So I have the following promise that is supposed to go inside my sqlite database and tell me if there is a match. Even if the variables are correct it always returns undefined.
var checkLoanable = function(bookID){
return new Promise((resolve, reject)=>{
db.run('SELECT * FROM book WHERE id=?',[bookID],(err,row)=>{
if (err) {
console.log("error")
reject();
}
if(row){
if(row.loanable==0){
console.log("not loanable")
reject();
}
console.log("success")
resolve(row);
}else{
console.log("undefined")
reject();
}
console.log("End of promise")
});
})
}
This is the call of the function
await checkLoanable(bookID)
.then(()=>{console.log("success")})
.catch(()=>{
res.status(422)
.setHeader('content-type', 'application/json')
.send({ message: "Failed to add loan: book is not loanable!"});
});
console.log("after promise");
The await is inside an async function and after tests I did it does wait for the promise to end and then continues the code. I can't figure out why its always undefined though. Thank you in advance for any help.
run() is used for inserting and updating rows.
For getting a single row use db.get().
db.get('SELECT * FROM book WHERE id=?', [bookID] , (err,row) => { });
At least if you are using the npm/sqlite package.
Do not mix async/await and Promise chain use one of them.
Either with try...catch or Promise..then..catch
try {
const book = await checkLoanable(bookID);
res.json(book);
}catch ({message}) {
res.status(422).send(message);
}
// or
checkLoanable(bookID)
.then((book) => {res.json(book);})
.catch(({message}) => {
res.status(422).json({
message: "Failed to add loan: book is not loanable!"
});
});
For the example if you use something like this
const myPromise = () => new Promise((resolve, reject) => {
setTimeout(() => {
resolve('Success!');
}, 1000);
});
(async () => {
const result = await myPromise().then(data => {
console.log({data});
});
console.log({result});
})();
Result would be
{data: 'Success!'}
{result: undefined}
Not both get values at the same time.