This snippet demonstrates how to extend one of Sitefinity's classes (like Discount) to support dynamic fields.

DynamicTypes.cs

// If this class is not already setup as a dynamic meta type - set it up. Without this, you cannot add custom fields to the type
if (metaManager.GetMetaType(typeof(Discount)) == null)
{
    metaManager.CreateMetaType(typeof(Discount));
    metaManager.SaveChanges();
}

// The snippet below allows you to create a new property/field of the specified type (Discount). The benefit to this is that Sitefinity will actually create a new column for "Uses" and this can be saved/read using Sitefinity's functions: discountObject.GetValue<decimal>("Uses") and discountObject.SetValue("Uses", 1)

App.WorkWith()
    .DynamicData()
    .Type(typeof(Discount))
    .Field()
    .TryCreateNew("Uses", typeof(decimal)) // This line is what defines the field name and the type of the field. This also determines what column type is created in the database.
    .SaveChanges(true);