connect-pgclient

Connect middleware to manage Postgres connections.

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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(reqresnext) {
        // here you can use req.db.client to perform queries 
        next();
    },
    function(reqres) {
        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(reqres) {
        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(reqres) {
        res.send('Ok');
    }
);

Using connect-pgclient you'll be able to do this:

app.get(
    '/',
     // middleware you created using connect-pgclient 
    dbMiddleware,
    selectSomethingFromDb,
    function(reqres) {
        if ( somethingWasntFound ) {
            return res.redirect('/');
            // client is automatically released 
        }
        next();
    },
    function(reqres) {
        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(reqres) {
        res.send('My Homepage - Under Construction!');
    }
);
 
// a route which redirects 50% of the time - Pg client is released ok 
app.get(
    '/random',
    connectToDb,
    function(reqres) {
        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(reqresnext) {
        // this is how you get your freshly minted Postgres client 
        req.db.client("SELECT now()", next);
    },
    function(reqresnext) {
        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.)

Author

Written by Andrew Chilton - Blog - Twitter.

License

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