Return query result state from PostgreSQL query in node.js

Question

I have a node.js server connected to a PostgreSQL database using the pg module. At one point I will insert data into two different database tables for a single HTTP POST . If the first query fails, the second should not be executed, but I have some trouble achieving this.

My generalized query function looks like this:

// General insertion function. If endResponse is true, the response will be ended,
// if it is false it will just write to the response and not end it (unless errors occurs).
function performInsertQuery(request, response, query, endResponse) {
    var pg = require('pg');

    var client = new pg.Client(request.app.get('postgreConnection'));
    client.connect(function(error) {
        if (error)
        {
            message = 'Could not connect to PostgreSQL database: ' + error;
            response.end(message);
            console.error(message);
            client.end();
        }
        else
        {            
            client.query(query, function (error, result)
            {
                if (error)
                {
                    var message = 'Error running query ' + query + ': ' + error;
                    response.writeHead(500, {'content-type':'application/json'});
                    response.end(message);
                    console.error(message);
                    client.end();
                }
                else
                {
                    var message = 'Query performed: ' + query;
                    if (endResponse)
                    {
                        response.end(message);
                    }
                    else
                    {
                        response.write(message + '\n');
                    }
                    console.log(message);
                    client.end();
                }

            });
        }
    });
}

Later, I have something like the following:

// query = some query
performInsertQuery(request, response, query, false);

// Stop running here if there was any errors running the query.

// Currently, this gets executed even though the first query fails.
// anotherQuery = another query
performInsertQuery(request, response, anotherQuery, true);

I have tried returning true and false from the function performInsertQuery , but since these are inner functions the result is not returned properly from the outer functions. Also, some if it is run asynchronously, which makes things a bit harder as well. I was not able to make it work with try/catch around the call to performInsertQuery either. I guess I could do another query to see if data was inserted, but this seems unnecessary and not very robust.

What would be the best way to return a success or failure state from performInsertQuery ?

Answer 1

I know this doesn't exactly handle your question as you intended(dealing with this entirely in node.js), but this sounds like an excellent usecase for a Postgres transaction....Do not commit results unless all insertions/updates are successful. SQL transactions are built for scenarios like yours.

Here are the docs and example code for it with your node module. https://github.com/brianc/node-postgres/wiki/Transactions

http://www.postgresql.org/docs/9.2/static/tutorial-transactions.html