Change the default datatype for string

ModelBuilderExtensions.cs

       public static void SetDefaultDataType(this ModelBuilder modelBuilder)
        {
            foreach (var entity in modelBuilder.Model.GetEntityTypes().Where(x => x.ClrType.GetCustomAttribute(typeof(TableAttribute)) != null))
            {
                var entityClass = entity.ClrType;

                foreach (var property in entityClass.GetProperties().Where(p => p.PropertyType == typeof(string)
                                                                             && p.PropertyType.IsPublic && p.CanWrite
                                                                             && !Attribute.IsDefined(p, typeof(ColumnAttribute))
                                                                             && !Attribute.IsDefined(p, typeof(NotMappedAttribute))))
                {
                    var maxLength = "max";
                    if (Attribute.IsDefined(property, typeof(MaxLengthAttribute)))
                    {
                        maxLength = (property.GetCustomAttributes(typeof(MaxLengthAttribute), true).First() as MaxLengthAttribute).Length.ToString();
                    }
                    else if (Attribute.IsDefined(property, typeof(StringLengthAttribute)))
                    {
                        maxLength = (property.GetCustomAttributes(typeof(StringLengthAttribute), true).First() as StringLengthAttribute).MaximumLength.ToString();
                    }

                    modelBuilder.Entity(entityClass).Property(property.Name).HasColumnType($"varchar ({maxLength})");
                }
            }
        }