Hibernate快速入門

Hibernate是一個開源，輕量級的ORM(對象關(guān)系映射)工具。Hibernate框架簡化了java應(yīng)用程序與數(shù)據(jù)庫交互的開發(fā)。

ORM工具簡化了數(shù)據(jù)創(chuàng)建，數(shù)據(jù)處理和數(shù)據(jù)訪問。它是將對象映射到數(shù)據(jù)庫中存儲的數(shù)據(jù)(表)的編程技術(shù)。

注：為什么會有這篇教程文章？答：只是想寫一篇最NB的Hibernate教程入門文章。NB代表人見人愛，花見花開，車見爆胎,飛鳥落地…，最后，需要注意的是：這篇文章包教不包會！除非你從頭到尾認真看完并運行所有示例代碼。

1. Hibernate快速入門簡介

本教程文章基于以下工具(軟件)：

• Hibernate 5.2.2.Final
• Eclipse 4.6 (MARS)

Hibernate.x ~ Hibernate.5 更新功能：

1. 從Hibernate 5.0開始Hibernate Spatial是Hibernate項目的一部分，因此我們也可以處理GIS數(shù)據(jù)了。

2. 域模型映射支持Java 8日期和時間類型。 標準SQL日期/時間類型以及支持的Java 8 Date / Time類類型之間的映射，如下所示：

   • DATE: java.time.LocalDate
   • TIME: java.time.LocalTime, java.time.OffsetTime
   • TIMESTAMP: java.time.Instant, java.time.LocalDateTime,java.time.OffsetDateTime 和 java.time.ZonedDateTime

3. 字節(jié)碼增強機制從頭重新設(shè)計，Hibernate可支持Maven和Gradle插件?？梢酝ㄟ^字節(jié)碼儀器來增強三個主要方面：

   • 懶初始化：字段可以聲明為LAZY，只有在第一次被訪問時，它們才被提取。
   • 臟檢查：實體被增強，使得它們可以跟蹤在持久化上下文中加載之后變化的所有屬性。
   • 雙向關(guān)聯(lián)：即使開發(fā)人員僅更新單側(cè)，但也可以自動同步雙向關(guān)聯(lián)的雙方。

4. Hibernate的原生API(Session等)已更新為使用泛型類型化。無需在獲取實體時轉(zhuǎn)換。

5. Hibernate 5.0將其擴展到更廣泛的類型(例如UUID)。
6. 引用二級緩存，使實體引用能夠直接存儲到第二級緩存中(用于不可變實體)。

2. 準備數(shù)據(jù)庫

Hibernate是一個庫，為了處理所有類型的數(shù)據(jù)庫，它不依賴于應(yīng)用程序選擇的任何類型的數(shù)據(jù)庫，如果Java是“一次寫入到處運行”的語言，Hibernate則是“寫一次就可運行在所有類型的數(shù)據(jù)庫“中的框架。

在這篇文章中，使用的是MySQL數(shù)據(jù)(你可使用其它的數(shù)據(jù)庫，如：Oracle，MySQL或SQL Server)，并創(chuàng)建一個簡單的數(shù)據(jù)庫：mydb，完整的數(shù)據(jù)庫創(chuàng)建語句如下所示：

創(chuàng)建數(shù)據(jù)：

CREATE DATABASE IF NOT EXISTS mydb default charset utf8 COLLATE utf8_general_ci;

需要創(chuàng)建以下幾張表，它們的關(guān)系圖如下所示 -

創(chuàng)建表語句：

create table DEPARTMENT (
   DEPT_ID integer not null,
   DEPT_NAME varchar(255) not null,
   DEPT_NO varchar(20) not null,
   LOCATION varchar(255),
   primary key (DEPT_ID),
   unique (DEPT_NO)
);

create table EMPLOYEE (
   EMP_ID bigint not null,
   EMP_NAME varchar(50) not null,
   EMP_NO varchar(20) not null,
   HIRE_DATE date not null,
   IMAGE longblob,
   JOB varchar(30) not null,
   SALARY float not null,
   DEPT_ID integer not null,
   MNG_ID bigint,
   primary key (EMP_ID),
   unique (EMP_NO)
);

