Example of compound iteration when performing validation against loosely typed data

compounditeration.cs

public List<string> Validate(IDictionary<string, object> data, List<Field> mandatoryFields)
{
    var errors = new List<string>();
    
    foreach (var field in mandatoryFields)
    {
        if (!data.Keys.Contains(field.Identifier))
        {
            errors.add(String.Format("The {0} field is required", field.Identifier);
        }
    }
    
    return errors;
}