db4o是面向对象的数据库，复杂应用就不说了，说点简单的。
数据库嘛，简单的操作就是添加，删除，更新和查询。
1、添加添加非常简单：
先建一个需要存储的对象
Code
public class Model
{
public int ID { get; set; }
public string Name { get; set; }
public override string ToString()
{
return string.Format("ID:{0} , Name:{1}", ID, Name);
}
}
在进行存储操作
Code
using (IObjectContainer db = Db4oFactory.OpenFile("d:\\d.dat"))
{
db.Store(new Model() { ID = 1, Name = "Test" });
}
或者
Code
IObjectContainer db = Db4oFactory.OpenFile("d:\\d.dat");
db.Store(new Model() { ID = 1, Name = "Test" });
db.Dispose();
2、更新更新操作就有一个引用的概念。怎么确定是删除的对象，在db4o中是通过ObjectRefence来操作的。对象的指向一定要正确啦。所以虽然也是用Store方法进行更新操作，但是，不能直接更新。比如对于上面添加的一条记录使用
Code
IObjectContainer db = Db4oFactory.OpenFile("d:\\d.dat");
db.Store(new Model() { ID = 1, Name = "Test" });
db.Dispose();
并不会更新，而是一个添加操作。而下面的操作也无法更新：
Code
using (IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName))
{
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
db.Store(new Model() { ID = 1, Name = "Test2" });
}
}
需要更新引用才可以。因此要写成：
Code
using (IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName))
{
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
((Model)list[i]).Name = "Test2";
db.Store(list[i]);
}
}
在循环中list是无法直接赋值的。不能像下面那样用：
Code
using (IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName))
{
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
list[i] = new Model() { Name = "tttttt", ID = 2 };
db.Store(list[i]);
}
}
可以给Model对象添加一个方法：
Code
public class Model
{
public int ID { get; set; }
public string Name { get; set; }
public void SetValue(Model model)
{
this.ID = model.ID;
this.Name = model.Name;
}
public override string ToString()
{
return string.Format("ID:{0} , Name:{1}", ID, Name);
}
}
然后使用：
Code
using (IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName))
{
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
((Model)list[i]).SetValue(new Model() { Name = "tttttt", ID = 2 });
db.Store(list[i]);
}
}
当然，也可以像下面一样用：
Code
IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName);
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
((Model)list[i]).SetValue(new Model() { Name = "tttttt", ID = 2 });
db.Store(list[i]);
}
db.Dispose();
3、删除删除和更新差不多，也需要删除引用，可以有下面两种用法。
Code
using (IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName))
{
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
db.Delete(list[i]);
}
}
或者
Code
IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName);
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
db.Delete(list[i]);
}
db.Dispose();
4、查询更新和删除实际上已经用了查询，查询语句可以写成：
Code
using (IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName))
{
IObjectSet list = db.QueryByExample(new Model() { ID = 2 });
for (int i = 0; i < list.Count; i++)
{
Console.WriteLine(((Model)list[i]).ToString());
}
}
或者
Code
IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName);
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
for (int i = 0; i < list.Count; i++)
{
Console.WriteLine(list[i].ToString());
}
db.Dispose();
上面是根据对象查的。下面根据是按类型，用到的方法是Query。
Code
IObjectContainer db = Db4oFactory.OpenFile(Util.YapFileName);
IList<Model> list = db.Query<Model>(typeof(Model));
for (int i = 0; i < list.Count; i++)
{
Console.WriteLine(list[i].ToString());
}
db.Dispose();
把所有的Model类型的数据都查询出来了就。
5、简单讲解查询的时候，比如
Code
IObjectSet list = db.QueryByExample(new Model() { ID = 1 });
是查找所有ID为1的Model类型的数据。
如果要查找Name为“123”就写成：
Code
IObjectSet list = db.QueryByExample(new Model() { Name = "123" });
6、封装下面给两个操作的封装类：
对象封装
Code
public class Db4oHelper : IDisposable
{
IObjectContainer db;
public Db4oHelper(string fileName)
{
try
{
db = Db4oFactory.OpenFile(fileName);
}
catch { }
}
private bool IsOpened
{
get
{
if (db == null)
return false;
return true;
}
}
/// <summary>
/// 添加数据
/// </summary>
/// <param name="o">添加对象</param>
public void Set(object o)
{
if (IsOpened)
{
db.Store(o);
}
}
/// <summary>
/// 按类型检索全部
/// </summary>
/// <typeparam name="T">检索类型</typeparam>
/// <returns>返回类型列表</returns>
public IList<T> Find<T>()
{
if (IsOpened)
{
IList<T> list = db.Query<T>(typeof(T));
return list;
}
return null;
}
public List<T> Find<T>(object obj)
{
if (IsOpened)
{
IObjectSet list = db.QueryByExample(obj);
List<T> result = new List<T>(list.Count);
for (int i = 0; i < list.Count; i++)
{
result.Add((T)list[i]);
}
return result;
}
return null;
}
public IObjectSet Find(object obj)
{
if (IsOpened)
{
IObjectSet list = db.QueryByExample(obj);
return list;
}
return null;
}
/// <summary>
/// 删除对象
/// </summary>
/// <param name="o">删除条件，按属性删除，1-N个</param>
public void Delete(object o)
{
if (IsOpened)
{
IObjectSet list = Find(o);
for (int i = 0; i < list.Count; i++)
{
db.Delete(list[i]);
}
}
}
#region IDisposable 成员
public void Dispose()
{
if (IsOpened)
{
db.Close();
db.Dispose();
db = null;
}
}
#endregion
}
或者
静态方法封装
Code
public abstract class Db4oHelper2
{
private static readonly string fileName = "d:\\d.dat";
public static void Set(object o)
{
using (IObjectContainer db = Db4oFactory.OpenFile(fileName))
{
db.Store(o);
}
}
public static IList<T> Find<T>()
{
using (IObjectContainer db = Db4oFactory.OpenFile(fileName))
{
IList<T> list = db.Query<T>(typeof(T));
return list;
}
}
public static List<T> Find<T>(object o)
{
using (IObjectContainer db = Db4oFactory.OpenFile(fileName))
{
IObjectSet list = db.QueryByExample(o);
List<T> result = new List<T>(list.Count);
for (int i = 0; i < list.Count; i++)
{
result.Add((T)list[i]);
}
return result;
}
}
public static void Delete(object o)
{
using (IObjectContainer db = Db4oFactory.OpenFile(fileName))
{
IObjectSet list = db.QueryByExample(o);
for (int i = 0; i < list.Count; i++)
{
db.Delete(list[i]);
}
}
}
注意，以上两个封装并没有封装更新的方法，更新的时候需要新查询数据然后再更新。
（文/birdshover 出处/博客园）
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