(doc! {
            "Age": doc! {"$eq": 20}
        })
        .unwrap();
    for doc in docs_found {
        println!("{:#?}", doc.unwrap());
    }
}

Output:

Document({
    "Name": String(
        "Bob",
    ),
    "Age": Int32(
        20,
    ),
    "_id": ObjectId(
        "66f1591edb03e4fd392164e6",
    ),
})

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