使用投影从 child table 中获取特定列

Question

我有两张桌子

Loan (id, amount, duration)

LoanStatus(id, status, loan_id)   // just an example, but it has lot more fields in this table

Loan.java

public class Loan{

    private int id;
    private int amount;
    private int duration;
    private LoanStatus loanStatus;

    // getter and setters

}

LoanStatus.java

public class LoanStatus{   // just an example, but it has many fields than what actually given

    private int id;
    private String status;
    private Loan loan;

    //getter and setters

}

现在我只想使用投影获得 amount 、 duration 、 loanStatus.status 。我已使用 createAlias() 成功获取该特定列，但将其设置为 setter.

时会出现问题

Criteria criteria = getSession().createCriteria(Loan.class,"loan");
    criteria.createAlias("loan.loanStatus", "loanStatus")
            .setProjection(Projections.projectionList().add(Projections.property("id"),"id")
            .add(Projections.property("amount"),"amount")
            .add(Projections.property("duration"),"duration")
            .add(Projections.property("loanStatus.status"), "loanStatus"))
            .add(Restrictions.eq("id", id))
            .setResultTransformer(Transformers.aliasToBean(Loan.class));
    return criteria.list();

我有一个错误如下。

IllegalArgumentException occurred while calling setter for property [com.site.dto.Loan.loanStatus (expected type = com.site.dto.LoanStatus)]; target = [com.site.dto.Loan@4083974a], property value = [Pending]

所以我得到了预期的列值 "Pending"，但问题是将其设置为 setter。我见过很多关于投影的问题，但其中大部分是基于使用投影的限制，而不是使用投影获取 child 的特定列。

Answer 1

编写您自己的自定义转换器。以下实现可能正是您所需要的

https://github.com/samiandoni/AliasToBeanNestedResultTransformer。他们的文档中写的用法示例

class Person {
  private Long id;
  private String name;
  private Car car;
  // getters and setters
}

class Car {
  private Long id;
  private String color;
  // getters and setters
}

List<Person> getPeople() {
  ProjectionList projections = Projections.projectionList()
    .add(Projections.id().as("id"))
    .add(Projections.property("name").as("name"))
    .add(Projections.property("c.id").as("car.id"))
    .add(Projections.property("c.color").as("car.color"));

  Criteria criteria = getCurrentSession().createCriteria(Person.class)
    .createAlias("car", "c")
    .setProjection(projections)
    .setResultTransformer(new AliasToBeanNestedResultTransformer(Person.class));

  return (List<Person>) criteria.list();
}

// each car of Person will be populated

使用投影从 child table 中获取特定列

Using Projecions to fetch a particular column from child table

java

mysql

hibernate

projection