create table SALARY_GRADE (
   GRADE integer not null,
   HIGH_SALARY float not null,
   LOW_SALARY float not null,
   primary key (GRADE)
);

create table TIMEKEEPER (
   Timekeeper_Id varchar(36) not null,
   Date_Time datetime not null,
   In_Out char(1) not null,
   EMP_ID bigint not null,
   primary key (Timekeeper_Id)
);

alter table EMPLOYEE
   add index FK75C8D6AE269A3C9 (DEPT_ID),
   add constraint FK75C8D6AE269A3C9
   foreign key (DEPT_ID)
   references DEPARTMENT (DEPT_ID);

alter table EMPLOYEE
   add index FK75C8D6AE6106A42 (EMP_ID),
   add constraint FK75C8D6AE6106A42
   foreign key (EMP_ID)
   references EMPLOYEE (EMP_ID);

alter table EMPLOYEE
   add index FK75C8D6AE13C12F64 (MNG_ID),
   add constraint FK75C8D6AE13C12F64
   foreign key (MNG_ID)
   references EMPLOYEE (EMP_ID);

alter table TIMEKEEPER
   add index FK744D9BFF6106A42 (EMP_ID),
   add constraint FK744D9BFF6106A42
   foreign key (EMP_ID)
   references EMPLOYEE (EMP_ID);

向上面創(chuàng)建的表中，分別插入一些測試數(shù)據(jù)，如下所示 -

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (10, 'ACCOUNTING', 'D10', 'NEW YORK');

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (20, 'RESEARCH', 'D20', 'DALLAS');

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (30, 'SALES', 'D30', 'CHICAGO');

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (40, 'OPERATIONS', 'D40', 'BOSTON');

-------------------------------------------------------------------------------------------------


insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7839, 'KING', 'E7839', Str_To_Date('17-11-1981', '%d-%m-%Y'), 'PRESIDENT', 5000, 10, null);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7566, 'JONES', 'E7566', Str_To_Date('02-04-1981', '%d-%m-%Y'), 'MANAGER', 2975, 20, 7839);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7902, 'FORD', 'E7902', Str_To_Date('03-12-1981', '%d-%m-%Y'), 'ANALYST', 3000, 20, 7566);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7369, 'SMITH', 'E7369', Str_To_Date('17-12-1980', '%d-%m-%Y'), 'CLERK', 800, 20, 7902);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7698, 'BLAKE', 'E7698', Str_To_Date('01-05-1981', '%d-%m-%Y'), 'MANAGER', 2850, 30, 7839);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7499, 'ALLEN', 'E7499', Str_To_Date('20-02-1981', '%d-%m-%Y'), 'SALESMAN', 1600, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7521, 'WARD', 'E7521', Str_To_Date('22-02-1981', '%d-%m-%Y'), 'SALESMAN', 1250, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7654, 'MARTIN', 'E7654', Str_To_Date('28-09-1981', '%d-%m-%Y'), 'SALESMAN', 1250, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7782, 'CLARK', 'E7782', Str_To_Date('09-06-1981', '%d-%m-%Y'), 'MANAGER', 2450, 30, 7839);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7788, 'SCOTT', 'E7788', Str_To_Date('19-04-1987', '%d-%m-%Y'), 'ANALYST', 3000, 20, 7566);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7844, 'TURNER', 'E7844', Str_To_Date('08-09-1981', '%d-%m-%Y'), 'SALESMAN', 1500, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7876, 'ADAMS', 'E7876', Str_To_Date('23-05-1987', '%d-%m-%Y'), 'CLERK', 1100, 20, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7900, 'ADAMS', 'E7900', Str_To_Date('03-12-1981', '%d-%m-%Y'), 'CLERK', 950, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7934, 'MILLER', 'E7934', Str_To_Date('23-01-1982', '%d-%m-%Y'), 'CLERK', 1300, 10, 7698);

