Question

I’m having a hard time trying to create a XmlRepository. The problem here I have the only choice to do this using XmlSerializer.

Please, check it out. It really a mess my code and frustrating. I wanna know how can I improve this code, I was thinking in creating a singleton but I’m not sure how to continue.

 public interface IRepository<T>
    where T : class
{
    T GetById(object id);
    IEnumerable<T> All();
    void Insert(T entity);
    void Remove(T entity);
    void SaveChanges();
} 

public class XmlRepository : IRepository<Configuration>
{
    public XmlRepository(string filename)
    {
        FileName = filename;
    }

    public XmlRepository(string filename)
    {
        FileName = filename;
    }

    internal string FileName { get; private set; }

    private Configuration GetById(object id)
    {
        throw new NotImplementedException();
    }

    public IEnumerable<Configuration> All()
    {
        return Get();
    }

    public void Insert(Configuration entity)
    {
        var configurations = Get();
        configurations.Add(entity);
        Save(configurations);
    }

    public void Remove(Configuration entity)
    {
        var configurations = Get();
        configurations.Remove(entity);
        Save(configurations);
    }

    private List<Configuration> Get()
    {
        try
        {
            XmlSerializer serializer = new XmlSerializer(typeof(List<Configuration>), null, new Type[] { typeof(BinaryConfiguration) }, new XmlRootAttribute("Configurations"), "http://ofimbres.wordpress.com/");
            StreamReader myWriter = new StreamReader(FileName);
            var list = serializer.Deserialize(myWriter);
            myWriter.Close();

            return (List<Configuration>)list;
        }
        catch (InvalidOperationException ex)
        {
            throw ex;
        }
    }

    public void Save(object configurations)
    {
        try
        {
            XmlSerializer serializer = new XmlSerializer(configurations.GetType(), null, new Type[] { typeof(BinaryConfiguration) }, new XmlRootAttribute("Configurations"), "http://ofimbres.wordpress.com/");
            StreamWriter myWriter = new StreamWriter(FileName);
            serializer.Serialize(myWriter, configurations);
            myWriter.Close();
        }
        catch (XmlException ex)
        {
            throw ex;
        } 
    }
}

Any doubt, please let me know.
Thanks a lot

Answer 1

Instead of reading and writing the file every time you call the repository, I would do the following:

In the constructor you read the file into a list of Configuration objects. Just like you do in the Get method at the moment. You save this list in a field of the class and use it for all the other methods (add, etc.).

Your repository does have a SaveChanges method, so this is the ideal place to serialize the configuration back to disk.

This should be a lot more performant than the current approach, less complex and therefore also less error-prone.

Edit: Here is a start:

public class XmlRepository : IRepository<Configuration>
{
    private readonly List<Configuration> configurations;

    public XmlRepository(string filename)
    {
        FileName = filename;

        XmlSerializer serializer = new XmlSerializer(typeof(List<Configuration>), null, new Type[] { typeof(BinaryConfiguration) }, new XmlRootAttribute("Configurations"), "http://ofimbres.wordpress.com/");
        using (StreamReader myWriter = new StreamReader(FileName))
        {
            configurations = (List<Configuration>)serializer.Deserialize(myWriter);
            myWriter.Close();
        }
    }

    internal string FileName { get; private set; }

    public Configuration GetById(object id)
    {
        return (from c in configurations where c.Id == id select c).Single();
    }

    public IEnumerable<Configuration> All()
    {
        return configurations;
    }

    public void Insert(Configuration entity)
    {
        configurations.Add(entity);
    }

    public void Remove(Configuration entity)
    {
        configurations.Remove(entity);
    }

    public void SaveChanges()
    {
        XmlSerializer serializer = new XmlSerializer(configurations.GetType(), null, new Type[] { typeof(BinaryConfiguration) }, new XmlRootAttribute("Configurations"), "http://ofimbres.wordpress.com/");
        using (StreamWriter myWriter = new StreamWriter(FileName))
        {
            serializer.Serialize(myWriter, configurations);
            myWriter.Close();
        }
    }
}

Also some general suggestions

• Use using for handling files/streams and other resources which needs to be disposed (StreamReader and StreamWriter in this case). This guarantees that the file will be closed even when there is an exception.
• Don’t catch and rethrow exceptions or if you do it, at least use throw instead of throw ex to preserve the full stack trace.

Hope this helps!