db4o学习笔记(二)
更新对象
在Db4o数据库中更新对象很容易,例如:
Student template=new Student("Tom",0,null);
//得到要更新的对象
IObjectSet result=db.Get(template);
foreach(object item in result)
{
Student found=(Student)item;
found.Age+=10;
//更新对象到数据库
db.Set(found);
Console.WriteLine("Updated {0}",found);
}
GetAllStudent(db);
删除对象
在Db4o数据库中删除对象使用Delete方法,例如:
Student template=new Student("Tom",0,null);
//得到要删除的对象
IObjectSet result=db.Get(template);
foreach(object item in result)
{
Student found=(Student)item;
//删除对象
db.Delete(found);
Console.WriteLine("Deleted {0}",found);
}
GetAllStudent(db);
当对象的数据成员也是一个对象时,我们如何操作他们呢。db4o引入了更新深度(update depth)的概念来控制被更新的对象成员树深度。默认的更新深度是 1。
在前面的定义的学生类里有一个myschool数据成员,他是一个学校类,定义如下:
//定义一个学校类
public class School
{
private string name;
private string address;
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
public School()
{
//
// TODO: 在此处添加构造函数逻辑
//
}
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public School(string name,string address)
{
this.name=name;
this.address=address;
}
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public string Name
{
get
{
return name;
}
set
{
name=value;
}
}
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public string Address
{
get
{
return address;
}
set
{
address=value;
}
}
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public override string ToString()
{
return string.Format("name:{0};address:{1}",name,address);
}
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}
使用CascadeOnUpdate方法,可以更新成员对象,该方法必须在每次开启数据库之前设置.例如:
Db4oFactory.Configure().ObjectClass(typeof(Student)).CascadeOnUpdate(true);
IObjectContainer db=Db4oFactory.OpenFile("Student.yap");
try
{
Student template=new Student("Tom",0,null);
//得到要更新的对象
IObjectSet result=db.Get(template);
foreach(object item in result)
{
Student found=(Student)item;
found.Age+=10;
//更新学校对象
found.MySchool.Address="CHINA ANHUI";
//更新对象到数据库
db.Set(found);
Console.WriteLine("Updated {0}",found);
}
GetAllStudent(db);
}
finally
{
db.Close();
}
和CascadeOnUpdate方法一样,CascadeOnDelete方法用来删除所有对象.例如:
Db4oFactory.Configure().ObjectClass(typeof(Student)).CascadeOnDelete(true);
IObjectContainer db=Db4oFactory.OpenFile("Student.yap");
try
{
Student template=new Student("Tom",0,null);
//得到要删除的对象
IObjectSet result=db.Get(template);
foreach(object item in result)
{
Student found=(Student)item;
//删除对象
db.Delete(found);
Console.WriteLine("Deleted {0}",found);
}
GetAllStudent(db);
}
finally
{
db.Close();
}
在Db4o数据库中更新对象很容易,例如:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
删除对象
在Db4o数据库中删除对象使用Delete方法,例如:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
当对象的数据成员也是一个对象时,我们如何操作他们呢。db4o引入了更新深度(update depth)的概念来控制被更新的对象成员树深度。默认的更新深度是 1。
在前面的定义的学生类里有一个myschool数据成员,他是一个学校类,定义如下:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
使用CascadeOnUpdate方法,可以更新成员对象,该方法必须在每次开启数据库之前设置.例如:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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和CascadeOnUpdate方法一样,CascadeOnDelete方法用来删除所有对象.例如:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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