We are designing our new product, which will include multi-tenancy. It will be written in ASP.NET and C#, and may be hosted on Windows Azure or some other Cloud hosting solution.
We’ve been looking at MVC and other technologies and, to be honest, we’re getting bogged down in various acronyms (MVC, EF, WCF etc. etc.).
A particular requirement of our application is causing a headache – the users will be able to add fields to the database, or even create a whole new module.
As a result, each tenant would have a database with a different structure to every other tenant using the system. We envisage that every tenant will have their own database, rather than sharing a database.
(Adding fields etc. to the system will be accomplished using a web interface).
All well and good, but the problem comes when creating a data model for MVC. Modifying a data model programmatically to add a field to a table seems to be impossible, according to this link:
This is a major headache for us. Even if we don’t use MVC, I think we’d still want to create a data model (perhaps for used with LINQ to SQL).
We’re considering having a table with loads of fields in it, and instead of adding fields to the database we allocate an existing field in the table when the user wants to add a field to his form. Not sure I like that idea, though.
Of course, we don’t have to use MVC or Entity Framework, but it appears to me that these are the kind of technologies that Microsoft would steer us towards for future development.
Any thoughts? I’m assuming that we’re not the first people in the world to consider this idea of a user-customisable application.
I’d make sure that you have fully explored the option of creating ‘Name-Value Pair’ type tables as described here http://msdn.microsoft.com/en-us/library/aa479086.aspx#mlttntda_nvp
before you start looking at a customizable schema. Also don’t forget that you are going to have to grant much higher permissions to your sql accounts in order for them to create tables on the fly.
A customizable schema means that your sql accounts will also need much higher permissions. It wouldnt be advisable to assign these higher permissions to a tenants account, but to a separate provisioning account which can perform these tasks.
Also before investing effort into EF – try googling ‘EF Vote of No Confidence’. It was raised (i believe) mainly in reaction to earlier versions but its definately worth reading up on. nHibernate is an alternative worth investigating.