在项目开发过程中,查询占了很大的一个比重,一个框架的好坏也很多程度上取决于查询的灵活性和效率。
在IBatis.Net中提供了方便的数据库查询方式。
在Dao代码部分主要有两种方式:
1、查询结果为一个对象:
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2、查询结果为一个列表:
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这两种方法同时都提供了面向泛型的重载方法。这两个方法的第一个参数对应配置文件中的select id,第二个参数表示传入查询的条件
配置文件的写法:
在IBatis.Net中提供了多种查询配置的写法,我这里列出几种比较常用的方式:
1、获得一张表的所有数据
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这是最简单的方式,其中resultMap是返回查询结果的形式,需要另外配置:
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表示:得到的结果的每一条记录都映射成一个Hashtable,这个Hashtable中包含四个Key(Id,FirstName......)
2、根据条件查询(简单方式):
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只有一个条件,传入参数的类型是int型,拼写sql时直接用 #value#就可以了
3、根据条件查询(较复杂方式):
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传入参数是一个Hashtable,MaximumAllowed等表示的是Hashtable里的key值,用$$包含起来。
并且查询时可以根据条件是否为空动态拼写sql语句
PS:输入参数同样可以使用Account类,注意对应的键要和类中的属性名一致(大小写也要一样)
4、多表查询
多表查询时返回参数有三种方式,一种是新建一个类,在这个类中包含这多个表的所有属性,还有一种就是直接返回Hastable就可以了:
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PS:这里的HashMap实际上就是Hashtable
第三种方式是使用IBatis中的复杂属性(感谢Anders Cui 的提醒)
比如现在有两张表Account和Degree,使用Account_ID关联,那么需要在原有的基础上修改:
1、修改Account实体类,加入一个属性:
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这样是一个1:1的关系,也可以加入IList DegreeList的属性,这样查询的结果就是一个1:n的关系
2、修改配置文件:
在resultMaps节加入:
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对于Degree属性,还可以加入lazyLoad=true 延迟加载,优化性能(也就是开始时并没有实际查询数据库,当用到属性Degree时,才实际的查询相应的数据)
在statements节加入:
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这样可以正确的查询出结果,符合OO,但是也有两个小问题:
1、比较麻烦,不够灵活
2、性能受影响:
这种方式其实和Hibernet比较类似了,查询时首先执行
select * from Accounts order by Account_ID
然后根据这条语句的结果,比如有100条记录,那就要执行100次以下的语句:
select * from Degree where Account_id = @param0
关于输入输出:
从上面可以看到输入时可以使用:parameterClass和parameterMap,输出时可以使用:resultClass和resultMap
对于resultMap和parameterMap我们需要另外进行配置(如上所示)
对于parameterClass和resultClass,如果是C#固有类型可以直接使用,如果是我们自定义类可以在SqlMap.config中先统一声明一下:
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