Is it possible to add value constraints for string property via Entity Framework?

Question

I'm implementing user's language setting to store it in database:

[Table("User")]
public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public string Language { get; set; }

    [NotMapped]
    public CultureInfo Culture => string.IsNullOrWhiteSpace(Language) ? Thread.CurrentThread.CurrentCulture : new CultureInfo(Language);
}

Is it possible to specify Language values can be? For example: "sl-SI" or "hr-HR" or "ru-RU" only? Thanks in advance!

Emad · Accepted Answer · 2016-11-15 07:02:45Z

3

Maybe you can create an enum of supported languages and use helper for strings:

public enum SupportedLanguages
{
    [Description("sl-SL")]
    Sl,
    [Description("hr-HR")]
    Hr,
    [Description("ru-RU")]
    Ru
}

public static string GetDescription(this Enum value)
{            
    FieldInfo field = value.GetType().GetField(value.ToString());

    DescriptionAttribute attribute
            = Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute))
                as DescriptionAttribute;

    return attribute == null ? value.ToString() : attribute.Description;
}

Then use this like this

[Table("User")]
public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    private SupportedLanguages language;
    public SupportedLanguages Language 
    { 
        get { return language; }
        set 
        {
            if(!Enum.IsDefined(typeof(SupportedLanguages), value))
                throw new ArgumentOutOfRangeException();
            language = value;
        }
    }

    [NotMapped]
    public CultureInfo Culture => string.IsNullOrWhiteSpace(Language.GetDescription()) ? Thread.CurrentThread.CurrentCulture : new CultureInfo(Language.GetDescription());
}

edited Nov 15, 2016 at 7:02

answered Nov 15, 2016 at 5:51

Emad

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8 Comments

Slava Utesinov Over a year ago

What about ctx.Database.ExecuteSqlCommand("insert into Users(Language) values (22)") and user.Language = (SupportedLanguages)22?

Slava Utesinov Over a year ago

Are you sure, you can try it by yourself

Emad Over a year ago

You can't assign an invalid integer value to a enum field. The whole idea behind enum is this. Also you can invalidate database in many ways manually but if you use EF all the way you don't need to worry about it

Emad Over a year ago

@SlavaUtesinov Sure I forgot that in C# enums are not checked! and it's for Flags capability. I have edited the answer see the new one.

user3818229 Over a year ago

Improving my code I think it would be better to make SupportedLanguages property required and remove extra validation from get method of Culture property.

|

Slava Utesinov · Accepted Answer · 2016-11-15 06:31:45Z

0

You should do it at migration:

public override void Up()
{  
    Sql("ALTER TABLE Users ADD CONSTRAINT LanguageCnst CHECK (Language in ('sl-SI', 'hr-HR', 'ru-RU'))");
}

public override void Down()
{
    Sql('ALTER TABLE Users DROP CONSTRAINT LanguageCnst');
}

And add some code to User:

[Table("User")]
public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public string Language { get; protected set; }

    public setLanguage(string value)
    {
        if(new[]{"sl-SI", "hr-HR", "ru-RU"}.Contains(value))
            Language = value;
    }

    [NotMapped]
    public CultureInfo Culture => string.IsNullOrWhiteSpace(Language) ? Thread.CurrentThread.CurrentCulture : new CultureInfo(Language);
}

edited Nov 15, 2016 at 6:31

answered Nov 15, 2016 at 5:51

Slava Utesinov

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