C# string Formatting based on Model Attribute Annotation

Question

I'm working on a ".dat" file creation project, where the requirement is to generate a file with the necessary padding "zeros" or "spaces" for all the string values.

For example: I have a Class as below and the requirement is while generating a File using this model, file content should be 7 characters in length and anything below that should be replaced with "0" character .

public class Header
{
     // String length of 7, append "0" for leftover spaces.
     public string RECORD_TYPE { get;set;};
}

By considering the requirement above, if I set a Value to this Field as "ABC" (ie 3 characters in length) then it should be converted as "ABC0000" while generating a File to fulfill the 7 characters requirement .

To achieve this, I created a Custom Attribute as below:

public interface IFormatterAttribute
{
    string Format(string toFormat);
}

[AttributeUsage(AttributeTargets.All)]
public class PaddedLengthAttribute : Attribute, IFormatterAttribute
{
    private readonly int _length;
    private readonly char _paddingChar;
    private readonly PaddingDirection _paddingDirection;

    public PaddedLengthAttribute(int length, char paddingChar = '0', PaddingDirection direction = PaddingDirection.Right)
    {
        _length = length;
        _paddingChar = paddingChar;
        _paddingDirection = direction;
    }

    public string Format(string toFormat)
    {
        return _paddingDirection switch
        {
            PaddingDirection.Left => toFormat.PadLeft(_length, _paddingChar),
            PaddingDirection.Right => toFormat.PadRight(_length, _paddingChar),
            _ => toFormat.PadRight(_length, _paddingChar),
        };
    }

    public enum PaddingDirection
    {
        Left,
        Right
    }
}

So that, I can decorate Field using this custom attribute below:

[PaddedLengthAttribute(7,'0')]
public class Header
{
     // String length of 7, append "0" for leftover spaces.
     public string RECORD_TYPE { get;set;};
}

I need help here to understand the better approach of calling Format method of PaddedLengthAttribute class dynamically for each attribute it assigned to.

Answer 1

You can use Reflection to iterate through the properties of your Header class and retrieve their attributes, and if the property has a PaddedLengthAttribute, you can use it to format the property value.

Here's an example:

public static class AttributeHelper
{
    public static void ApplyPaddingAttributes(Header header)
    {
        var headerType = header.GetType();
        var properties = headerType.GetProperties();
        foreach (var property in properties)
        {
            var attributes = property.GetCustomAttributes(typeof(PaddedLengthAttribute), false);
            if (attributes.Length > 0)
            {
                var value = (string)property.GetValue(header);
                var attribute = (PaddedLengthAttribute)attributes[0];
                property.SetValue(header, attribute.Format(value));
            }
        }
    }
}

And you can use it like this:

var header = new Header() { RECORD_TYPE = "ABC" };
AttributeHelper.ApplyPaddingAttributes(header);