[英]Performing a Hibernate Join on two tables with a One to Many Association
I basically have a database with two tables in it with the following schema: 我基本上有一个数据库,其中有两个具有以下模式的表:
Employee
|id|Age|Sex|
Table
|Table_id|Emp_id|Location|
My employee.hbm.xml file looks like: 我的employee.hbm.xml文件如下所示:
<property name="id"
type="integer"
column="emp_id" />
<property name="age"
type="integer"
column="age" />
<property name="sex"
type="string"
column="sex" />
My table.hbm.xml files looks like: 我的table.hbm.xml文件如下所示:
<property name="table_id"
type="integer"
column="table_id" />
<property name="emp_id"
type="integer"
column="emp_id" />
<property name="location"
type="string"
column="location" />
I have the necessary classes with the mappings ie the getters and setters as well. 我有必要的类与映射,即getter和setter方法。 They look like:
他们看着像是:
public class EmployeeModel {
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="id", referencedColumnName="emp_id")
private int id;
private int age;
private String sex;
//Getters and setters for all the variables
public class TableModel {
@OneToMany(mappedBy="EmployeeModel")
private int table_id;
private int emp_id;
private String location;
private int table_id;
private int emp_Id;
private String location;
//Getters and setters for all the variables
To collect the return data, I've created a newer class called EmployeeTableModel which looks like: 为了收集返回数据,我创建了一个名为EmployeeTableModel的新类,它看起来像:
public class EmployeeTableModel{
private int table_id;
private int emp_id;
private String location;
private int table_id;
private int emp_Id;
private String location;
}
As you can understand, I need to basically go a call that gives me the details of the employee and the table he is sitting in. There is a one to one correlation between them. 如您所知,我基本上需要打个电话,向我提供该员工及其所在的桌子的详细信息。它们之间存在一对一的关联。 I understand my code has a many to one correlation, please do correct me on that.
我了解我的代码具有多对一的关联,请对此进行纠正。 Presently, my query is:
目前,我的查询是:
List<EmployeeTableModel> data = sess.createCriteria(EmployeeModel.class)
.setFetchMode("TableModel", FetchMode.JOIN)
.add(Restrictions.eq("emp_id", "ANY INPUT" )).list();
I expect it to give me a query like: 我希望它能给我一个类似的查询:
select e.id,e.age,e.sex,t.table_id,t.emp_id,t.location from employee e, table t;
However, it instead gives me: 但是,它给了我:
select e.id,e.age,e.sex from employee e;
I added a variable of Employee in Table, I corrected the queries, used HQL, but I still am unable to figure out what is wrong. 我在表中添加了一个Employee变量,我更正了查询,使用了HQL,但是我仍然无法弄清楚出了什么问题。 Can someone please tell me just what is going wrong with it?
有人可以告诉我这是怎么回事吗? Or give an alternate answer?
或给出替代答案?
When using JPA/Hibernate, avoid thinking in columns when possible. 使用JPA / Hibernate时,请尽可能避免在各列中进行思考。 Think of entities and let the framework do the change.
考虑实体,让框架进行更改。
Your query is requesting just a list of EmployeeModel
, because you do 您的查询仅请求
EmployeeModel
的列表,因为您这样做
sess.createCriteria(EmployeeModel.class)
And that is what you are getting (the fact that you try to cast it to List<EmployeeTableModel>
probably causes a compile time warning and a runtime error. 这就是您得到的(尝试将其强制转换为
List<EmployeeTableModel>
的事实可能会导致编译时警告和运行时错误。
BTW, talking about thinking about entities, your model seems quite misguided. 顺便说一句,谈论实体时,您的模型似乎被误导了。 Your attributes should be entities (and not foreign keys);
您的属性应该是实体(而不是外键); instead of
代替
private int table_id;
private int emp_id;
private String location;
you do 你做
private int table_id;
private Employee employee;
private String location;
Annotations appear to be at the wrong places, too, and you do not define IDs... I advise you to read Hibernate documentation again. 注释似乎也位于错误的位置,并且您没有定义ID。我建议您再次阅读Hibernate文档。
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