I have an XML document, several actually, that will be editable via a front-end UI. I've discovered a problem with this approach (other than the fact that it is using xml files instead of a database... but I cannot
change that right now).
If one user makes a
change while another user is in the process of making a
change, then the second one's changes will overwrite the first.
I need to be able to request objects from the xml files,
change them, and then submit the changes back to the xml file without re-writing the entire file. I've got my entire xml access class posted here (which was formed thanks to wonderful help from stackoverflow!)
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
namespace Repositories
{
/// <summary>
/// A file base repository represents a data backing that is stored in an .xml file.
/// </summary>
public partial class Repository<T> : IRepository
{
/// <summary>
/// Default constructor for a file repository
/// </summary>
public Repository() { }
/// <summary>
/// Initialize a basic repository with a filename. This will have to be passed from a context to be mapped.
/// </summary>
/// <param name="filename"></param>
public Repository(string filename)
{
FileName = filename;
}
/// <summary>
/// Discovers a single item from this repository.
/// </summary>
/// <typeparam name="TItem">The type of item to recover.</typeparam>
/// <typeparam name="TCollection">The collection the item belongs to.</typeparam>
/// <param name="expression"></param>
/// <returns></returns>
public TItem Single<TItem, TCollection>(Predicate<TItem> expression)
where TCollection : IDisposable, IEnumerable<TItem>
{
using (var list = List<TCollection>())
{
return list.Single(i => expression(i));
}
}
/// <summary>
/// Discovers a collection from the repository,
/// </summary>
/// <typeparam name="TCollection"></typeparam>
/// <returns></returns>
public TCollection List<TCollection>()
where TCollection : IDisposable
{
using (var list = System.Xml.Serializer.Deserialize<TCollection>(FileName))
{
return (TCollection)list;
}
}
/// <summary>
/// Discovers a single item from this repository.
/// </summary>
/// <typeparam name="TItem">The type of item to recover.</typeparam>
/// <typeparam name="TCollection">The collection the item belongs to.</typeparam>
/// <param name="expression"></param>
/// <returns></returns>
public List<TItem> Select<TItem, TCollection>(Predicate<TItem> expression)
where TCollection : IDisposable, IEnumerable<TItem>
{
using (var list = List<TCollection>())
{
return list.Where( i => expression(i) ).ToList<TItem>();
}
}
/// <summary>
/// Attempts to save an entire collection.
/// </summary>
/// <typeparam name="TCollection"></typeparam>
/// <param name="collection"></param>
/// <returns></returns>
public Boolean Save<TCollection>(TCollection collection)
{
try
{
// load the collection into an xml reader and try to serialize it.
System.Xml.XmlDocument xDoc = new System.Xml.XmlDocument();
xDoc.LoadXml(System.Xml.Serializer.Serialize<TCollection>(collection));
// attempt to flush the file
xDoc.Save(FileName);
// assume success
return true;
}
catch
{
return false;
}
}
internal string FileName { get; private set; }
}
public interface IRepository
{
TItem Single<TItem, TCollection>(Predicate<TItem> expression) where TCollection : IDisposable, IEnumerable<TItem>;
TCollection List<TCollection>() where TCollection : IDisposable;
List<TItem> Select<TItem, TCollection>(Predicate<TItem> expression) where TCollection : IDisposable, IEnumerable<TItem>;
Boolean Save<TCollection>(TCollection collection);
}
}
