Pg-promise: Verify database connection or throw?

[reinvantveer]

Hi,

Thanks for your nice package. I have a question: while writing tests, I try to check for unsuccessful connections. In a lot of situations, one can't simply assume the availability of the database, one has to test for it. The

var db = pgp(connectionObject);

doesn't seem to throw an error. It isn't a promise either. So when I put in garbage in the connectionObject, I expect to be able to test for an

assert.throws(function shouldThrow(){
var db = pgp("postgres://this:is/just:999/silly");

db.query("select '1'::int as number", true)
.then(function(result){console.log(result)})
.catch(
//re-throw error here, you know the deal
);
});

(this is probably pseudo-code by the way)

But instead of throwing, it just gives me an empty result. Any ideas on how to reliably test?

Thanks a bunch,
Rein

[vitaly-t]

For that you should use connect and error events.

See how pg-promise does it when testing itself:

• https://github.com/vitaly-t/pg-promise/blob/master/test/dbSpec.js#L171
• https://github.com/vitaly-t/pg-promise/blob/master/test/dbSpec.js#L17

When there is a connection-related error, your event error will have property cn set on the context parameter. On the context object.

You can also see how this works in action, if you use pg-monitor. Here's an example.

By the way, calling this:

var db = pgp("postgres://this:is/just:999/silly");

doesn't try to open a connection. You would have to call db.connect() to make it open the connection, if this is what you want to test.

[vitaly-t]

Here's a complete application for testing an invalid connection:

var options = {
    error: function (error, e) {
        if (e.cn) {
            // A connection-related error;
            console.log("CN:", e.cn);
            console.log("EVENT:", error.message);
        }
    }
};

var pgp = require("pg-promise")(options);

var db = pgp('invalid connection string');

db.connect()
    .then(function (obj) {
        obj.done(); // success, release connection;
    })
    .catch(function (error) {
        console.log("ERROR:", error.message);
    });

You would see that the same error is reported within .catch and event error. In the event you also get e.cn - secure connection details (with password hashed, if present).

For me it outputs:

CN: invalid connection string
EVENT: password authentication failed for user "Vitaly"
ERROR: password authentication failed for user "Vitaly"

[reinvantveer]

Yes, I'm seeing it thrown. Thanks for the elaborate answer and example!

[vitaly-t]

You are welcome!

See my latest meditation on the query performance: Performance Boost ;)

[vitaly-t]

Answer to the question was later elaborated here: Verify database connection with pg-promise when starting an app

[reinvantveer]

Thanks!

Den mån 21 mar 2016 06:35Vitaly Tomilov [email protected] skrev:

Answer to the question was later elaborated here:
http://stackoverflow.com/questions/36120435/how-to-ensure-database-connection-before-starting-app-server-with-pg-promise

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