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NHibernate剖析:Mapping篇之Mapping-By-Code(2):运用ModelMapper

2011-04-10 16:33 by 李永京, ... 阅读, ... 评论, 收藏, 编辑

本节内容

Mapping-By-Code概览

上一篇文章介绍了Mapping-By-Code(代码映射)的原理,这篇文章结合上篇的原理运用Mapping-By-Code(代码映射)。为了更有效的学习代码映射,这篇文章使用单元测试的方式,每一个测试用例代表某一功能实现,并且为了 直观的认识HbmMapping对象,我把HbmMapping对象序列化为字符串写入标准输出流,为此定义一个名为ShowInConsole的扩展方法。

public static class HbmMappingExtensions
{
    public static void ShowInConsole(this HbmMapping mapping)
    {
        Console.WriteLine(mapping.AsString());
    }
}

运用Mapping-By-Code

我们先定义一个非常简单的Domain模型,一个int类型的Id属性和一个string类型的Something属性,用来代码映射:

public class MyClass
{
    public int Id { get; set; }
    public string Something { get; set; }
}

1.基本映射

ModelMapper提供一种基本映射方式:使用Class方法对实体类MyClass特定映射:

  • 属性Id映射为数据库主键,对应的列名称为MyClassId、主键生成策略是HighLow策略。
  • 属性Something映射为数据库普通字段,其长度为150。

最后调用CompileMappingForAllExplicitAddedEntities方法显式所有映射的实体(这里是MyClass)编译为HbmMapping对象并输出,也可以使用CompileMappingFor方法指定实体类型。

[Test]
public void BasicMappingRegistration()
{
    var mapper = new ModelMapper();
    mapper.Class<MyClass>(cm =>
    {
        cm.Id(myclass => myclass.Id, map =>
        {
            map.Column("MyClassId");
            map.Generator(Generators.HighLow);
        });
        cm.Property(myclass => myclass.Something, map => map.Length(150));
    });

    var hbmMapping = mapper.CompileMappingForAllExplicitAddedEntities();
    //var hbmMapping = mapper.CompileMappingFor(new[] {typeof (MyClass)});
    hbmMapping.ShowInConsole();
}

NHibernate对于代码映射提供很强的灵活性,你可以像你希望的那样随意去组织映射:例如class-by-class方式、不同的映射点在不同的地方等等。

例如下面代码映射,分开去配置映射,NHibernate对重复的属性不重复映射,去合并映射:

[Test]
public void WhenDuplicatePropertiesDoesNotDuplicateMapping()
{
    var mapper = new ModelMapper();
    mapper.Class<MyClass>(cm =>
    {
        cm.Id(myclass => myclass.Id, map => map.Column("MyClassId"));
        cm.Id(myclass => myclass.Id, map => map.Generator(Generators.HighLow));
        cm.Property(myclass => myclass.Something);
        cm.Property(myclass => myclass.Something, map => map.Length(150));
    });
    var hbmMapping = mapper.CompileMappingForAllExplicitAddedEntities();
    hbmMapping.ShowInConsole();
}

你甚至也可以在两个不同地方去映射整个实体类:

[Test]
public void WhenDuplicateClassDoesNotDuplicateMapping()
{
    var mapper = new ModelMapper();
    mapper.Class<MyClass>(cm =>
    {
        cm.Id(myclass => myclass.Id, map => map.Generator(Generators.HighLow));
        cm.Property(myclass => myclass.Something);
    });

    mapper.Class<MyClass>(cm =>
    {
        cm.Id(myclass => myclass.Id, map => map.Column("MyClassId"));
        cm.Property(myclass => myclass.Something, map => map.Length(150));
    });
    var hbmMapping = mapper.CompileMappingForAllExplicitAddedEntities();
    hbmMapping.ShowInConsole();
}

2.Conformist映射

ModelMapper提供另外一种Conformist映射方式:class-by-class方式,即每个类定义一个类去映射,然后调用AddMapping方法把映射加入ModelMapper对象。

private class MyClassMap : ClassMapping<MyClass>
{
    public MyClassMap()
    {
        Id(myclass => myclass.Id, map =>
        {
            map.Column("MyClassId");
            map.Generator(Generators.HighLow);
        });
        Property(myclass => myclass.Something, map => map.Length(150));
    }
}
[Test]
public void ConformistMappingRegistration()
{
    var mapper = new ModelMapper();
    mapper.AddMapping<MyClassMap>();
    var hbmMapping = mapper.CompileMappingForAllExplicitAddedEntities();
    hbmMapping.ShowInConsole();
}

上面的映射如果查看其输出结果,都是一样:

SimpleClassMapping

3.约定

ModelMapper提供了很多事件监听器,可以通过它扩展ModelMapper。其中就是自定义约定。其实上面定义的映射从设计思想上面说也是一种约定,暂时可以称作特定约定(Specific-Convetions)

以Before开头的事件监听称作前置约定(Pre-Conventions)。从人性化角度看前置约定(Pre-Conventions)比较民主(democratic),我们映射时可以使用特定约定(Specific-Convetions)

以After开头的事件监听称作后置约定(Post-Conventions)或者称作Hard-Conventions。从人性化角度看后置约定(Post-Conventions)就比较共和(republican),不管前面怎么特定,到最后一律使用后置约定(Post-Conventions)所规定的"条约"。

例如下面例子使用前置约定(Pre-Conventions):

[Test]
public void MapClassWithConventions()
{
    var mapper = new ModelMapper();
    //option:Pre-Conventions
    mapper.BeforeMapClass +=
        (mi, t, map) => map.Id(x => x.Column((t.Name + "id").ToUpper()));
    mapper.BeforeMapProperty +=
        (mi, propertyPath, map) => map.Column(propertyPath.ToColumnName().ToUpper());

    mapper.Class<MyClass>(cm =>
    {
        cm.Id(myclass => myclass.Id, map => map.Generator(Generators.HighLow));
        cm.Property(myclass => myclass.Something);
    });
    var hbmMapping = mapper.CompileMappingForAllExplicitAddedEntities();
    hbmMapping.ShowInConsole();
}

使用后置约定(Post-Conventions):

[Test]
public void MapClassWithHardConventions()
{
    var mapper = new ModelMapper();
    //option:Hard-Conventions
    mapper.AfterMapClass +=
        (mi, t, map) => map.Id(x => x.Column((t.Name + "id").ToUpper()));
    mapper.AfterMapProperty +=
        (mi, propertyPath, map) => map.Column(propertyPath.ToColumnName().ToUpper());

    mapper.Class<MyClass>(cm =>
    {
        cm.Id(myclass => myclass.Id, map =>
                             {
                                 map.Column("MyClassId");
                                 map.Generator(Generators.HighLow);
                             });
        cm.Property(myclass => myclass.Something, map => map.Column("Whatever"));
    });
    var hbmMapping = mapper.CompileMappingForAllExplicitAddedEntities();
    hbmMapping.ShowInConsole();
}

这个例子最终主键的映射的列名称为MYCLASSID,Something映射的列名称为SOMETHING。但是其思想有些不同。

结语

NHibernate3.2新增的Mapping-By-Code(代码映射),这篇文章结合上篇的原理从整体大运用Mapping-By-Code(代码映射)功能,有个整体方向。

参考资料

Fabio Maulo:NHibernate 3.2 mapping by code

Fabio Maulo:NHibernate 3.2: (part 2) mapping by code