What's the likelihood of Orchard CMS running on postgresql database?

And if that is not possible, what are the implications of using SQL Ex开发者_JS百科press? Would there be anything wrong with using SQLExpress for the CMS db, and postgresql for my app?

Orchard does use NHibernate under the bonnet (http://www.orchardproject.net/docs/Orchard-dependencies-and-libraries.ashx), however the orchard web platform installer only allows you to choose between the sql compact database or a SQL Server instance (including express) -

see http://www.orchardproject.net/docs/Installing-Orchard.ashx

So out of the box at the moment no but as Raymond points out you can always write your own provider and contribute it to the Orchard project. (Check out this forum response to mysql - http://orchard.codeplex.com/Thread/View.aspx?ThreadId=229968).

NHibernate is the ORM that Orchard is using to access the database. NHibernate supports postgresql so the answer is yes. And ofcourse you can also write your own dataaccess layer that services access.

A few months after this question was asked, Marek Habersack added Mono support to Orchard. Part of that effort was adding support for running Orchard on PostgreSQL.

The patches for this must have been accepted as the current instructions for running Orchard on Mono do not require them to be added.

There were problems, at least initially, with the connection being dropped but there are reports of it running well.

I am not deeply familiar with this particular product, but unless they explicitly state that they support a certain SQL implementation, the chances are extremely slim that it would just happen to work. A quick look around their site suggests that you will need to use Microsoft's SQL Server.