-------------------------------------------------------------------------------------------------

insert into Salary_Grade (GRADE, HIGH_SALARY, LOW_SALARY)
values (1, 9999, 3001);

3. 創(chuàng)建Maven項目和聲明庫

在這里，創(chuàng)建一個Maven項目并在pom.xml中聲明使用的Hibernate庫。打開 Eclipse，選擇菜單 File -> New -> Other…，在彈出框中選擇 Maven，如下所示 -

下一步選擇工作目錄，如下圖所示 -

下一步，選擇模板類型，如下圖所示 -

下一步，寫入工程名稱：HibernateQuickStart，以及輸入包信息：com.yiibai 等信息。

項目(HibernateQuickStart)創(chuàng)建完成后，如下圖所示 -

在pom.xml中，需要聲明使用Hibernate 5庫，以及用于各種數(shù)據(jù)庫類型(如Oracle，MySQL和SQL Server)的JDBC庫，這里使用 MySQL JDBC。

完整的 pom.xml 配置/聲明如下所示 -

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.yiibai</groupId>
    <artifactId>HibernateQuickStart</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>HibernateQuickStart</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Hibernate Core -->
        <!-- http://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.2.Final</version>
        </dependency>


        <!-- MySQL JDBC driver -->
        <!-- http://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
        </dependency>

        <!-- SQLServer JDBC driver (JTDS) -->
        <!-- http://mvnrepository.com/artifact/net.sourceforge.jtds/jtds -->
        <dependency>
            <groupId>net.sourceforge.jtds</groupId>
            <artifactId>jtds</artifactId>
            <version>1.3.1</version>
        </dependency>
    </dependencies>
</project>

4. 實體類

在這一步中，我們來創(chuàng)建實體類。每個實體描述一個數(shù)據(jù)庫中的表。這里先不說明每個類是做什么用的。一共要創(chuàng)建如下幾個實體類(對應(yīng)上面創(chuàng)建的四張表)，如下 -

• Department.java
• Employee.java
• SalaryGrade.java
• Timekeeper.java

所有創(chuàng)建的類如下圖所示 -

這幾個類的代碼，分別如下所示 -

Department.java 類代碼 -

package com.yiibai.entities;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "DEPARTMENT", uniqueConstraints = { @UniqueConstraint(columnNames = { "DEPT_NO" }) })
public class Department {

    private Integer deptId;
    private String deptNo;

    private String deptName;
    private String location;
    private Set<Employee> employees = new HashSet<Employee>(0);

    public Department() {
    }

    public Department(Integer deptId, String deptName, String location) {
        this.deptId = deptId;
        this.deptNo = "D" + this.deptId;
        this.deptName = deptName;
        this.location = location;
    }

    @Id
    @Column(name = "DEPT_ID")
    public Integer getDeptId() {
        return deptId;
    }

    public void setDeptId(Integer deptId) {
        this.deptId = deptId;
    }

    @Column(name = "DEPT_NO", length = 20, nullable = false)
    public String getDeptNo() {
        return deptNo;
    }

    public void setDeptNo(String deptNo) {
        this.deptNo = deptNo;
    }

    @Column(name = "DEPT_NAME", nullable = false)
    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    @Column(name = "LOCATION")
    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "department")
    public Set<Employee> getEmployees() {
        return employees;
    }

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

Employee.java 類代碼 -

package com.yiibai.entities;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "EMPLOYEE", uniqueConstraints = { @UniqueConstraint(columnNames = { "EMP_NO" }) })
public class Employee {
    private Long empId;
    private String empNo;

    private String empName;
    private String job;
    private Employee manager;
    private Date hideDate;
    private Float salary;
    private byte[] image;

    private Department department;
    private Set<Employee> employees = new HashSet<Employee>(0);

    public Employee() {
    }

    public Employee(Long empId, String empName, String job, Employee manager, Date hideDate, Float salary, Float comm,
            Department department) {
        this.empId = empId;
        this.empNo = "E" + this.empId;
        this.empName = empName;
        this.job = job;
        this.manager = manager;
        this.hideDate = hideDate;
        this.salary = salary;
        this.department = department;
    }

