added postConnectionQuery configuration

[yacoobk]

I needed to set client-connection defaults, specifically 'SET extra_float_digits = 3;' to run before any other SQL query. This fixes an issue with double precision values being truncated (which I reported to node-postgres a while ago but got no response for - Issue 730).

As a generic way to set any of these parameters, I figured the ability to specify a SQL query that runs once whenever a new connection is opened would be best. So I added a postConnectionQuery configuration option, and modified the adapter.spawnConnection function. I toyed with the idea of specifying a JSON object or array of parameters instead, but figured directly specifying a SQL string would be easier and more flexible.

Also I'm not entirely sure how best to unit test this. As I couldn't see any tests on spawnConnection I have not made new ones.

[tjwebb]

You could do this in a sails hook as well, by listening for hooks:orm:loaded. Or if you're just using waterline, you could run this query in the waterline.initialize callback.

[yacoobk]

Thanks for your suggestion. The client-connection default must be run on every opened database connection once before any regular sails model query is issued.

By default 10 connections to the postgres database are opened by node-postgres, and it manages connection pooling automatically. I was under the impression using the sails hook or waterline.initialise would issue the query only once, not on every postgres connection. Would that be the case? Also what would happen if a db connection is dropped and a new one established - how would the hooks or waterline approach you have suggested behave?

[particlebanana]

I'd rather see this supported at the node-pg level. This could come in handy when we get transactions added to set what the default level is but we can take a pass then. I would pressure the node-pg team if this is really an issue with the driver.