alpian

#!/bin/sh
# Installs the QLDB Shell on AWS CloudShell
VERSION="2.0.0-alpha3"
sudo yum install -y -q openssl11-libs
mkdir qldb
curl -sL https://github.com/awslabs/amazon-qldb-shell/releases/download/v$VERSION/qldb-v$VERSION-linux.tar.gz | tar zx -C qldb && export PATH=$PATH:~/qldb/qldb-v$VERSION-linux
echo "Run qldb --ledger <your-ledger> to start the shell"
echo "Run \`echo \"export PATH=\$PATH:~/qldb/qldb-v$VERSION-linux\" >> ~/.bashrc\` to append this to your path"

alpian

async function betterGrabMovieTickets(qldb: QldbDriver, seat: string) {
    const [allocationTime, message] =
        await qldb.executeLambda( async txn => {
            const result = await txn.execute(
                "select * from Showing where seat = ? and allocated = ?",
                seat, false);
            const allocationTime = Date.now();
            if (result.getResultList().length === 1) {
                await txn.execute(
                    "update Showing set allocated = ? where seat = ?",

alpian

let state = { seat: "a5" };
async function badGrabMovieTickets(qldb: QldbDriver) {
    // DO NOT USE: This code is deliberately wrong to show what pitfalls to avoid
    let allocationTime;
    await qldb.executeLambda(async txn => {
        // BAD: don't rely on state from outside the function parameters
        const result = await txn.execute(
            "select * from Showing where seat = ? and allocated = ?",
            state.seat, false);
        // BAD: cannot change external state from inside the function

alpian

async function grabMovieTickets(qldb: QldbDriver, seat: string) {
    await qldb.executeLambda(async txn => {
        const result = await txn.execute(
            "select * from Showing where seat = ? and allocated = ?",
            seat, false);
        if (result.getResultList().length === 1) {
            await txn.execute(
                "update Showing set allocated = ? where seat = ?",
                true, seat);
            return "you got the seat!";

alpian

// Scala code:
//
// trait MyTrait {
//   def someImplementation() = {
//     println("Implementation in an interface")
//   }
//
//   def pureVirtualFuntion()
// }

alpian

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