Question

We have a database that has been deployed to various clients. We are currently introducing a optional new feature that, to be used, will require the customers who want the feature to have a new table added to the existing database.

As we are rolling out a new piece of software that will have to interact with versions of the database both with and without the new table (and as we don’t want 2 versions one for customers who have the new table and one for ones who don’t) we were wondering if it is possible to programmatically determine (with entity framework) whether a table exists in the database (I can try to access the table and have it throw a exception but was wondering if there was a built in function to do this)

Thanks

Edit: Given that people are telling me i should be using a config file not checking with EF can anyone give me guidence on how to check the config file with, for example, a custom data annotations for a mvc controller. Something like:

[Boolean(Properties.Settings.Default.TableExists)]
public class NamedController : Controller

Which throws a page not found if false?

Edit 2: With the Suggestions given by people to use the config settings i ended up with the following solution

App settings to set whether the table exists

<appSettings>
    <add key="tableExists" value="True"/>
</appSettings>

a custom data annotation to say whether to allow access to controller

[AuthoriseIfTableExistsIsTrue]
public class NamedController : Controller

the code for the custom authorise

public class AuthoriseIfTableExistsIsTrue : AuthorizeAttribute
{
    private readonly bool _tableExists;

    public AuthoriseIfTableExistsIsTrue()
    {
        _tableExists = string.Equals(bool.TrueString, ConfigurationManager.AppSettings["tableExists"], StringComparison.InvariantCultureIgnoreCase);
    }

    public AuthoriseIfTableExistsIsTrue(bool authorise)
    {
        _tableExists = authorise;
    }

    protected override bool AuthorizeCore(HttpContextBase httpContext)
    {
        if (_tableExists)
            return base.AuthorizeCore(httpContext);
        else
            throw new HttpException(404, "HTTP/1.1 404 Not Found");
    }
}

Thanks everyone for the help and telling me not to use EF for this and use config setting instead

Answer 1

A much better option would be to store the version differences as configuration. This could be stored in the database itself, a configuration file or even web.config.

Otherwise you’ll end up with messy code like:

int result = entity.ExecuteStoreQuery<int>(@"
    IF EXISTS (SELECT * FROM sys.tables WHERE name = 'TableName') 
        SELECT 1
    ELSE
        SELECT 0
    ").SingleOrDefault();