express.md

npm mssql

Connections are expensive. Use them for one time open/close operations. Otherwise, use a pool when executing a series of queries.

Async/Await

router.get("/api", async (req, res) => {

        let id = req.query.id;

        try {
            const connection = await sql.connect(db);
            const request = await connection.request()

            request.input("id", sql.Int, id);

            let query = `
                select *
                from products
                where id = @id
            `

            let result = await request.query(query)

            res.send(result)

        } catch (err) {
            console.log("Error: " + err);
        } finally {
            sql.close();
        };
})

Promise

new sql.ConnectionPool(db)
    .connect()
    .then((pool) => {
        return pool.request().query("SELECT * FROM product");
    })
    .then((result) => {
        let rows = result.recordset;
        res.setHeader("Access-Control-Allow-Origin", "*");
        res.status(200).json(rows);
        sql.close();
    })
    .catch((err) => {
        res.status(500).send({ message: "${err}" });
        sql.close();
    });

Callback

sql.connect(db, function (err) {
    if (err) console.log(err);
    var request = new sql.Request();
    request.query("SELECT * FROM product", function (err, recordset) {
        if (err) console.log(err);

        let rows = recordset.recordsets[0];
        res.send(rows);
        sql.close(); // Important
    });
});

JSON

JSON is used to transfer data via a string.

An object from one programming language can be transferred to another by encoding it in JSON and then decoding it, even though they cannot understand each others' objects.

// Javascript object literal.
var personObject = {
    firstName:"John",
    lastName:"Doe",
    age:50,
    eyeColor:"blue"
};

// Convert object to JSON.
var personJSON = JSON.stringify(personObject);

// personJSON.
{
    "firstName":"John",
    "lastName":"Doe",
    "age":50,
    "eyeColor":"blue"
}

// Convert JSON to object.
JSON.stringify(personJSON);