Question

我正在尝试构建一个select语句，这将允许我在应用程序启动时构建一个本地应用程序缓存。我的表结构如下所示;

enter image description here

我知道要得到一些帮助，我必须证明我已经尝试过但非常

我正在使用hibernate，它应该让事情变得更容易但是我真的遇到了障碍，我能想到的唯一方法是选择所有字段，然后在表id匹配上做左外连接，但问题是使用这种方法的是，一个用户可以拥有0-1个名片/ 0-1个社交卡，0-1个人卡，这意味着当我离开外部联接时，某些用户可能会丢失一些数据。 personalInfo / Logindetails和Device Data都是1：1映射

有没有更有效的方法在hibernate中进行select，这样我可以轻松构建缓存？

理想情况下，我想构建一个这样的对象;

public class User {

    private BusinessCard businessCard;
    private SocialCard socialCard;
    private PersonalCard personalCard;

    private PersonalInformation personalInformation;
    private LoginDetails loginDetails;
    private DeviceData deviceData;


    public BusinessCard getBusinessCard() {
        return businessCard;
    }

    public void setBusinessCard(BusinessCard businessCard) {
        this.businessCard = businessCard;
    }

    public SocialCard getSocialCard() {
        return socialCard;
    }

    public void setSocialCard(SocialCard socialCard) {
        this.socialCard = socialCard;
    }

    public PersonalCard getPersonalCard() {
        return personalCard;
    }

    public void setPersonalCard(PersonalCard personalCard) {
        this.personalCard = personalCard;
    }

    public PersonalInformation getPersonalInformation() {
        return personalInformation;
    }

    public void setPersonalInformation(PersonalInformation personalInformation) {
        this.personalInformation = personalInformation;
    }

    public LoginDetails getLoginDetails() {
        return loginDetails;
    }

    public void setLoginDetails(LoginDetails loginDetails) {
        this.loginDetails = loginDetails;
    }

    public DeviceData getDeviceData() {
        return deviceData;
    }

    public void setDeviceData(DeviceData deviceData) {
        this.deviceData = deviceData;
    }

}

由于

Answer 1

来自Hibernate Community Documentation - Charpter 7 - Association Mappings：

<强> 7.2.1。许多对一

单向多对一关联是最常见的单向关联。

<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>

create table Person ( 
    personId bigint not null primary key
    , addressId bigint not null 
)

create table Address ( 
    addressId bigint not null primary key 
)

<强> 7.2.2。一对一的

外键上的单向一对一关联几乎相同。唯一的区别是列唯一约束。

<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId" 
        unique="true"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>

create table Person ( 
    personId bigint not null primary key
    , addressId bigint not null unique 
)

create table Address ( 
    addressId bigint not null primary key 
)

这是你如何映射一对一的关系。请注意，除了many-to-one。

之外，这与sa unique constraint映射相同

现在已经映射了您的班级，您的Person班级将如下所示。

public class Person {
    public Address getAddress() { return address; }
    public void setAddress(Address address) { this.address = address; }

    public int getId() { return id; }
    protected void setId(int id) { this.id = id; }

    private Address address;
    private int id;
}

回答您的问题

这完全取决于您希望如何保留数据。如上所述，我会将BusinessCard，SocialCard和PersonalCard的身份放入User表中，以便每个用户可以存在一张且只有一张卡。

<class name "User" table="Users">
    <id name="id" column="userId">
        <generator class="native" />
    </id>
    <many-to-one name="businessCard"
        column="businessCardId"
        unique="true"
        not-null="true" />
    <many-to-one name="socialCard"
        column="socialCardId"
        unique="true"
        not-null="true" />
    <many-to-one name="personalCard"
        column="personalCardId"
        unqiue="true"
        not-null="true" />
</class>

<class name="BusinessCard" table="BusinessCards">
    <id name="id" column="businessCardId">
        <generator class="native" />
    </id>
</class>

<class name="SocialCard" table="SocialCards">
    <id name="id" column="socialCardId">
        <generator class="native" />
    </id>
</class>

<class name="PersonalCard" table="PersonalCards">
    <id name="id" column="personalCardId">
        <generator class="native" />
    </id>
</class>

如何构造SQL语句以避免这么多连接

1 个答案: