使用Projecions从子表中获取特定的列 [英] Using Projecions to fetch a particular column from child table

问题描述

我有两张表
$ b $ pre $ code贷款（id，金额，持续时间）

LoanStatus（id ，status，loan_id）//只是一个例子，但它在这个表中有很多字段

贷款.java

  public class Loan {
 
 private int id; 
 private int amount; 
 private int duration; 
私人LoanStatus loanStatus; 
 
 // getter and setters 
 
} 
  

LoanStatus.java

  public class LoanStatus {//只是一个例子，但它有很多字段，而不是实际给出的
 
 private int id; 
私人字符串状态; 
私人贷款贷款; 
 
 // getter and setters 
 
} 
  

现在我只想得到金额，持续时间， loanStatus.status 使用投影。我已经使用 createAlias（）来成功获取特定列，但是将其设置为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。状态），loanStatus））
 .add（Restrictions.eq（id，id））
 .setResultTransformer（Transformers.aliasToBean（Loan.class））; 
 return criteria.list（）; 
  

我有一个错误，如下所示。

 在为set [com.site.dto.Loan.loanStatus（expected type = com.site.dto.LoanStatus）]调用setter时发生IllegalArgumentException; target = [com.site.dto.Loan@4083974a]，property value = [Pending] 
  

我收到了预期的列值Pending，但问题在于将其设置为setter时。我看到很多预测问题，但其中大多数是基于使用投影的限制，但不是使用投影来获取孩子的特定列。

>

编写您自己的定制变压器。以下实现可能正是您需要的功能

https：/ /github.com/samiandoni/AliasToBeanNestedResultTransformer 。使用示例写在他们的文档中

  class Person {
 private Long id; 
私人字符串名称; 
私家车车; 
 // getters and setters 
} 
 
 class Car {
 private Long id; 
私有字符串颜色; 
 //获得者和设置者
} 
 
列表< Person> getPeople（）{
 ProjectionList预测= 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。色 ），为（ car.color））; 
 
 Criteria criteria = getCurrentSession（）。createCriteria（Person.class）
 .createAlias（car，c）
 .setProjection（预测）
。 setResultTransformer（新的AliasToBeanNestedResultTransformer（Person.class））; 
 
 return（List< Person>）criteria.list（）; 
} 
 
 //每个人的车将被填充
  

I have two tables

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

}

Now I would like to get only amount , duration , loanStatus.status using Projections. I've used createAlias() to successfully fetch that particular column, but the problem occurs when setting it to a setter.

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();

I've an error which as follows.

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]

So I'm getting my expected column value "Pending", but the problem is when setting it to a setter. I've seen many question for projections, but most of them was based on Restrictions using Projections but not fetching a child's particular column using projections.

解决方案

Write your own custom transformer. The following implementation might be exactly what you need

https://github.com/samiandoni/AliasToBeanNestedResultTransformer . The usage example as written in their docs

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

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