OpenJPA 1.2.x使用JPQL选择树结构 [英] OpenJPA 1.2.x select tree structure using JPQL
问题描述
我正在使用OpenJPA 1.2.x(JPA1).问题是我无法使用JPQL来查询树结构.
I'm using OpenJPA 1.2.x (JPA1). The problem is that I can't get on with querying tree structure using JPQL.
请参见我的实体
@NamedQueries(
{
@NamedQuery(
name="Department.getFullTree",
query="SELECT dep FROM Department dep LEFT JOIN fetch dep.children"
)
}
)
@Entity
public class Department {
public static final Long ROOT_ID = 0L;
@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="DEPARTMENT_SEQ")
@SequenceGenerator(name="DEPARTMENT_SEQ", sequenceName="DEPARTMENT_SEQ", allocationSize=1)
@Column(name="ID")
private Long id;
@Column(name="PARENT_ID")
private Long parentId;
@ManyToOne(targetEntity = Department.class, fetch = FetchType.EAGER)
@JoinColumn(name = "PARENT_ID")
private Department parent;
@Column(name="LABEL")
private String label;
@OneToMany(mappedBy = "parent",
targetEntity = Department.class,
fetch=FetchType.LAZY,
cascade = {CascadeType.PERSIST, CascadeType.ALL})
private List<Department> children;
还有我的无状态bean方法:
And my stateless bean method:
public Department getFullTree(){
em.createNamedQuery("Department.getFullTree").getResultList();
Department root = em.find(Department.class, Department.ROOT_ID);
return root;
}
我的目标是从根开始获得完整的部门树. 我已经尝试过这种方法:
My aim is to get full department tree starting from root. I've tried this approach:
是真的吗?我正在使用DB2.并将在将来使用. 用于获取整棵树的JPA查询
Is that true? I'm using DB2. And will use it in future. JPA query for getting the whole tree
这似乎不起作用: http://www.tikalk.com/java/用jpa和休眠加载树
我尝试重复,但是遍历树时出现stackoverflow错误(根本不超过200个节点). 调试输出显示root本身具有孩子身份,因此它是圆形链接结构...
I've tried to repeat, but I get stackoverflow error while traversing tree (don't have more than 200 nodes at all). Debug output showed that root has itself as a child, so it's round-linked structure...
接下来我要尝试什么?
UPD: 这是我的遍历代码:
UPD: Here is my traverse code:
public class TreeTagHelper {
private static final Logger LOG = LoggerFactory.getLogger(TreeTagHelper.class);
private Department root;
private JspWriter out;
public TreeTagHelper(Department root, JspWriter out){
LOG.trace("#init");
this.root = root;
this.out = out;
}
public void printTree() throws Exception{
LOG.trace("#printTree -> start");
out.println("<ul id=\"tree-root\"> ");
for(Department dep : root.getChildren()){
printNode(dep, out);
}
closeUL(out);
LOG.trace("#printTree -> end");
}
public static void printNode(Department dep, JspWriter out) throws Exception{
LOG.trace("#printNode title[{}] children.size()[{}]",dep.getLabel(), (dep.getChildren() == null ? "NULL" : dep.getChildren().size()) );
openLI(out);
out.print("<span id=\"tree_node_"+dep.getId()+"\" class=\"ekp-tree-node\" onclick=\"ekpCommon.tree.toggleBullet(this)\">"+dep.getLabel()+"</span>");
if(dep.getChildren()!=null){
openUL(out);
for(Department child : dep.getChildren()){
printNode(child, out);
}
closeUL(out);
}
closeLI(out);
}
public static void openUL(JspWriter out) throws Exception{
out.println("<ul>");
}
public static void closeUL(JspWriter out) throws Exception{
out.println("</ul>");
}
public static void openLI(JspWriter out) throws Exception{
out.println("<li>");
}
public static void closeLI(JspWriter out) throws Exception{
out.println("</li>");
}
LOG.trace(#printNode title [{}] children.size()[{}]",dep.getLabel(),(dep.getChildren()== null?"NULL":dep.getChildren( ).size()));
LOG.trace("#printNode title[{}] children.size()[{}]",dep.getLabel(), (dep.getChildren() == null ? "NULL" : dep.getChildren().size()) );
始终输出:#printNode标题[所有部门] children.size()[19]" 似乎根(所有部门")有19个孩子.是的,我在数据库中检查了它. 但是每个孩子都是根! 所以它是无限的结构... ???根不生孩子?它会自我获取吗?
always outputs: "#printNode title[All departments] children.size()[19]" Seems like the root("All departments") has 19 children. It's true, I checked it in my DB. But each children is the root! So it's infinite structure...??? Root doesn't get children? It fetches itself?
推荐答案
我尝试重复,但是遍历树时出现stackoverflow错误(根本不超过200个节点).调试输出显示root本身具有孩子身份,因此它是圆形链接结构...
I've tried to repeat, but I get stackoverflow error while traversing tree (don't have more than 200 nodes at all). Debug output showed that root has itself as a child, so it's round-linked structure...
那么您的数据很可能是错误的.仔细检查根是否没有父级.
Then your data are very likely wrong. Double check that the root has no parent.
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