Represent a single-rowed table in EF? - entity-framework

Question

I have a configuration table in my database and it contains exactly one row.
ConfirmedScheduleColor | OverlappedScheduleColor | ColN
Currently, I'm retrieving the configuration like this:
var db = new SchedulingDbContext();
var config = db.Configurations.FirstOrDefault();
It's currently working fine and I can access my configurations and all. The thing is, the code looks awkward since I'm accessing the Configurations DbSet as if it contains many records (FirstOrDefault()); although actually, it contains only one record. I want to access my configurations like I'm accessing a static object. How to do that in EF?

Answer 1

You could simply add a property to your DbContext that returns Configurations.FirstOrDefault() and privatize the DbSet:
public class SchedulingDbContext : DbContext
{
private DbSet<Configuration> Configurations { get; set; }
public Configuration Configuration
{
get
{
return Configurations.FirstOrDefault();
}
}
}

Answer 2

I have a class in my project that has static methods to retrieve config settings. I use the ConfigurationManager rather than the database, but you could adapt it to get the setting from wherever you are storing the value.
In my example I have written a GetFromDb method for you that takes a key as parameter but that is because if I was storing my config settings in the database I wouldn't want to add a column every time I needed a new config setting. I would have a table with Key/Value columns. If you are wedded to the single row table then you might want to do without such a method.
public class Config
{
private _ConfirmedScheduleColor;
public static string ConfirmedScheduleColor
{
get
{
if(_ConfirmedScheduleColor == null)
_ConfirmedScheduleColor = GetFromDb("ConfirmedScheduleColor");
return _ConfirmedScheduleColor;
}
}
public static string OverlappedScheduleColor
{
get { return GetValue("OverlappedScheduleColor", "Pink"); }
}
public static int ColN
{
get { return GetValue("ColN", 2); }
}
private static string GetFromDb(string key)
{
if(key == "ConfirmedScheduleColor")
{
var config = db.Configurations.FirstOrDefault();
return config.ConfirmedScheduleColor;
}
}
private static string GetValue(string key, string defaultValue)
{
return ConfigurationManager.AppSettings[key] ?? defaultValue;
}
private static string GetValue(string key, int defaultValue)
{
int i;
if(int.TryParse(ConfigurationManager.AppSettings[key], out i))
return i;
return defaultValue;
}
}

Answer 3

In EF Core you can set the check constraint for the primary key. It enforces that column Id must have value that is equal to 1 which means only one record can exist in table if you have the primary key.
modelBuilder.Entity<YourTable>(e =>
{
e.HasCheckConstraint("CK_Table_Column", "[Id] = 1");
e.HasData(...) //optionally add some initial date for Id = 1
});