NBear-支持基于操作符重载的强类型Where及OrderBy查询-技术开发专区

NBear-支持基于操作符重载的强类型Where及OrderBy查询

作者：teddyma 编辑：振宇 2007-06-05 16:30

【IT168 技术文档】

从v2.2.1版起，NBear开始支持强类型的实体查询语法。例如，我们可以以如下的语法查询需要的数据：

LocalUser[] users = gateway.Select<LocalUser>(_Entity.LocalUser.Id > 5 | _Entity.LocalUser.LoginId == "teddy", _Entity.LocalUser.Id.Desc & _Entity.LocalUser.LoginId.Asc);

注意，Select函数的两个参数分别为两个强类型表达式，一个是一组查询条件，另一个是排序条件。

以上代码等价于：

LocalUser[] users = gateway.Select<LocalUser>("[Id] > @Id or [LoginId] = @LoginId", "[Id] desc, [LoginId]", new object[] { 5, "teddy" });

    我们可以看到，采用第一种语法的好处有：

    · 强类型，对于代码错误拥有编译器错误检查；
    · 更直观；
    · 独立与数据库特定的SQL语法，从而隔离了业务层和特定数据库的耦合；

    使用Entity Configurator生成强类型实体查询代码

    要让程序能够访问到_Entity命名空间下的这些强类型查询对象，需要先使用Entity Configurator生成强类型实体查询代码。只需在Entity Configurator中载入实体程序集，设置要对应的元数据，点击工具的Code->Generate EntityQuery Code菜单项，再将生成的代码复制到需要的任意程序集中，生成的代码及包含了所有实体的强类型查询对象。

    可用操作符

    NBear的像类型实体查询语法支持的操作符有：&(与)，|(或)，==(等于)，!=(不等于)，>(大于)，<(小与)，>=(大于等于)，<=(小于等于)，!(否)，以及.Like()注意，Like是一个函数，可以以_Entity.User.LoginId.Like("teddy")这样的方式使用。

    对于OrderBy部分，唯一的可用操作符是&，即表示组合多个排序条件。

    代码示例

    下面的代码是使用Entity Configurator工具为使用Entity Configurator设置实体元数据、生成数据库创建脚本一文中所示的实体生成的强类型实体查询代码：

namespace _Entity
{
public class AgentUser
{
public static PropertyItem LoginId = new PropertyItem("LoginId", "[", "]", "@");
public static PropertyItem Id = new PropertyItem("Id", "[", "]", "@");
public static PropertyItem Name = new PropertyItem("Name", "[", "]", "@");
public static PropertyItem PrivilegeOwnerId = new PropertyItem("PrivilegeOwnerId", "[", "]", "@");
}
public class GhostUser
{
public static PropertyItem Id = new PropertyItem("Id", "[", "]", "@");
public static PropertyItem Name = new PropertyItem("Name", "[", "]", "@");
public static PropertyItem PrivilegeOwnerId = new PropertyItem("PrivilegeOwnerId", "[", "]", "@");
}
public class IdentableEntity
{
public static PropertyItem Id = new PropertyItem("Id", "[", "]", "@");
public static PropertyItem Name = new PropertyItem("Name", "[", "]", "@");
}
public class IdFactory
{
public static PropertyItem NextId = new PropertyItem("NextId", "[", "]", "@");
}
public class LocalUser
{
public static PropertyItem Password = new PropertyItem("Password", "[", "]", "@");
public static PropertyItem LoginId = new PropertyItem("LoginId", "[", "]", "@");
public static PropertyItem Id = new PropertyItem("Id", "[", "]", "@");
public static PropertyItem Name = new PropertyItem("Name", "[", "]", "@");
public static PropertyItem PrivilegeOwnerId = new PropertyItem("PrivilegeOwnerId", "[", "]", "@");
}
public class Loginable
{
public static PropertyItem LoginId = new PropertyItem("LoginId", "[", "]", "@");
}
public class PasswordLoginable
{
public static PropertyItem Password = new PropertyItem("Password", "[", "]", "@");
public static PropertyItem LoginId = new PropertyItem("LoginId", "[", "]", "@");
}
public class PrivilegeAssignable
{
public static PropertyItem PrivilegeOwnerId = new PropertyItem("PrivilegeOwnerId", "[", "]", "@");
}
public class User
{
public static PropertyItem Id = new PropertyItem("Id", "[", "]", "@");
public static PropertyItem Name = new PropertyItem("Name", "[", "]", "@");
public static PropertyItem PrivilegeOwnerId = new PropertyItem("PrivilegeOwnerId", "[", "]", "@");
}
public class UserGroup
{
public static PropertyItem Comment = new PropertyItem("Comment", "[", "]", "@");
public static PropertyItem Id = new PropertyItem("Id", "[", "]", "@");
public static PropertyItem Name = new PropertyItem("Name", "[", "]", "@");
public static PropertyItem PrivilegeOwnerId = new PropertyItem("PrivilegeOwnerId", "[", "]", "@");
}
}

关注我们