有时候系统需要存储一些简单的关系型属性，不考虑并发，不考虑性能（一次操作在几ms），数据库没有其他依赖引用，拿过来就可以用
为什么选xml作为数据库？
可读性好
实体的对应关系不严格 ，
二进制序列化实体改动后不能读取以前序列化的数据，而且实体上面需要贴可序列化标签
数据库功能
无侵入存储实体，可存储poco对象，不需要在实体上面贴标签或继承什么
单例操作内存数据，只有初始化或者写入的时候才会读写文件，其他时候操作内存中的数据
使用指南
* 定义实体（public）
public class Friend{}
* 定义实体操作类，继承XmlDb<T>
public class FriendDbSet : XmlDb<Friend>
{
static FriendDbSet _instance = new FriendDbSet();
public static FriendDbSet GetInstance()
{
return _instance;
}
}
* 操作实体
Friend friend = new Friend() { Id = "1", name = "何仙姑" };
Friend friend2 = new Friend() { Id = "1", name = "何仙姑2" };
//添加
FriendDbSet.GetInstance().Add(friend2);
//删除
FriendDbSet.GetInstance().Remove(r => r.Id == "1");
//修改
friend.name = "何惠惠";
FriendDbSet.GetInstance().UpdateByIdOrKey(friend);
//查询
var result = FriendDbSet.GetInstance().ToList().Where(r => r.name.StartsWith("何"));
>也可以不定义实体操作类直接进行如下操作
>XmlDb<Friend>.GetInstance().Add(u);//增加
>XmlDb<Friend>.GetInstance().Remove(r=>r.Age>1000);//根据条件删除
>XmlDb<Friend>.GetInstance().Remove("key");//根据key或id删除
>XmlDb<Friend>.GetInstance().UpdateByIdOrKey(new User() { });//修改
>XmlDb<Friend>.GetInstance().ToList();//查询全部
>XmlDb<Friend>.GetInstance().Find("key");//查询单个
代码（使用单例模式，模版方法模式）
public class XmlDb where T : new()
{
private static XmlDb instance = new XmlDb();
public static XmlDb<T> GetInstance()
{
return instance;
}
private List<T> entityList = new List<T>();
public XmlDb()
{
this.SetDbFile();
this.ReadDb();
}
private string dbFile;
private string Dbfile
{
get { return dbFile; }
set
{
if (!string.IsNullOrEmpty(value) && !value.Equals(dbFile))
{
this.entityList.Clear();
}
dbFile = value;
this.ReadDb();
}
}
protected virtual void ReadDb()
{
if (File.Exists(this.Dbfile))
{
XmlSerializer ks = new XmlSerializer(typeof(List<T>));
Stream reader = new FileStream(this.Dbfile, FileMode.Open, FileAccess.ReadWrite);
this.entityList = ks.Deserialize(reader) as List<T>;
reader.Close();
}
else
{
this.entityList = new List<T>();
}
}
protected virtual void SetDbFile()
{
string folder = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "storage", "litedb");
if (!Directory.Exists(folder)) Directory.CreateDirectory(folder);
Type type = typeof(T);
if (string.IsNullOrEmpty(this.Dbfile))
{
//获取全名称签名，防止类名重复
string md5Sign = BitConverter.ToString(MD5.Create().ComputeHash(System.Text.Encoding.UTF8.GetBytes(type.FullName))).Replace("-", "");
this.Dbfile = Path.Combine(folder, type.Name + "_" + md5Sign + ".xml");
}
}
protected virtual void WriteDb()
{
//异常处理
string tempFileName = this.dbFile.Replace(".xml", "_Temp.xml");
try
{
XmlSerializer ks = new XmlSerializer(typeof(List<T>));
FileInfo fi = new FileInfo(this.Dbfile);
var dir = fi.Directory;
if (!dir.Exists)
{
dir.Create();
}
//缓存数据防止读写失败
if (fi.Exists)
{
fi.CopyTo(tempFileName, true);
}
Stream writer = new FileStream(this.Dbfile, FileMode.Create, FileAccess.ReadWrite);
ks.Serialize(writer, this.entityList);
writer.Close();
//删除缓存数据
if (File.Exists(tempFileName))
{
File.Delete(tempFileName);
}
UpdateSchema();
}
catch (Exception ex)
{
//恢复数据
throw ex;
}
}
/// <summary>
/// 更新数据的元数据信息
/// </summary>
private void UpdateSchema()
{
string root = Path.GetDirectoryName(this.Dbfile);
var files = Directory.GetFiles(root, "*.xml").Where(r => !r.EndsWith("schema.xml")).Select(r => Path.GetFileName(r));
//构建xml并存储
string schemaFile = Path.Combine(root, "schema.xml");
XDocument xdoc = new XDocument();
XElement xmlroot = new XElement("root");
xdoc.Add(xmlroot);
foreach (var item in files)
{
xdoc.Root.Add(new XElement("fileName", item));
}
xdoc.Save(schemaFile);
}
/// <summary>
/// 根据主键或Id获取实体对象
/// </summary>
/// <param></param>
/// <returns></returns>
public T Find(string KeyOrId)
{
Type t = typeof(T);
foreach (var inst in this.entityList)
{
foreach (PropertyInfo pro in t.GetProperties())
{
var keyattr = pro.GetCustomAttribute(typeof(System.ComponentModel.DataAnnotations.KeyAttribute), false);
if (keyattr != null || pro.Name.ToLower() == "id")
{
if (pro.GetValue(inst, null)?.ToString() == KeyOrId)
{
return inst;
}
}
}
}
return default(T);
}
public void Add(T entity)
{
this.entityList.Add(entity);
this.WriteDb();
}
public void AddRange(List<T> list)
{
this.entityList.AddRange(list);
this.WriteDb();
}
public List<T> ToList()
{
this.ReadDb();
return entityList;
}
/// <summary>
/// 根据条件移除元素
/// </summary>
/// <param></param>
public void Remove(Predicate<T> filters)
{
this.entityList.RemoveAll(filters);
this.WriteDb();
}
/// <summary>
/// 根据key或id移除元素
/// </summary>
/// <param></param>
public void Remove(string KeyOrId)
{
Type t = typeof(T);
T entity = default(T);
foreach (var inst in this.entityList)
{
foreach (PropertyInfo pro in t.GetProperties())
{
var keyattr = pro.GetCustomAttribute(typeof(System.ComponentModel.DataAnnotations.KeyAttribute), false);
if (keyattr != null || pro.Name.ToLower() == "id")
{
if (pro.GetValue(inst, null)?.ToString() == KeyOrId)
{
entity = inst;
goto FinishLoop;
}
}
}
}
FinishLoop:
entityList.Remove(entity);
this.WriteDb();
}
public void UpdateByIdOrKey(T entity)
{
Type t = typeof(T);
string id = string.Empty;
foreach (PropertyInfo pro in t.GetProperties())
{
var keyattr = pro.GetCustomAttribute(typeof(System.ComponentModel.DataAnnotations.KeyAttribute), false);
if (keyattr != null || pro.Name.ToLower() == "id")
{
id = pro.GetValue(entity, null)?.ToString();
break;
}
}
this.Remove(id);
this.Add(entity);
}
/// <summary>
/// 清空列表
/// </summary>
/// <param></param>
public void Clear()
{
entityList.Clear();
this.WriteDb();
}
}
