EF 7 set initial default value for DateTime column

You want to set the default value SQL, not a constant value:

entity.Property(e => e.ShipDate).HasDefaultValueSql("getutcdate()");

A more flexible solution using attributes for EF Core:

in your DbContext:

protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);
    // Add your customizations after calling base.OnModelCreating(builder);
    CustomDataTypeAttributeConvention.Apply(builder);
    DecimalPrecisionAttributeConvention.Apply(builder);
    SqlDefaultValueAttributeConvention.Apply(builder);
}

and create these classes:

public static class SqlDefaultValueAttributeConvention
{
    public static void Apply(ModelBuilder builder)
    {
        ConventionBehaviors
            .SetSqlValueForPropertiesWithAttribute<SqlDefaultValueAttribute>(builder, x => x.DefaultValue);
    }
}

public static class DecimalPrecisionAttributeConvention
{
    public static void Apply(ModelBuilder builder)
    {
        ConventionBehaviors
            .SetTypeForPropertiesWithAttribute<DecimalPrecisionAttribute>(builder,
                x => $"decimal({x.Precision}, {x.Scale})");
    }
}

public class CustomDataTypeAttributeConvention
{
    public static void Apply(ModelBuilder builder)
    {
        ConventionBehaviors
            .SetTypeForPropertiesWithAttribute<DataTypeAttribute>(builder,
                x => x.CustomDataType);
    }
}

public static class ConventionBehaviors
{
    public static void SetTypeForPropertiesWithAttribute<TAttribute>(ModelBuilder builder, Func<TAttribute, string> lambda) where TAttribute : class
    {
        SetPropertyValue<TAttribute>(builder).ForEach((x) => {
            x.Item1.Relational().ColumnType = lambda(x.Item2);
        });
    }

    public static void SetSqlValueForPropertiesWithAttribute<TAttribute>(ModelBuilder builder, Func<TAttribute, string> lambda) where TAttribute : class
    {
        SetPropertyValue<TAttribute>(builder).ForEach((x) =>
        {
            x.Item1.Relational().DefaultValueSql = lambda(x.Item2);
        });
    }

    private static List<Tuple<IMutableProperty, TAttribute>> SetPropertyValue<TAttribute>(ModelBuilder builder) where TAttribute : class
    {
        var propsToModify = new List<Tuple<IMutableProperty, TAttribute>>();
        foreach (var entity in builder.Model.GetEntityTypes())
        {
            var properties = entity.GetProperties();
            foreach (var property in properties)
            {
                var attribute = property.PropertyInfo
                    .GetCustomAttributes(typeof(TAttribute), false)
                    .FirstOrDefault() as TAttribute;
                if (attribute != null)
                {
                    propsToModify.Add(new Tuple<IMutableProperty, TAttribute>(property, attribute));
                }
            }
        }
        return propsToModify;
    }
}

and custom attributes:

/// <summary>
/// Set a default value defined on the sql server
/// </summary>
[AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
public class SqlDefaultValueAttribute : Attribute
{
    /// <summary>
    /// Default value to apply
    /// </summary>
    public string DefaultValue { get; set; }

    /// <summary>
    /// Set a default value defined on the sql server
    /// </summary>
    /// <param name="value">Default value to apply</param>
    public SqlDefaultValueAttribute(string value)
    {
        DefaultValue = value;
    }
}

/// <summary>
/// Set the decimal precision of a decimal sql data type
/// </summary>
[AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
public class DecimalPrecisionAttribute : Attribute
{
    /// <summary>
    /// Specify the precision - the number of digits both left and right of the decimal
    /// </summary>
    public int Precision { get; set; }

    /// <summary>
    /// Specify the scale - the number of digits to the right of the decimal
    /// </summary>
    public int Scale { get; set; }

    /// <summary>
    /// Set the decimal precision of a decimal sql data type
    /// </summary>
    /// <param name="precision">Specify the precision - the number of digits both left and right of the decimal</param>
    /// <param name="scale">Specify the scale - the number of digits to the right of the decimal</param>
    public DecimalPrecisionAttribute(int precision, int scale)
    {
        Precision = precision;
        Scale = scale;
    }

    public DecimalPrecisionAttribute(int[] values)
    {
        Precision = values[0];
        Scale = values[1];
    }
}