    @Id
    @Column(name = "EMP_ID")
    public Long getEmpId() {
        return empId;
    }

    public void setEmpId(Long empId) {
        this.empId = empId;
    }

    @Column(name = "EMP_NO", length = 20, nullable = false)
    public String getEmpNo() {
        return empNo;
    }

    public void setEmpNo(String empNo) {
        this.empNo = empNo;
    }

    @Column(name = "EMP_NAME", length = 50, nullable = false)
    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    @Column(name = "JOB", length = 30, nullable = false)
    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "MNG_ID")
    public Employee getManager() {
        return manager;
    }

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

    @Column(name = "HIRE_DATE", nullable = false)
    @Temporal(TemporalType.DATE)
    public Date getHideDate() {
        return hideDate;
    }

    public void setHideDate(Date hideDate) {
        this.hideDate = hideDate;
    }

    @Column(name = "SALARY", nullable = false)
    public Float getSalary() {
        return salary;
    }

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

    @Column(name = "IMAGE", length = 1111111, nullable = true)
    @Lob
    public byte[] getImage() {
        return image;
    }

    public void setImage(byte[] image) {
        this.image = image;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "DEPT_ID", nullable = false)
    public Department getDepartment() {
        return department;
    }

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

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "empId")
    public Set<Employee> getEmployees() {
        return employees;
    }

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

}

SalaryGrade.java 類代碼 -

package com.yiibai.entities;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "SALARY_GRADE")
public class SalaryGrade {
    private Integer grade;
    private Float lowSalary;
    private Float highSalary;

    public SalaryGrade() {
    }

    public SalaryGrade(Integer grade, Float lowSalary, Float highSalary) {
        this.grade = grade;
        this.lowSalary = lowSalary;
        this.highSalary = highSalary;
    }

    @Id
    @Column(name = "GRADE")
    public Integer getGrade() {
        return grade;
    }

    public void setGrade(Integer grade) {
        this.grade = grade;
    }

    @Column(name = "LOW_SALARY", nullable = false)
    public Float getLowSalary() {
        return lowSalary;
    }

    public void setLowSalary(Float lowSalary) {
        this.lowSalary = lowSalary;
    }

    @Column(name = "HIGH_SALARY", nullable = false)
    public Float getHighSalary() {
        return highSalary;
    }

    public void setHighSalary(Float highSalary) {
        this.highSalary = highSalary;
    }
}

Timekeeper.java 類代碼 -

package com.yiibai.entities;

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "TIMEKEEPER")
public class Timekeeper {
    public static final char IN = 'I';
    public static final char OUT = 'O';

    private String timekeeperId;

    private Date dateTime;

    private Employee employee;

    // 'I' or 'O'
    private char inOut;

    @Id
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid2")
    @Column(name = "Timekeeper_Id", length = 36)
    public String getTimekeeperId() {
        return timekeeperId;
    }

    public void setTimekeeperId(String timekeeperId) {
        this.timekeeperId = timekeeperId;
    }

    @Column(name = "Date_Time", nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    public Date getDateTime() {
        return dateTime;
    }

    public void setDateTime(Date dateTime) {
        this.dateTime = dateTime;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "EMP_ID", nullable = false)
    public Employee getEmployee() {
        return employee;
    }

    public void setEmployee(Employee employee) {
        this.employee = employee;
    }

    @Column(name = "In_Out", nullable = false, length = 1)
    public char getInOut() {
        return inOut;
    }

    public void setInOut(char inOut) {
        this.inOut = inOut;
    }

}

5. 配置hibernate

配置hibernate目的是讓Hibernate可以連接數(shù)據(jù)庫并與數(shù)據(jù)庫交互，并聲明在前面的步驟中創(chuàng)建的實體列表。

在src/main/java中創(chuàng)建一個名稱為：hibernate.cfg.xml 的配置文件，當前項目結(jié)構(gòu)如下圖所示 -

hibernate.cfg.xml 配置文件的內(nèi)容如下所示 -

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

  <session-factory>
      <!-- Database connection settings -->
      <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
      <property name="connection.url">jdbc:mysql://localhost:3306/mydb?serverTimezone=UTC</property>
      <property name="connection.username">root</property>
      <property name="connection.password">123456</property>

