Entity Framework 6 Code first Default value

Question

is there "elegant" way to give specific property a default value ?

Maybe by DataAnnotations, something like :

[DefaultValue("true")]
public bool Active { get; set; }

Thank you.

Answer 1

Hmm... I do DB first, and in that case, this is actually a lot easier. EF6 right? Just open your model, right click on the column you want to set a default for, choose properties, and you will see a "DefaultValue" field. Just fill that out and save. It will set up the code for you.

Your mileage may vary on code first though, I haven't worked with that.

The problem with a lot of other solutions, is that while they may work initially, as soon as you rebuild the model, it will throw out any custom code you inserted into the machine-generated file.

This method works by adding an extra property to the edmx file:

<EntityType Name="Thingy">
  <Property Name="Iteration" Type="Int32" Nullable="false" **DefaultValue="1"** />

And by adding the necessary code to the constructor:

public Thingy()
{
  this.Iteration = 1;

Answer 2

After @SedatKapanoglu comment, I am adding all my approach that works, because he was right, just using the fluent API does not work.

1- Create custom code generator and override Generate for a ColumnModel.

   public class ExtendedMigrationCodeGenerator : CSharpMigrationCodeGenerator
{

    protected override void Generate(ColumnModel column, IndentedTextWriter writer, bool emitName = false)
    {

        if (column.Annotations.Keys.Contains("Default"))
        {
            var value = Convert.ChangeType(column.Annotations["Default"].NewValue, column.ClrDefaultValue.GetType());
            column.DefaultValue = value;
        }


        base.Generate(column, writer, emitName);
    }

}

2- Assign the new code generator:

public sealed class Configuration : DbMigrationsConfiguration<Data.Context.EfSqlDbContext>
{
    public Configuration()
    {
        CodeGenerator = new ExtendedMigrationCodeGenerator();
        AutomaticMigrationsEnabled = false;
    }
}

3- Use fluent api to created the Annotation:

public static void Configure(DbModelBuilder builder){    
builder.Entity<Company>().Property(c => c.Status).HasColumnAnnotation("Default", 0);            
}

Answer 3

Your model properties don't have to be 'auto properties' Even though that is easier. And the DefaultValue attribute is really only informative metadata The answer accepted here is one alternative to the constructor approach.

public class Track
{

    private const int DEFAULT_LENGTH = 400;
    private int _length = DEFAULT_LENGTH;
    [DefaultValue(DEFAULT_LENGTH)]
    public int LengthInMeters {
        get { return _length; }
        set { _length = value; }
    }
}

vs.

public class Track
{
    public Track()
    {
        LengthInMeters = 400;   
    }

    public int LengthInMeters { get; set; }        
}

This will only work for applications creating and consuming data using this specific class. Usually this isn't a problem if data access code is centralized. To update the value across all applications you need to configure the datasource to set a default value. Devi's answer shows how it can be done using migrations, sql, or whatever language your data source speaks.

Answer 4

I admit that my approach escapes the whole "Code First" approach. But if you have the ability to just change the default value in the table itself... it's much simpler than the lengths that you have to go through above... I'm just too lazy to do all that work!

It almost seems as if the posters original idea would work:

[DefaultValue(true)]
public bool IsAdmin { get; set; }

I thought they just made the mistake of adding quotes... but alas no such intuitiveness. The other suggestions were just too much for me (granted I have the privileges needed to go into the table and make the changes... where not very developer will in every situation). In the end I just did it the old fashioned way. I set the default value in the SQL Server table... I mean really, enough already! NOTE: I further tested doing an add-migration and update-database and the changes stuck.

Answer 5

I don't know where are coming from these answers!

Lets consider you have a class name named Products and you have a IsActive field. just you need a create constructor :

Public class Products
{
    public Products()
    {
       IsActive = true;
    }
 public string Field1 { get; set; }
 public string Field2 { get; set; }
 public bool IsActive { get; set; }
}

Then your IsActive default value is True!

Edite :

if you want to do this with SQL use this command :

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .Property(b => b.IsActive)
        .HasDefaultValueSql("true");
}

Answer 6

It's been a while, but leaving a note for others. I achieved what is needed with an attribute and I decorated my model class fields with that attribute as I want.

[SqlDefaultValue(DefaultValue = "getutcdate()")]
public DateTime CreatedDateUtc { get; set; }

Got the help of these 2 articles:

• EF on CodePlex
• Andy Mehalick blog

What I did:

Define Attribute

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class SqlDefaultValueAttribute : Attribute
{
    public string DefaultValue { get; set; }
}

In the "OnModelCreating" of the context

modelBuilder.Conventions.Add( new AttributeToColumnAnnotationConvention<SqlDefaultValueAttribute, string>("SqlDefaultValue", (p, attributes) => attributes.Single().DefaultValue));

In the custom SqlGenerator

private void SetAnnotatedColumn(ColumnModel col)
{
    AnnotationValues values;
    if (col.Annotations.TryGetValue("SqlDefaultValue", out values))
    {
         col.DefaultValueSql = (string)values.NewValue;
    }
}

Then in the Migration Configuration constructor, register the custom SQL generator.

SetSqlGenerator("System.Data.SqlClient", new HarmonyMigrationSqlGenerator());