java - 在单独的文件中定义 JPA 实体图

Question

是否可以在与实体定义不同的单独文件中为 JPA 实体(@NamedEntityGraph 注释)定义实体图？

如果我的项目变得有点复杂，我在这些定义的实体之前就会有一大堆丑陋/不可读的代码。

Answer 1

假设您有一个使用 @NamedEntityGraph 注释的实体，如下所示:

@Entity
@NamedEntityGraph(name = "Project.graph"
  attributeNodes = {
    @NamedAttributeNode(value = "deadline"),
    @NamedAttributeNode(value = "employees", subgraph = "Employee.subgraph")},
    ...
  subgraphs = {
    @NamedSubgraph(name = "Employee.subgraph",
      attributeNodes = {
        @NamedAttributeNode(value = "salary")}
        ...
  )}
)
public class Project {
    ...
    @Temporal(TemporalType.DATE)
    private Date deadline;

    @OneToMany(mappedBy="project", cascade = CascadeType.PERSIST)
    private Collection<Employee> employees;
    ...
}

在 persistence.xml 中添加对 XML 映射文件的引用(假设为 orm.xml):

...
<mapping-file>META-INF\orm.xml</mapping-file>
...

对于上面的 @NamedEntityGraph 可以定义如下:

<?xml version="1.0" encoding="UTF-8"?>
<entity-mappings xmlns="http://xmlns.jcp.org/xml/ns/persistence/orm" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence/orm http://xmlns.jcp.org/xml/ns/persistence/orm_2_1.xsd"
    version="2.1">
    ...
    <entity class="com.example.Project">
        <named-entity-graph>
            <named-attribute-node name="deadline" />
            <named-attribute-node name="projects" subgraph="Employee.subgraph" />
            ...
            <subgraph name="Employee.subgraph">
                <named-attribute-node name="salary" />
                ...
            </subgraph>
        </named-entity-graph>
    </entity>
</entity-mappings>