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| ( \/| ( ) || \ ( || \ ( || ( \/| ( \/ ) (
| | | | | || \ | || \ | || (__ | | | |
| | | | | || (\ \) || (\ \) || __) | | | |
| | | | | || | \ || | \ || ( | | | |
| (____/\| (___) || ) \ || ) \ || (____/\| (____/\ | |
(_______/(_______)|/ )_)|/ )_)(_______/(_______/ )_(
_______ _______ _______ _ _________ _______ _ _________
( ____ )( ____ \( ____ \( \ \__ __/( ____ \( ( /|\__ __/
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_____ | (____)|| | | | | | | | | (__ | \ | | | |
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| ( | | \_ )| | | | | | | ( | | \ | | |
| ) | (___) || (____/\| (____/\___) (___| (____/\| ) \ | | |
|/ (_______)(_______/(_______/\_______/(_______/|/ )_) )_(
This module is aimed at taking the pain away from managing your Postgres connections from within a connect/express
app. Too many times has res.redirect()
been used and left the DB connection hanging.
npm install connect-pgclient
connect-pgclient
helps you manage (and free) your Postgres database connections so you don't have to. It
automatically gets a client from node-pg
at the start of the request and calls done()
at the end of the
request to automatically return the client back to pg's pool. This way you'll never lose any clients by accidentally
not calling done
.
var pgclient = require('connect-pgclient');
var dbMiddleware = pgclient({
config : {
database : 'dbname',
user : 'me',
host : 'dbserver.internal',
},
});
app.get(
'/',
dbMiddleware,
function(req, res, next) {
// here you can use req.db.client to perform queries
next();
},
function(req, res) {
res.send('Ok');
}
// req.db.done is automatically called to release the client
);
If you are trying to do your Pg clients manually, then there are various cases which you might forget about where you
should call done()
. Here is an example when you have a client but call res.redirect()
and forget to release
it again:
app.get(
'/',
connectToDb,
selectSomethingFromDb,
function(req, res) {
if ( somethingWasntFound ) {
return res.redirect('/');
// bang, you just lost a DB client
}
next();
},
// must remember to release here, otherwise you'll lose another DB client
disconnectFromDb,
function(req, res) {
res.send('Ok');
}
);
Using connect-pgclient
you'll be able to do this:
app.get(
'/',
// middleware you created using connect-pgclient
dbMiddleware,
selectSomethingFromDb,
function(req, res) {
if ( somethingWasntFound ) {
return res.redirect('/');
// client is automatically released
}
next();
},
function(req, res) {
res.send('Ok');
}
// client is automatically released
);
Once you have setup and called your connect-pgclient
middleware, you Postgres client is available on the
req
object as follows:
// the node-pg client
req.db.client
// the done function which node-pg needs to return the client to the pool
req.db.done
// boolean to show us whether we are in the middle of a transaction
req.db.transaction
In general, you should only ever use the req.db.client
property of req.db
.
- config - the database connection params as defined in node-postgres
- transaction - (default: false) States whether to BEGIN and COMMIT a transaction for you.
- log - (default: no-op) a function to call with log messages to help with debugging (usually dev only)
You may or may not want to do this, but it shows a good example for starters:
var pgclient = require('connect-pgclient');
app.use(pgclient({
config : {
database : 'dbname',
user : 'me',
host : 'dbserver.internal',
},
}));
If you would like connect-pgclient
to BEGIN and COMMIT a transaction for you, then just pass the
transaction
param as true
into the options.
var pgclient = require('connect-pgclient');
app.use(pgclient({
config : {
database : 'dbname',
user : 'me',
host : 'dbserver.internal',
},
transaction : true,
}));
The database clients are released back to node-pg
even if the request ends in res.send()
,
res.redirect()
, res.json()
, res.render()
or even in error next(err)
.
For example:
// Postgres middleware which gets a Pg client and releases it after
// the request has been fulfilled.
var connectToDb = pgclient({
config : {
database : 'dbname',
user : 'me',
host : 'dbserver.internal',
},
});
// Postgres middleware which gets a Pg client, starts a transaction
// and commits and releases it after the request has been fulfilled.
var connectToDbWithTransaction = pgclient({
config : {
database : 'dbname',
user : 'me',
host : 'dbserver.internal',
},
transaction : true,
});
// a route which always succeeds - Pg client is released ok
app.get(
'/',
connectToDb,
function(req, res) {
res.send('My Homepage - Under Construction!');
}
);
// a route which redirects 50% of the time - Pg client is released ok
app.get(
'/random',
connectToDb,
function(req, res) {
if ( Math.random() < 0.5 ) {
// even though we're not calling node-pg's done(), connect-pgclient does it for us even here
res.redirect('/');
}
else {
res.send('My Homepage - Under Construction!');
}
}
);
// a route which dies 50% of the time - Pg client is released ok
app.get(
'/roulette',
connectToDbWithTransaction,
function(req, res, next) {
// this is how you get your freshly minted Postgres client
req.db.client("SELECT now()", next);
},
function(req, res, next) {
if ( Math.random() < 0.5 ) {
// even though we're not calling node-pg's done(), connect-pgclient does it for us even here
next(new Error("Die die die!"));
}
else {
res.send('My Homepage - Under Construction!');
}
}
);
Using brianc's excellent pg library, we connect to the
database and store both the client
and the done
function onto the req
so that we can use the client
in our routes, but also automatically call done
when the request has finished.
connect-pgclient
works much like connect's session
middleware in that it wraps res.end()
so that we
can get control both before and after the request has been fulfilled, which allows us to give the client back to pg's
pool automatically no matter what happened during the request.
When you use connect-pgclient
to give you a client and automatically start a transaction, if the request ends up
in error, the transaction still has COMMIT
performed. In this error case, I think ROLLBACK
should be called
instead but I'm not yet sure how to detect if the request is in the error state.
(Note: remember that this is after the request has been fulfilled, which is after any error middleware has been run.)
Written by Andrew Chilton - Blog - Twitter.
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