      <!-- JDBC connection pool (use the built-in) -->
      <property name="connection.pool_size">1</property>

      <!-- SQL dialect -->
      <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

      <!-- Enable Hibernate's automatic session context management -->
      <property name="current_session_context_class">thread</property>

      <!-- Disable the second-level cache -->
      <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>

      <!-- Echo all executed SQL to stdout -->
      <property name="show_sql">true</property>

      <mapping class="com.yiibai.entities.Department" />
      <mapping class="com.yiibai.entities.Employee" />
      <mapping class="com.yiibai.entities.SalaryGrade" />
      <mapping class="com.yiibai.entities.Timekeeper" />

  </session-factory>

</hibernate-configuration>

每種數(shù)據(jù)庫都有一個單獨的方言， 例如：

Oracle方言：

• org.hibernate.dialect.Oracle10gDialect(Dùngcho 10g＆11g)
• org.hibernate.dialect.Oracle12cDialect

SQL Server方言：

• org.hibernate.dialect.SQLServerDialect并
• org.hibernate.dialect.SQLServer2012Dialect
• org.hibernate.dialect.SQLServer2008Dialect

MySQL方言

• org.hibernate.dialect.MySQLDialect
• org.hibernate.dialect.MySQL5Dialect

什么是方言？

Dialect是一個使用Hibernate的方式將數(shù)據(jù)庫的數(shù)據(jù)類型轉(zhuǎn)換為Java的數(shù)據(jù)類型，反之亦然。此外，它用于定義將HSQL(Hibernate SQL)的函數(shù)轉(zhuǎn)換為數(shù)據(jù)中的函數(shù)的方式，如下列出的一部分 -

6. SessionFactory

創(chuàng)建一個文件： HibernateUtils.java ， 其代碼如下 -

7. Hibernate查詢語言(HQL)

Hibernate使用Hibernate查詢語言(HQL)查詢數(shù)據(jù)。 HQL與我們所了解的數(shù)據(jù)庫SQL語句有點不同。

SQL：

• 在表中查詢數(shù)據(jù)

HQL：

• 在實體類中查詢對象數(shù)據(jù)

參考比較以下用法 -

-- SQL
-- This is a SQL query in table DEPARTMENT.
Select d.DEPT_NO, d.DEPT_NAME from DEPARTMENT d;

-- HQL
-- This is a HQL query in Entity Department.
Select d.deptNo, d.deptName from Department d;

-- Query Object
Select d from Department d;

Hibernate的操作規(guī)則：

應(yīng)用程序編寫的HQL在操作過程中，Hibernate本身就意識到它使用的數(shù)據(jù)庫類型(如：MySQL)，它會自動將HQL轉(zhuǎn)換為等價的數(shù)據(jù)庫類型的SQL形式。 事實上，各種類型的數(shù)據(jù)庫之間的SQL語法有一些差異，比如：返回記錄的行數(shù)的限制就不同(MySQL中使用 limit 子句)。

可以參考HQL語法： http://docs.jboss.org/hibernate/orm/3.6/reference/en-US/html/queryhql.html

8. 使用Hibernate查詢數(shù)據(jù)

在Hibernate中有很多方法可以用來查詢數(shù)據(jù)。在這部分中，將介紹一些查詢數(shù)據(jù)的典型方法。

8.1 - 使用HQL的查詢對象

查詢對象示例-1
第一個例子，使用HQL查詢對象(Entity)，創(chuàng)建一個Java類文件：QueryObjectDemo.java，其代碼如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class QueryObjectDemo {

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();

       try {

           // All the action with DB via Hibernate
           // must be located in one transaction.
           // Start Transaction.            
           session.getTransaction().begin();

           // Create an HQL statement, query the object.
           // Equivalent to the SQL statement:
           // Select e.* from EMPLOYEE e order by e.EMP_NAME, e.EMP_NO
           String sql = "Select e from " + Employee.class.getName() + " e "
                   + " order by e.empName, e.empNo ";


