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jpa 命名查询 JPA 命名查询参数类型示例

2023-03-09 03:18 Java教程

jpa 命名查询 JPA 命名查询参数类型示例

jpa 命名查询

JPA 命名查询是 JPA 提供的一种查询方式，它可以让我们在实体类中定义一个静态的查询，这样就可以在其他地方直接使用这个查询。

JPA 命名查询有两种形式：NamedQuery 和 NamedNativeQuery。NamedQuery 是使用 JPQL 语句来定义的，而 NamedNativeQuery 是使用原生 SQL 语句来定义的。

@Entity 
@Table(name = "user") 
@NamedQueries({ 
    @NamedQuery(name = "User.findByName", query = "SELECT u FROM User u WHERE u.name = :name"), 
    @NamedQuery(name = "User.findByAge", query = "SELECT u FROM User u WHERE u.age = :age") 
}) 
public class User { 

    // 省略其他代码... 
}

上面的代码中，我们使用 @NamedQueries 注解来定义了两个命名查询，分别是根据 name 和 age 条件查询 User 的信息。

我们可以通过 EntityManager 的 createNamedQuery() 方法来获取这两个命名查询：

TypedQuery<User> query1 = entityManager.createNamedQuery("User.findByName", User.class); 
TypedQuery<User> query2 = entityManager.createNamedQuery("User.findByAge", User.class);

然后我们就可以对这些 Query 进行设置参数和执行操作了：

query1.setParameter("name", "John"); 
List<User> users1 = query1.getResultList(); 
query2.setParameter("age", 20); 
List<User> users2 = query2.getResultList();

JPA 命名查询有很多优势，例如能够将 SQL 语句和 Java 类分离开来、能够重复使用相同的 SQL 语句、能够减少字符串字面量带来的问题、能够减少代码量、能够易于理解和修改等。因此 JPA 命名查询是一种很好的方式来实现数据库访问。

JPA 命名查询参数类型示例

JPA教程 - JPA命名查询参数类型示例


在命名查询中，我们还可以添加参数。

@Entity
@NamedQueries({
  @NamedQuery(name="findEmployeesAboveSal",
              query="SELECT e " +
                    "FROM Employee e " +
                    "WHERE e.department = :dept AND " +
                    "      e.salary > :sal"),
  @NamedQuery(name="findHighestPaidByDepartment",
              query="SELECT e " +
                    "FROM Employee e " +
                    "WHERE e.department = :dept AND " +
                    "      e.salary = (SELECT MAX(e2.salary) " +
                    "                  FROM Employee e2 " +
                    "                  WHERE e2.department = :dept)")
})
public class Employee {

例子

以下代码来自Employee.java。

package cn..common;



import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
@Entity
@NamedQueries({
  @NamedQuery(name="findEmployeesAboveSal",
              query="SELECT e " +
                    "FROM Employee e " +
                    "WHERE e.department = :dept AND " +
                    "      e.salary > :sal"),
  @NamedQuery(name="findHighestPaidByDepartment",
              query="SELECT e " +
                    "FROM Employee e " +
                    "WHERE e.department = :dept AND " +
                    "      e.salary = (SELECT MAX(e2.salary) " +
                    "                  FROM Employee e2 " +
                    "                  WHERE e2.department = :dept)")
})
public class Employee {
    @Id
    private int id;
    private String name;
    private long salary;
    @Temporal(TemporalType.DATE)
    private Date startDate;
    
    @ManyToOne
    private Employee manager;
    
    @OneToMany(mappedBy="manager")
    private Collection<Employee> directs;

    @ManyToOne
    private Department department;
    
    @ManyToMany 
    private Collection<Project> projects;

    public Employee() {
        projects = new ArrayList<Project>();
        directs = new ArrayList<Employee>();
    }

    public void setId(int id) {
      this.id = id;
    }

    public void setName(String name) {
      this.name = name;
    }

    public void setSalary(long salary) {
      this.salary = salary;
    }

    public void setStartDate(Date startDate) {
      this.startDate = startDate;
    }

    public void setManager(Employee manager) {
      this.manager = manager;
    }

    public void setDirects(Collection<Employee> directs) {
      this.directs = directs;
    }

    public void setDepartment(Department department) {
      this.department = department;
    }

    public void setProjects(Collection<Project> projects) {
      this.projects = projects;
    }

