Transactions

The client also has a .transaction() method that allows for atomic transactions.

Wikipedia has a good example of a scenario requiring a transaction which we can then implement:

An example of an atomic transaction is a monetary transfer from bank account A to account B. It consists of two operations, withdrawing the money from account A and saving it to account B. Performing these operations in an atomic transaction ensures that the database remains in a consistent state, that is, money is neither lost nor created if either of those two operations fails.

A transaction removing 10 cents from one customer’s account and placing it in another’s would look like this:

Copy

#[derive(Debug, Deserialize, Queryable)]
pub struct BankCustomer {
    pub name: String,
    pub bank_balance: i32,
}
// Customer1 has an account with 110 cents in it.
// Customer2 has an account with 90 cents in it.
// Customer1 is going to send 10 cents to Customer 2. This will be a
// transaction as we don't want the case to ever occur - even for a
// split second - where one account has sent money while the other
// has not received it yet.

// After the transaction is over, each customer should have 100 cents.

let sender_name = "Customer1";
let receiver_name = "Customer2";
let balance_check = "select BankCustomer { name, bank_balance }
    filter .name = <str>$0";
let balance_change = "update BankCustomer
        filter .name = <str>$0
        set { bank_balance := .bank_balance + <int32>$1 }";
let send_amount = 10;

client
    .transaction(|mut conn| async move {
        let sender: BankCustomer = conn
            .query_required_single(balance_check, &(sender_name,))
            .await?;
        if sender.bank_balance < send_amount {
            println!("Not enough money, bailing from transaction");
            return Ok(());
        };
        conn.execute(balance_change, &(sender_name, send_amount.neg()))
          .await?;
        conn.execute(balance_change, &(receiver_name, send_amount))
          .await?;
        Ok(())
    })
    .await?;

What often may seem to require an atomic transaction can instead be achieved with links and backlinks which are both idiomatic and easy to use in EdgeDB. For example, if one object holds a required link to two other objects and each of these two objects has a single backlink to the first one, simply updating the first object will effectively change the state of the other two instantaneously.

Transactions​

Transactions