db4objects 7.4应用笔记

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

    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

            using (IObjectContainer db = Db4oFactory.OpenFile("d:\\d.dat"))
            {
                db.Store(new Model() { ID = 1, Name = "Test" });
            }

或者

            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

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：

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：

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[i]是无法直接赋值的。不能像下面那样用：

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：

    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：

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：

    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。

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

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：

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

 

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。

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

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：

IObjectSet list = db.QueryByExample(new Model() { Name = "123" });

6、封装

下面给两个操作的封装类：

    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

   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。