    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }

    public long getSalary() {
        return salary;
    }

    public Date getStartDate() {
        return startDate;
    }
    
    public Department getDepartment() {
        return department;
    }
    
    public Collection<Employee> getDirects() {
        return directs;
    }
    
    public Employee getManager() {
        return manager;
    }

    public Collection<Project> getProjects() {
        return projects;
    }
    
    public String toString() {
        return "Employee " + getId() + 
               ": name: " + getName() +
               ", salary: " + getSalary() +
               ", dept: " + ((getDepartment() == null) ? null : getDepartment().getName());
    }
}

以下代码来自Project.java。

package cn..common;


import java.util.ArrayList;
import java.util.Collection;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

@Entity
public class Project {
    @Id
    protected int id;
    protected String name;
    @ManyToMany(mappedBy="projects")
    private Collection<Employee> employees;

    public Project() {
        employees = new ArrayList<Employee>();
    }

    public void setId(int id) {
      this.id = id;
    }

    public void setName(String name) {
      this.name = name;
    }

    public void setEmployees(Collection<Employee> employees) {
      this.employees = employees;
    }

    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    
    public Collection<Employee> getEmployees() {
        return employees;
    }
    
    public String toString() {
        return "Project id: " + getId() + ", name: " + getName();
    }
}

下面的代码来自Department.java。

package cn..common;


import java.util.ArrayList;
import java.util.Collection;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Department {
    @Id
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    private Collection<Employee> employees;

    public Department() {
        employees = new ArrayList<Employee>();
    }
    
    public void setId(int id) {
      this.id = id;
    }

    public void setName(String name) {
      this.name = name;
    }

    public void setEmployees(Collection<Employee> employees) {
      this.employees = employees;
    }

    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    
    public Collection<Employee> getEmployees() {
        return employees;
    }

    public String toString() {
        return "Department no: " + getId() + 
               ", name: " + getName();
    }
}

下面的代码来自PersonDaoImpl.java。

package cn..common;

import java.util.Collection;
import java.util.Date;

import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.PersistenceContext;
import javax.persistence.TemporalType;

import org.springframework.transaction.annotation.Transactional;

@Transactional
public class PersonDaoImpl {
  public void test() {
    Employee emp = new Employee();
    emp.setName("Tom");
    emp.setSalary(123);
    emp.setStartDate(new Date());
    emp.setId(1);

    Project pro = new Project();
    pro.setName("Design");
    pro.getEmployees().add(emp);

    Department dept = new Department();
    dept.setName("Dept");
    dept.getEmployees().add(emp);

    emp.setDepartment(dept);
    emp.getProjects().add(pro);

    em.persist(dept);
    em.persist(pro);
    em.persist(emp);

    String deptName = "Dept";
    String empName = "Tom";


  }
  public Collection<Employee> findEmployeesHiredDuringPeriod(Date start, Date end) {
      return (Collection<Employee>) 
          em.createQuery("SELECT e " +
                         "FROM Employee e " +
                         "WHERE e.startDate BETWEEN :start AND :end")
            .setParameter("start", start, TemporalType.DATE)
            .setParameter("end", end, TemporalType.DATE)
            .getResultList();
  }

  public Employee findHighestPaidByDepartment(Department dept) {
      try {
          return (Employee) em.createNamedQuery("findHighestPaidByDepartment")
                              .setParameter("dept", dept)
                              .getSingleResult();
      } catch (NoResultException e) {
          return null;
      }
  }

  public Collection<Employee> findAllEmployees() {
      return (Collection<Employee>) em.createQuery(
              "SELECT e FROM Employee e").getResultList();
  }
  @PersistenceContext
  private EntityManager em;
}
下载 Named_Query_ParamTypes.zip

以下是数据库转储。

Table Name: DEPARTMENT
 Row:
    Column Name: ID,
    Column Type: INTEGER:
    Column Value: 0

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Dept





Table Name: EMPLOYEE
 Row:
    Column Name: ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Tom

    Column Name: SALARY,
    Column Type: BIGINT:
    Column Value: 123

    Column Name: STARTDATE,
    Column Type: DATE:
    Column Value: 2014-12-29

    Column Name: DEPARTMENT_ID,
    Column Type: INTEGER:
    Column Value: 0

    Column Name: MANAGER_ID,
    Column Type: INTEGER:
    Column Value: null





Table Name: EMPLOYEE_PROJECT
 Row:
    Column Name: EMPLOYEES_ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: PROJECTS_ID,
    Column Type: INTEGER:
    Column Value: 0





Table Name: PROJECT
 Row:
    Column Name: ID,
    Column Type: INTEGER:
    Column Value: 0

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Design


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