Question

我目前正在项目中使用Witty和DBO以及SQLite3，现在我需要加入一个相关的表来获取行数。

表格

CREATE TABLE "rfnode" (
  "mac" varchar(16) not null,
  "zone" integer not null,
  "subZone" integer not null,
  "unit" text not null,
  "pwm" integer not null,
  "led" integer not null,
  "network" integer not null,
  "lastContact" text,
  "ioConfiguration" integer not null,
  primary key ("mac")
)

CREATE TABLE "nodemeasure" (
  "id" integer primary key autoincrement,
  "mac" text not null,
  "type" integer not null,
  "date" text,
  "batchDate" text,
  "value" real not null
)

通常，SQL查询是：

SELECT
    rn.*,
    COUNT(nm.id) AS measuresCount
FROM rfnode rn
LEFT JOIN nodemeasure nm
    ON nm.mac = rn.mac
GROUP BY rn.mac

现在问题是我无法弄清楚如何通过使用Wt / DBO库来查询和获取结果。

首次尝试

class RFNode
{
    public:
        std::string mac, unit;
        int zone = 0, subZone = 0, pwm = 0, led = 0, network = 0, ioConfiguration = 0, measuresCount = 0;
        Wt::WDateTime lastContact;

        RFNode()
        {
            mac             = "";
            zone            = 0;
            subZone         = 0;
            unit            = "";
            pwm             = 8;
            led             = 8;
            network         = 0;
            ioConfiguration = 0;
            measuresCount   = 0;
        }

        RFNode(std::string p_sMAC, int p_nZone, int p_nSubZone, std::string p_sUnit, int p_nPWM, int p_nLED, int p_nNetwork, Wt::WDateTime p_oLastContact, int p_nIOConfiguration, int p_nMeasuresCount = 0)
        {
            mac             = p_sMAC;
            zone            = p_nZone;
            subZone         = p_nSubZone;
            unit            = p_sUnit;
            pwm             = p_nPWM;
            led             = p_nLED;
            network         = p_nNetwork;
            lastContact     = p_oLastContact;
            ioConfiguration = p_nIOConfiguration;
            measuresCount   = p_nMeasuresCount;
        }

        template<class Action>
        void persist(Action& a)
        {
            dbo::id(a,      mac,            "mac",16);
            dbo::field(a,   zone,           "zone");
            dbo::field(a,   subZone,        "subZone");
            dbo::field(a,   unit,           "unit");
            dbo::field(a,   pwm,            "pwm");
            dbo::field(a,   led,            "led");
            dbo::field(a,   network,        "network");
            dbo::field(a,   lastContact,    "lastContact");
            dbo::field(a,   ioConfiguration,"ioConfiguration");
            dbo::field(a,   measuresCount,  "measuresCount");
        };
};

查询：

Wt::Dbo::collection<Wt::Dbo::ptr<RFNode>> lTemp = m_oSession.query<Wt::Dbo::ptr<RFNode>>("SELECT rn.*, COUNT(nm.id) AS measuresCount FROM rfnode rn LEFT JOIN nodemeasure nm ON nm.mac = rn.mac").resultList();

指向Session::query(): too many aliases for result。

第二次尝试

使用相同类别的RFNode，但删除了字段measuresCount。

typedef Wt::Dbo::ptr_tuple<RFNode, int>::type RFNodeJoin;
        typedef Wt::Dbo::collection<RFNodeJoin> RFNodeJoinC;

        RFNodeJoinC lTemp = m_oSession.query<RFNodeJoin>("SELECT rn.*, COUNT(nm.id) AS measuresCount FROM rfnode rn LEFT JOIN nodemeasure nm ON nm.mac = rn.mac GROUP BY rn.mac").resultList();

        std::vector<RFNodeJoin> lTransition(lTemp.begin(),lTemp.end());

但它没有编译，导致错误：error: request for member ‘persist’ in ‘obj’, which is of non-class type ‘int’。我想我需要为每个表映射一个类，但由于我想要一个计数而没有现有的字段，我认为int类不会完成这项工作。

Answer 1

最后通过反复试验找到了解决方案......

首先，RFNode类不再有字段measuresCount。

请求和迭代如下：

Wt::Dbo::collection<boost::tuple<Wt::Dbo::ptr<RFNode>, int>> lTemp = m_oSession.query<boost::tuple<Wt::Dbo::ptr<RFNode>, int>>("SELECT rn, COUNT(nm.id) FROM rfnode rn LEFT JOIN nodemeasure nm ON nm.mac = rn.mac GROUP BY rn.mac").resultList();

for(Wt::Dbo::collection<boost::tuple<Wt::Dbo::ptr<RFNode>, int>>::const_iterator i = lTemp.begin();i != lTemp.end();++i)
{
    Wt::Dbo::ptr<RFNode> pRFNode;
    int nNodeMeasureCount;

    boost::tie(pRFNode,nNodeMeasureCount) = *i;

    lNodes.push_back(
            RFNode(
                    pRFNode->mac,
                    pRFNode->zone,
                    pRFNode->subZone,
                    pRFNode->unit,
                    pRFNode->pwm,
                    pRFNode->led,
                    pRFNode->network,
                    pRFNode->lastContact,
                    pRFNode->ioConfiguration,
                    nNodeMeasureCount
            )
    );
}

希望有一天能帮助别人！

ORM加入表行计数

1 个答案: