• [ActiveRecord]之 CRUD


    ActiveRecord 的 CRUD 操作基本上都是由 ActiveRecordBase 的静态方法完成。其实例(含子类型)方法,以及 ActiveRecordMediator 只是对这些静态方法的包装调用而已。当然,ActiveRecordBase 方法又是对 NHibernate Session 方法的包装。

    我们用下面这个实体来简单演示一下常用方法的使用。

    [ActiveRecord("Users")]
    public class User : ActiveRecordBase<User>
    {
      private int id;

      [PrimaryKey(PrimaryKeyType.Identity, Access=PropertyAccess.FieldCamelcase)]
      public int Id
      {
        get { return id; }
      }

      private string name;

      [Property(Unique=true, NotNull=true)]
      public string Name
      {
        get { return name; }
        set { name = value; }
      }
    }


    为了观察 NHibernate 生成的 SQL 语句,我们在配置文件中添加 "show_sql" 配置。

    <?xml version="1.0" encoding="utf-8" ?>
    <activerecord>
      <config>
        <add key="hibernate.connection.driver_class" value="NHibernate.Driver.SqlClientDriver" />
        <add key="hibernate.dialect" value="NHibernate.Dialect.MsSql2000Dialect" />
        <add key="hibernate.connection.provider" value="NHibernate.Connection.DriverConnectionProvider" />
        <add key="hibernate.connection.connection_string" value="server=(local);uid=sa;pwd=123456;database=test" />
        <add key="hibernate.show_sql" value="true" />
      </config>
    </activerecord>


    1. Create

    Create 通过调用 NHibernate.ISession.Save() 方法完成实体类型的存储操作。方法调用完成后,我们就能立即获取 PrimaryKey ID。

    User user = new User();
    user.Name = "User";
    user.Create();

    Console.WriteLine(user.Id);


    SQL

    NHibernate: INSERT INTO Users (Name) VALUES (@p0); select SCOPE_IDENTITY()
    @p0 = 'User'


    2. Update

    Update 通过调用 NHibernate.ISession.Update() 方法完成实体类型的更新操作。

    User user2 = User.Find(1);
    user2.Name = "User2";
    user2.Update();


    SQL

    NHibernate: SELECT user0_.Id as Id0_, user0_.Name as Name0_ FROM Users user0_ WHERE user0_.Id=@p0
    @p0 = '1'
    NHibernate: UPDATE Users SET Name = @p0 WHERE Id = @p1
    @p0 = 'User2'
    @p1 = '1'


    多数时候,我们先从数据库获取实例,然后再更新。但也可以直接创建实体对象,进行赋值更新。

    // 先将上面的实体改成 Id {get; set;}
    User user2 = new User(); 
    user2.Id = 1;
    user2.Name = "abcd";
    user2.Update();


    SQL

    NHibernate: UPDATE Users SET Name = @p0 WHERE Id = @p1
    @p0 = 'abcd'
    @p1 = '1'


    对比上下两次生成的 SQL 语句,会发现后一种方法更 "快" 一些。但更新的前提是必须知道所有实体属性的 "值",通常这是做不到的,所以用处不大。

    3. Save

    Save 方法比较有趣,它调用的是 NHibernate.ISession.SaveOrUpdate()。也就是说,如果是 "新" 实体,它会 Create,否则 Update。

    User user = new User();
    user.Name = "User";
    user.Save();

    Console.WriteLine(user.Id);

    User user2 = User.Find(user.Id);
    user2.Name = "User2";
    user2.Save();

    Console.WriteLine(User.Find(user.Id).Name);


    SQL

    NHibernate: INSERT INTO Users (Name) VALUES (@p0); select SCOPE_IDENTITY()
    @p0 = 'User'
    NHibernate: SELECT user0_.Id as Id0_, user0_.Name as Name0_ FROM Users user0_ WHERE user0_.Id=@p0
    @p0 = '1'
    NHibernate: UPDATE Users SET Name = @p0 WHERE Id = @p1
    @p0 = 'User2'
    @p1 = '1'
    NHibernate: SELECT user0_.Id as Id0_, user0_.Name as Name0_ FROM Users user0_ WHERE user0_.Id=@p0
    @p0 = '1'


