connect-pgclient v0.3.0
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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-pgclientconnect-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.
Example
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
);What does this package solve?
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
);Usage
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.transactionIn general, you should only ever use the req.db.client property of req.db.
Options
- 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)
Examples
Connect to DB for Every Request
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,
}));Connect to the DB within Specific Routes
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!');
}
}
);How it Works
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.
Caveat
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.)
Author
Written by Andrew Chilton - Blog - Twitter.
License
(Ends)