Self Formatting SQLish Filters... for the lazy

QueryFilterAttribute.cs

[AttributeUsage( AttributeTargets.Property )]
public class QueryFilterAttribute : Attribute {
	public QueryFilterAttribute( string fieldName )
	{
		FieldName = fieldName;
	}

	public QueryFilterAttribute() { }

	public string FieldName { get; }

	public string Format( PropertyInfo pi, object instance )
	{
		var value = pi.GetValue( instance );
		switch( value ) {
			case bool b: return $"{FieldName ?? pi.Name} = {b.ToString().ToLowerInvariant()}";
			case null: return null;
		}

		return null;
	}
}

QueryFilterFormatter.cs

public static class QueryFilterFormatter<T> {
	private static readonly (QueryFilterAttribute queryFilter, PropertyInfo pi)[] _info = typeof(T)
		.GetProperties( BindingFlags.Instance | BindingFlags.Public )
		.Select( x => (queryFilter: x.GetCustomAttribute<QueryFilterAttribute>(), pi: x) )
		.Where( x => x.queryFilter != null )
		.ToArray();

	public static string Format( T instance ) =>
		string.Join( " AND ", _info
			.Select( x => x.queryFilter.Format( x.pi, instance ) )
			.Where( x => x != null ) );
}

QueryParams.cs

public class QueryParams
{
	[QueryFilter("is_network_notification")]
	public bool? IsNetworkNotification { get; set; }

	[QueryFilter("is_published")]
	public bool? IsPublished { get; set; }

	[QueryFilter("is_test_account")]
	public bool? IsTestAccount { get; set; }

	public override string ToString() => QueryFilterFormatter<QueryParams>.Format(this);
}