具有多个元素的 Hibernate 包

Question

我有一个包，其结构如下所示：

<bag name="foo" fetch="select" table="table_of_foos">
    <key column="foo_ids"/>
    <many-to-many class="Bar" column="bar_ids"/>
</bag>

我的“table_of_foos”表有两列：“foo_ids”和“bar_ids”，这两列都不唯一。我想向该表添加另一列，该列包含有关 foos 与 Bars 关系的一些信息，以便我的表可以包含三列。然后，我希望能够在我的网络应用程序中访问此信息。

不幸的是，我似乎无法向包中添加属性或元素。我想做的是这样的：

<bag name="foo" fetch="select" table="table_of_foos">
    <key column="foo_ids"/>
    <many-to-many class="Bar" column="bar_ids"/>
    <element column="still_valid" type="integer"/>
</bag>

完成此任务的最佳方法是什么？

Answer 1

如果您的连接表需要除（复合）主键之外的附加列，您必须实现附加连接类。

public class Foo {

    Collection<FooBar> bar = new ArrayList<FooBar>();

}

public class Bar {

    Collection<FooBar> foo = new ArrayList<FooBar>();

}

连接类（需要复合主键 - 作为静态内部类实现）描述如下

public class FooBar {

    private FooBarId fooBarId;

    private String additionalProperty;

    public static class FooBarId implements Serializable {

        private Integer fooId;
        private Integer barId;

        private Foo foo;
        private Bar bar;

        // getter's and setter's

        public FooBarId() {}
        public FooBarId(Integer fooId, Integer barId) {
            this.fooId = fooId;
            this.barId = barId;
        }

        public boolean equals(Object o) {
            if(!(o instanceof FooBarId))
                return false;

            FooBarId other = (FooBarId) o;
            return new EqualsBuilder()
                       .append(getFooId(), other.getFooId())
                       .append(getBarId(), other.getBarId())
                       .isEquals();
        }

        public int hashCode() {
            return new HashCodeBuilder()
                       .append(getFooId())
                       .append(getBarId())
                       .hashCode();
        }

    }

}

将您的映射重写为

/* Foo.class */ 

<bag name="bar" table="table_of_foos">
    <key column="BAR_ID" insert="false" update="false"/>
    <one-to-many class="FooBar" table="table_of_foos"/>
</bag>

/* Bar.class */ 

<bag name="foo" table="table_of_foos">
    <key column="FOO_ID" insert="false" update="false"/>
    <one-to-many class="FooBar" table="table_of_foos"/>
</bag>

And FooBar 映射

<class name="FooBar">
    <composite-id name="fooBarId" class="FooBar$FooBarId">
        <key-property name="fooId" column="FOO_ID"/>
        <key-property name="barId" column="BAR_ID"/>
    </composite-id>
    <property name="additionalProperty" type="string"/>
    <many-to-one name="foo" column="FOO_ID" class="Foo" insert="false" update="false"/>
    <many-to-one name="bar" column="BAR_ID" class="Bar" insert="false" update="false"/>
</class>

如果需要，您还可以映射复合元素而不是连接类（A 组件元素不需要（复合）主键，并且将其生命周期绑定到其所属实体实例的生命周期）

创建复合元素（现在没有标识符）

public class FooBar {

    private String additionalProperty;

    private Foo foo;
    private Bar bar;

}

并定义以下内容 。映射

/* Foo.class */ 

<bag name="bar" table="table_of_foos">
    <key column="BAR_ID"/>
    <composite-element class="FooBar">
        <property name="additionalProperty" type="string"/>
        <many-to-one name="foo" column="FOO_ID" class="Foo" insert="false" update="false"/>
        <many-to-one name="bar" column="BAR_ID" class="Bar"/>
    </composite-element>
</bag>

/* Bar.class */ 

<bag name="foo" table="table_of_foos">
    <key column="FOO_ID"/>
    <composite-element class="FooBar">
        <property name="additionalProperty" type="string"/>
        <many-to-one name="foo" column="FOO_ID" class="Foo" insert="false" update="false"/>
        <many-to-one name="bar" column="BAR_ID" class="Bar"/>
    </composite-element>
</bag>

Answer 2

我无法按照 Arthur Ronald FD Garcia 编写的方式使这些映射正常工作。
此代码不起作用并导致 MappingException。

无效的尝试

<set name="StoreDepartments" table="`ou_store_org_unit`">
    <key column="`ou_id`" />
    <composite-element class="NHibernate.Map.OrganizationUnit+StoreDepartment+Relation, CentralDataLayer">
        <property name="Id" column="`ou_store_id`" type="Int32" />
        <many-to-one name="OrganizationUnit" column="`ou_id`" class="NHibernate.Map.OrganizationUnit, CentralDataLayer" />
        <many-to-one name="StoreDepartment" column="`store_ou_id`" class="NHibernate.Map.OrganizationUnit+StoreDepartment, CentralDataLayer" />
    </composite-element>
</set>

Resulting Error: Repeated column in mapping for collection:
NHibernate.Map.OrganizationUnit.StoreDepartments column: ou_id

我能够通过以下方式让它工作。

有效尝试

<set name="StoreDepartments" table="`ou_store_org_unit`">
    <key column="`ou_id`" />
    <composite-element class="NHibernate.Map.OrganizationUnit+StoreDepartment+Relation">
        <parent name="OrganizationUnit" />
        <property name="Id" column="`ou_store_id`" type="Int32" />
        <many-to-one name="StoreDepartment" column="`store_ou_id`" class="NHibernate.Map.OrganizationUnit+StoreDepartment" />
    </composite-element>
</set>

另外：

如果 nHibernate 尝试更新您的集（即使您没有修改它），请尝试覆盖 GetHasCode 和 Equals 方法。更多信息。