fastdb中的relation

最新推荐文章于 2013-02-28 10:39:14 发布

Alex_XXH

最新推荐文章于 2013-02-28 10:39:14 发布

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分类专栏：内存数据库文章标签： descriptor class 数据库

本文链接：https://blog.youkuaiyun.com/xuxinhui110/article/details/6154832

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本文介绍了在fastdb内存数据库中如何使用descriptor和class来定义类与类之间的关系，如一对一、一对多和多对多。通过dbArray和dbReference来表示Detail、Supplier和Contract类之间的关系，详细阐述了Detail与Contract以及Supplier与Contract的一对多关系。

RELARION-关系，在fastdb内存数据库中表示在类（表）之间指定是一对一，一对多，还是多对多关系。

例如：class Detail {
public:
    char const* name;
    char const* material;
    char const* color;
    real4       weight;

    dbArray< dbReference<Contract> > contracts;

    TYPE_DESCRIPTOR((KEY(name, INDEXED|HASHED),
                     KEY(material, HASHED),
                     KEY(color, HASHED),
                     KEY(weight, INDEXED),
                     RELATION(contracts, detail)));
};

class Supplier {
public:
    char const* company;
    char const* location;
    bool        foreign;

    dbArray< dbReference<Contract> > contracts;

    TYPE_DESCRIPTOR((KEY(company, INDEXED|HASHED),
                     KEY(location, HASHED),
                     FIELD(foreign),
                     RELATION(contracts, supplier)));
};

class Contract {
public:
    dbDateTime            delivery;
    int4                  quantity;
    db_int8               price;
    dbReference<Detail>   detail;
    dbReference<Supplier> supplier;

    TYPE_DESCRIPTOR((KEY(delivery, HASHED|INDEXED),
                     KEY(quantity, INDEXED),
                     KEY(price, INDEXED),
                     RELATION(detail, contracts),
                     RELATION(supplier, contracts)));
};