spring data jpa查询一个实体类的部分属性
使用Spring Data Repository查询时候，通常情况下返回的是一个实体所有的属性。但是在很多情况下，我们只需要实体类的部分属性。下面的部分讲述如何实现查询一个实体类的部分属性。
首先我们定义两个实体类
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package cn.net.leadu.domain; import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToOne;/** * Created by PengChao on 2016/12/1. */@Entitypublic class Person { @Id @GeneratedValue private Long id; private String firstName; private String lastName; @OneToOne private Address address; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public Address getAddress() { return address; } public void setAddress(Address address) { this.address = address; }} |
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package cn.net.leadu.domain; import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id; /** * Created by PengChao on 2016/12/1. */@Entitypublic class Address { @Id @GeneratedValue private Long id; private String street; private String state; private String country; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getStreet() { return street; } public void setStreet(String street) { this.street = street; } public String getState() { return state; } public void setState(String state) { this.state = state; } public String getCountry() { return country; } public void setCountry(String country) { this.country = country; }} |
然后创建person实体类的repository
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package cn.net.leadu.dao; import cn.net.leadu.domain.Person;import org.springframework.data.jpa.repository.JpaRepository; /** * Created by PengChao on 2016/12/1. */public interface PersonRepository extends JpaRepository<Person, Long> { Person findByFirstName(String firstName); // 1} |
"1"方法将会返回Person对象的所有属性（包括address）
但实际情况我们不需要返回address对象，这种情况我们可以定义一个projection,如下：
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package cn.net.leadu.domain;/** * Created by PengChao on 2016/12/1. */public interface NoAddress { String getFirstName(); //2 String getLasetName(); //3} |
“2”输出person对象的firstName属性，“3”输出person对象的lastName属性
最后在Person实体类的repository中定义一个查询方法，返回值是NoAddress，如下
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package cn.net.leadu.dao;import cn.net.leadu.domain.NoAddress;import cn.net.leadu.domain.Person;import org.springframework.data.jpa.repository.JpaRepository;/** * Created by PengChao on 2016/12/1. */public interface PersonRepository extends JpaRepository<Person, Long> { NoAddress findByFirstName(String firstName);} |
返回结果只包含firstName和lastName两个属性
spring data jpa查询部分字段、多余附加字段
spring data jpa查询部分字段
第一种方法：使用 model 查询时转化
首先建立一个 model ，写上自己想要查询的字段，然后写上构造函数，这步很重要，因为spring jpa 转化时会调用这个构造方法
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public class MyModel implements Serializable { private String userName; private String name; private String gender; private String description; public MyModel() {}; public MyModel(String userName, String name, String gender, String description) { this.userName = userName; this.name = name; this.gender = gender; this.description = description; }} |
然后在 dao 类中写查询方法
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@Query(value = "select new pers.zhuch.model.MyModel(u.userName, ui.name, ui.gender, ui.description) from UserInfo ui, User u where u.id = ui.userId")public List<MyModel> getAllRecord(); |
直接在查询语句中 new model 框架底层会调用它，然后返回这个对象（这里我写了完整的类路径，不写的时候它报错说找不到类型什么的）
然后就可以获得只有指定字段的 model 了。然后就把它转成 JSON 格式就 O 了。
第二种方法：在service 里边转换成 JSON
原理其实和第一种方法差不多，只是处理结果的方式不太一样，只是这种方法我们就不在 hql 中 new Model 了，直接写查询方法
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@Query(value = "select new map(u.userName, ui.name, ui.gender, ui.description) from UserInfo ui, User u where u.id = ui.userId")public List<Map<String, Object>> getCustomField(); |
直接new map（这里得是小写，不知道大写有木有问题，反正没试，编译器提示是要小写的）
然后返回的结果是这样的
[
{
"0": "admin",
"1": "你猜",
"2": "男",
"3": "一段描述"
}, {
"0": "abc",
"1": "你猜人家",
"2": "女",
"3": "没事先挂了"
}
]
注：多表联合查询附加额外字段，亦可使用此方法。例如
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@Query("select new map(u as user,'hello' as ext) from User u where u.id=?1") List<Map<String,Object>> findExtTest(Long id); @Query(value="select u.*,'hello' as ext from user u where u.id=?1",nativeQuery = true) List<Object> findExtNativeTest(Long id); List<Map<String,Object>> rows = userRepository.findExtTest(10001l); for(Map<String,Object> row :rows) { User user = (User) row.get("user"); String ext = (String) row.get("ext"); System.out.println(user); System.out.println(ext); } List<Object> objects = userRepository.findExtNativeTest(10001l); for(Object obj :objects) { Object[] row = (Object[])obj; Long id = ((BigInteger) row[0]).longValue(); String nickName = (String)row[17]; //数据库字段顺序 String ext = (String) row[row.length-1]; System.out.println(id); System.out.println(nickName); System.out.println(ext); } |
第三种方法：select语句部分字段使用默认值
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@Query(value = "select u.user_name, ui.name, ui.gender,ui.description,'' as headImg from user_info u where u.id = 1",nativeQuery=true)public List<User> getAllRecord(); |
原文链接：https://blog.csdn.net/Peng__Chao/article/details/84885354