    4. Delete

    删除实体比较简单。

    User user = new User();
    user.Name = "User";
    user.Save();

    user.Delete();


    SQL

    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '1'


    哎~~~ DeleteAll 还是老样子,要是想删除 1000 万个实体数据,我强烈建议你先去泡杯茶。

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();
    }

    User.DeleteAll();


    SQL

    NHibernate: select user0_.Id as Id, user0_.Name as Name from Users user0_
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '1'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '2'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '3'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '4'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '5'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '6'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '7'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '8'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '9'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '10'


    DeleteAll 还支持集合删除。

    List<User> users = new List<User>();

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();

      users.Add(user);
    }

    User.DeleteAll(new int[] { users[1].Id, users[3].Id });


    SQL

    NHibernate: SELECT user0_.Id as Id0_, user0_.Name as Name0_ FROM Users user0_ WHERE user0_.Id=@p0
    @p0 = '2'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '2'
    NHibernate: SELECT user0_.Id as Id0_, user0_.Name as Name0_ FROM Users user0_ WHERE user0_.Id=@p0
    @p0 = '4'
    NHibernate: DELETE FROM Users WHERE Id = @p0
    @p0 = '4'


    5. Refresh

    Refresh 的作用是从数据库刷新实体信息。

    User user = new User();
    user.Name = "User";
    user.Save();

    User user2 = User.Find(user.Id);
    user2.Name = "xxxx";
    user2.Save();

    Console.WriteLine(user.Name);
    user.Refresh();
    Console.WriteLine(user.Name);


    SQL

    NHibernate: SELECT user0_.Id as Id0_, user0_.Name as Name0_ FROM Users user0_ WHERE user0_.Id=@p0
    @p0 = '1'


    6. Find

    AR 提供了多种 Find 方法用来查找实体。

    (1) PrimaryKey

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();
    }

    User u = User.Find(3);
    Console.WriteLine(u.Name);


    我们还可以用 TryFind 代替 Find。这个方法在没找到实体时,不会触发异常。

    User u = User.TryFind(500);
    Console.WriteLine(u == null);


    (2) Property

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();
    }

    User[] us = User.FindAllByProperty("Name", "User3");
    foreach (User u in us) Console.WriteLine(u.Name);


    (3) NHibernate.Expression.ICriterion

    NHibernate Criterion 是 HQL 的 "另外一种表现方式",可用来组合多种条件。常用的有 LtExpression(<)、GeExpression(>=)、EqExpression(=)、GtExpression(>)、LeExpression(<=)、LikeExpression、AndExpression、BetweenExpression、NotExpression、NotNullExpression、NullExpression 等。还可以使用 NHibernate.Express.Order 进行排序。

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();
    }

    //User[] users = User.FindAll(new Order[]{ new Order("Id", false) }, new InExpression("Id", new object[]{ 1, 3, 5 }));
    //User[] users = User.FindAll(new EqExpression("Name", "User3"));
    //User[] users = User.FindAll(new OrExpression(new EqExpression("Name", "User1"), new EqExpression("Name", "User3")));

    //User u = User.FindFirst(new BetweenExpression("Id", 3, 6));
    User u = User.FindOne(new EqExpression("Id", 3));


    注意 FindOne 和 FindFirst 的区别,如果表达式返回的记录超过 1,FindOne 会触发异常。

    7. Exists

    Exists 可用来判断实体类型是否已经创建了对应的数据表,还可以通过主键判断实体是否存在,或者通过 hql 语句做出复杂的判断。

    // 判断数据表是否存在
    Console.WriteLine(User.Exists());

    // 通过主键判断
    Console.WriteLine(User.Exists<int>(3));

    // HQL
    Console.WriteLine(User.Exists("Name=?", "User3"));
    Console.WriteLine(User.Exists("Name=? or Id=?", "User400", 4));


