pg-promise - Not resolving multiple queries - postgresql

Question

I'm in the process of creating a mass mailer that allows a company to send out an email template to a specific plan that contains X amount of subscribers.
However, when using pg-promise, I can't figure how to loop through an array that contains one or more unique plan names that'll then be used as query parameters for subsequent queries to gather a single array of results. The subsequent queries don't resolve before express sends back a specified error message.
For example:
const selectedTemplate = await db.oneOrNone("SELECT * FROM templates WHERE userid=$1 and uniqueTemplateName=$2", [req.session.id, req.body.uniquetemplatename])
returns a JSON object...
{ ...
plans : [ 'Unique Plan 1', 'Unique Plan 2', 'Unique Plan 3'...],
...
}
I then want to loop through this plans array to gather some subscriber emails. Since the selectedTemplate's plans array can contain a single "Unique Plan" or multiple, I'm trying to figure out how to get this query to work:
let subscriberEmails = [];
await each(selectedTemplate.plans, async plan => {
const emails = await db.any("SELECT email FROM subscribers WHERE userid=$1 AND planName=$2", [req.session.id, plan])
each(emails, ({email}) => subscriberEmails.push(email))
console.log('Found emails: ', subscriberEmails);
})
console.log('Selected emails: ', subscriberEmails);
res.status(500).json({ message: "Route not configured yet" })
The problem I'm having is that Express isn't waiting for the pg-promise to resolve. So it's triggering my 500 server "Route not configured yet" message, then resolves the queries:
14:48:33 SELECT * FROM templates WHERE userid='12345' and uniqueTemplateName='example-unique-template'
selectedTemplate: anonymous {
id: '84efa448-b149-11e8-a7fd-3b9e4e9e5ece',
key: 9,
userid: '12345',
status: 'active',
fromsender: 'example#helpdesk.com',
subject: 'Thank you for using our services!',
templatename: 'Example Unique Template',
uniquetemplatename: 'example-unique-template',
message: '<h3>This is a test!</h3>',
plans: [ 'Unique Plan 1', 'Unique Plan 2' ]
}
Selected emails: []
POST /api/messages/create 500 28 - 34.125 ms
14:48:33 SELECT email FROM subscribers WHERE userid='12345' AND planName='Unique Plan 1'
Found emails: [
'betatester19#example.com',
'betatester20#example.com',
'betatester21#example.com'
]
14:48:34 SELECT email FROM subscribers WHERE userid='12345' AND planName='Unique Plan 2'
Found emails: [
'betatester19#example.com',
'betatester20#example.com',
'betatester21#example.com',
'betatester1#example.com',
'betatester2#example.com',
'betatester3#example.com',
'betatester4#example.com',
'betatester5#example.com',
'betatester6#example.com',
'betatester7#example.com',
'betatester8#example.com',
'betatester9#example.com',
'betatester10#example.com',
'betatester11#example.com',
'betatester12#example.com',
'betatester13#example.com',
'betatester14#example.com',
'betatester15#example.com',
'betatester16#example.com',
'betatester17#example.com',
'betatester18#example.com'
]
The function as is:
async (req, res, done) => {
if (!req.body) {
return res.status(404).json({ message: "Missing query parameters" });
done();
}
try {
const selectedTemplate = await db.oneOrNone("SELECT * FROM templates WHERE userid=$1 and uniqueTemplateName=$2", [req.session.id, uniquetemplatename]);
if (!selectedTemplate) {
return res.status(404).json({ message: "Unable to locate selected template" });
done();
}
console.log('selectedTemplate', selectedTemplate);
let subscriberEmails = [];
await each(selectedTemplate.plans, async plan => {
const emails = await db.any("SELECT email FROM subscribers WHERE userid=$1 AND planName=$2", [req.session.id, plan])
each(emails, ({email}) => subscriberEmails.push(email))
console.log('Found emails: ', subscriberEmails);
})
console.log('Selected emails: ', subscriberEmails);
res.status(500).json({ message: "Route not configured yet" })
} catch (err) { res.status(500).json({ message: err }); done(); }
}
A vastly simplified DB structure:
├── Template
│ └── Plans (references an array of unique plan name(s))
|
|── Plan
| └── PlanName (unique plan name)
|
│── Subscriber
| └── PlanName (references a single unique plan name)
| └── Email (unique email)
I've tried using a db.task(), but again, the queries didn't resolve before Express sent back the message.

Answer 1

Figured out where the problem was. Just in case anyone else stumbles upon this predicament: Functions like "map" and "each" don't handle async/await. They instead just return a pending Promise. Therefore, you'll want to use a library like Bluebird, which implements Promise-based each/map/etc functions (found under "Collections").
The fix for the above to work:
try {
await db.task('create-message', async t => {
const selectedTemplate = await t.oneOrNone(findTemplateByName, [req.session.id, uniquetemplatename])
if (!selectedTemplate) return sendError(unableToLocate('template'), res, done);
const { fromsender, subject, message, plans, templatename } = selectedTemplate;
let subscriberEmails = [];
await Promise.each(plans, async plan => {
const emails = await t.any(getAllEmailsByPlan, [req.session.id, plan]);
each(emails, ({email}) => subscriberEmails.push(email));
})
if (isEmpty(subscriberEmails)) return sendError(unableToLocate('subscribers in the selected plan(s)'), res, done);
const msg = {
to: subscriberEmails,
from: fromsender,
replyTo: fromsender,
subject: subject,
html: message
};
await mailer.sendMultiple(msg);
await t.none(createMessageTransaction, [req.session.id, templatename, fromsender, subject, currentDate, plans]);
await t.none(createNotification, [req.session.id, 'mail_outline', `The following template: ${templatename} has been sent out to the subscibers in the following ${plans.length > 1 ? "plans" : "plan"}: ${plans}.`, date]);
return res.status(201).send(null);
})
} catch (err) { return sendError(err, res, done); }