Then you will be able to decorate your table properties with any of these attributes (or make your own custom ones):

[DecimalPrecision(18, 9)] [SqlDefaultValue("getutcdate()")] [DataType("decimal(18,9)")]

@Michael Brown Thank you for these custom Attributes,

Update (EF Core 3.x): Starting with EF Core 3.0, the metadata API has changed again - Relational() extensions have been removed, and properties have been replaced with Get and Set extension methods, so now the code looks like this:

credit for @Ivan Stoev in this answer https://stackoverflow.com/a/42467710/1475257

so whole code from @Michael Brown in NET Core and .NET 5 will be

Convensions

    public static class DecimalPrecisionAttributeConvention
    {
        public static void Apply(ModelBuilder builder)
        {
            ConventionBehaviors
                .SetTypeForPropertiesWithAttribute<DecimalPrecisionAttribute>(builder,
                    x => $"decimal({x.Precision}, {x.Scale})");
        }
    }

    public class CustomDataTypeAttributeConvention
    {
        public static void Apply(ModelBuilder builder)
        {
            ConventionBehaviors
                .SetTypeForPropertiesWithAttribute<DataTypeAttribute>(builder,
                    x => x.CustomDataType);
        }
    }

    public static class ConventionBehaviors
    {
        public static void SetTypeForPropertiesWithAttribute<TAttribute>(ModelBuilder builder, Func<TAttribute, string> lambda) where TAttribute : class
        {
            SetPropertyValue<TAttribute>(builder).ForEach((x) =>
            {
                x.Item1.SetColumnType(lambda(x.Item2));
            });
        }

        public static void SetSqlValueForPropertiesWithAttribute<TAttribute>(ModelBuilder builder, Func<TAttribute, string> lambda) where TAttribute : class
        {
            SetPropertyValue<TAttribute>(builder).ForEach((x) =>
            {
                x.Item1.SetDefaultValueSql(lambda(x.Item2));
            });
        }

        private static List<Tuple<IMutableProperty, TAttribute>> SetPropertyValue<TAttribute>(ModelBuilder builder) where TAttribute : class
        {
            var propsToModify = new List<Tuple<IMutableProperty, TAttribute>>();
            foreach (var entity in builder.Model.GetEntityTypes())
            {
                var properties = entity.GetProperties();
                foreach (var property in properties)
                {
                    var attribute = property.PropertyInfo
                        .GetCustomAttributes(typeof(TAttribute), false)
                        .FirstOrDefault() as TAttribute;
                    if (attribute != null)
                    {
                        propsToModify.Add(new Tuple<IMutableProperty, TAttribute>(property, attribute));
                    }
                }
            }
            return propsToModify;
        }
    }

and Attributes

    /// <summary>
    /// Set a default value defined on the sql server
    /// </summary>
    [AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
    public class SqlDefaultValueAttribute : Attribute
    {
        /// <summary>
        /// Default value to apply
        /// </summary>
        public string DefaultValue { get; set; }

        /// <summary>
        /// Set a default value defined on the sql server
        /// </summary>
        /// <param name="value">Default value to apply</param>
        public SqlDefaultValueAttribute(string value)
        {
            DefaultValue = value;
        }
    }

    /// <summary>
    /// Set the decimal precision of a decimal sql data type
    /// </summary>
    [AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
    public class DecimalPrecisionAttribute : Attribute
    {
        /// <summary>
        /// Specify the precision - the number of digits both left and right of the decimal
        /// </summary>
        public int Precision { get; set; }

        /// <summary>
        /// Specify the scale - the number of digits to the right of the decimal
        /// </summary>
        public int Scale { get; set; }

        /// <summary>
        /// Set the decimal precision of a decimal sql data type
        /// </summary>
        /// <param name="precision">Specify the precision - the number of digits both left and right of the decimal</param>
        /// <param name="scale">Specify the scale - the number of digits to the right of the decimal</param>
        public DecimalPrecisionAttribute(int precision, int scale)
        {
            Precision = precision;
            Scale = scale;
        }

        public DecimalPrecisionAttribute(int[] values)
        {
            Precision = values[0];
            Scale = values[1];
        }
    }