    8. Query

    Query 和 Find 的最大区别是它对 HQL 的支持。AR 提供了三个 Query 对象:SimpleQuery、ScalarQuery、CountQuery。

    SimpleQuery: 主要用于获取一组信息,如实体数组、单个属性数组。

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();
    }

    //SimpleQuery query = new SimpleQuery(typeof(User), "from User user where user.Name = ?", "User2");
    //User[] users = (User[])User.ExecuteQuery(query);

    //SimpleQuery query = new SimpleQuery(typeof(User), typeof(String), "select user.Name from User user where user.Name = ?", "User2");
    //string[] names = (string[])User.ExecuteQuery(query);

    //SimpleQuery<User> query = new SimpleQuery<User>("from User user where user.Name = ?", "User2");
    //User[] users = query.Execute();

    SimpleQuery<string> query = new SimpleQuery<string>(typeof(User), "select user.Name from User user where user.Name = ?", "User2");
    string[] names = query.Execute();


    ScalarQuery: 主要用于获取单个实体对象,或单个实体的多个属性。当返回实体记录数大于 1 时会触发异常。

    for (int i = 0; i < 10; i++)
    {
      User user = new User();
      user.Name = "User" + i;
      user.Save();
    }

    //ScalarQuery query = new ScalarQuery(typeof(User), "from User user where user.Name = ?", "User2");
    //User u = (User)User.ExecuteQuery(query);

    //ScalarQuery query = new ScalarQuery(typeof(User), "select user.Id, user.Name from User user where user.Name = ?", "User2");
    //object[] properties = (object[])User.ExecuteQuery(query);

    //ScalarQuery<User> query = new ScalarQuery<User>(typeof(User), "from User user where user.Name = ?", "User2");
    //User u = query.Execute();

    ScalarQuery<object> query = new ScalarQuery<object>(typeof(User), "select user.Id, user.Name from User user where user.Name = ?", "User2");
    object properties = query.Execute();


    CountQuery: 用于统计数据库中实体记录数量。

    //CountQuery query = new CountQuery(typeof(User));
    //Console.WriteLine(User.ExecuteQuery(query));

    CountQuery query = new CountQuery(typeof(User), "Name like ?", "User1%");
    Console.WriteLine(User.ExecuteQuery(query));


    我们还可以使用重载方法中的 QueryLanguage 参数,直接执行 SQL 语句,不过要谨慎使用,因为这样一来,就有可能失去自由切换数据库的能力。

    9. Paging

    利用 CountQuery 和 ActiveRecordBase.SlicedFindAll() 我们可以实现分页查询功能。

    for (int i = 1; i <= 100; i++)
    {
      User user = new User();
      user.Name = "User" + i.ToString().PadLeft(3, '0');
      user.Save();
    }

    int pageIndex = 5;
    int pageSize = 10;

    CountQuery countQuery = new CountQuery(typeof(User), "Id < ?", 45);
    int count = (int)User.ExecuteQuery(countQuery);

    if (count > 0)
    {
      int pageCount = count / pageSize + (count % pageSize > 0 ? 1 : 0);
      pageIndex = Math.Min(pageIndex, pageCount);
      int first = Math.Max((pageIndex - 1) * pageSize, 0);

      User[] users = User.SlicedFindAll(first, pageSize, new LtExpression("Id", 45));
      foreach (User u in users) Console.WriteLine(u.Name);
    }


    SQL

    NHibernate: select COUNT(*) as x0_0_ from Users user0_ where (Id<@p0)
    @p0 = '45'
    NHibernate: SELECT top 50 this.Id as Id0_, this.Name as Name0_ FROM Users this WHERE this.Id<@p0
    @p0 = '45'


    看它生成的 SQL 语句,可见其效率不是很好。只是不知道使用 SQLite / MySQL 时,是否会使用 LIMIT 语句进行分页处理。有空研究一下……

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  • 原文地址:https://www.cnblogs.com/easyleo/p/3193868.html
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