           // Create Query object.
           Query<Employee> query = session.createQuery(sql);


           // Execute query.
           List<Employee> employees = query.getResultList();

           for (Employee emp : employees) {
               System.out.println("Emp: " + emp.getEmpNo() + " : "
                       + emp.getEmpName());
           }

           // Commit data.
           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           // Rollback in case of an error occurred.
           session.getTransaction().rollback();
       }
   }

}

運行上面代碼，得到以下結(jié)果 -

查詢對象示例-2

創(chuàng)建一個Java類文件：QueryObjectDemo2.java，其代碼如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class QueryObjectDemo2 {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {

            // All the action with DB via Hibernate
            // must be located in one transaction
            // Start Transaction.
            session.getTransaction().begin();

            // Create an HQL statement, query the object.
            // HQL with parameters.
            // Equivalent to the SQL statement:
            // Select e.* from EMPLOYEE e cross join DEPARTMENT d
            // where e.DEPT_ID = d.DEPT_ID and d.DEPT_NO = :deptNo;
            String sql = "Select e from " + Employee.class.getName() + " e " + " where e.department.deptNo=:deptNo ";

            // Create query object.
            Query<Employee> query = session.createQuery(sql);

            query.setParameter("deptNo", "D10");

            // Execute query.
            List<Employee> employees = query.getResultList();

            for (Employee emp : employees) {
                System.out.println("Emp: " + emp.getEmpNo() + " : " + emp.getEmpName());
            }

            // Commit data
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }
    }
}

運行上面代碼，得到以下結(jié)果 -

......
org.hibernate.hql.internal.QueryTranslatorFactoryInitiator initiateService
INFO: HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select employee0_.EMP_ID ..._NO=?
Emp: E7839 : KING
Emp: E7934 : MILLER
`

8.2 - 使用HQL查詢讀取多列數(shù)據(jù)

創(chuàng)建一個Java類文件：QuerySomeColumnDemo.java，其代碼如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class QuerySomeColumnDemo {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();

            // Query some columns.
            String sql = "Select e.empId, e.empNo, e.empName from "
                    + Employee.class.getName() + " e ";

            Query<Object[]> query = session.createQuery(sql);

            // Execute Query.
            // Get the array of Object
            List<Object[]> datas = query.getResultList();

            for (Object[] emp : datas) {
                System.out.println("Emp Id: " + emp[0]);
                System.out.println("    Emp No: " + emp[1]);
                System.out.println("    Emp Name: " + emp[2]);
            }

            // Commit data.
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }

    }
}

運行上面代碼，得到以下結(jié)果 -

Hibernate: select employee0_.EMP_ID..._0_ from EMPLOYEE employee0_
Emp Id: 7369
    Emp No: E7369
    Emp Name: SMITH
Emp Id: 7499
    Emp No: E7499
    Emp Name: ALLEN
Emp Id: 7521
    Emp No: E7521
    Emp Name: WARD
Emp Id: 7566
    Emp No: E7566
    Emp Name: JONES
Emp Id: 7654
    Emp No: E7654
    Emp Name: MARTIN
Emp Id: 7698
    Emp No: E7698
    Emp Name: BLAKE
Emp Id: 7782
    Emp No: E7782
    Emp Name: CLARK
Emp Id: 7788
    Emp No: E7788
    Emp Name: SCOTT
Emp Id: 7839
    Emp No: E7839
    Emp Name: KING
Emp Id: 7844
    Emp No: E7844
    Emp Name: TURNER
Emp Id: 7876
    Emp No: E7876
    Emp Name: ADAMS
Emp Id: 7900
    Emp No: E7900
    Emp Name: ADAMS
Emp Id: 7902
    Emp No: E7902
    Emp Name: FORD
Emp Id: 7934
    Emp No: E7934
    Emp Name: MILLER
`

8.3 - 使用HQL和JavaBean查詢多列數(shù)據(jù)

在這種情況下，如果需要在某些表中提取某些列的數(shù)據(jù)，最好的方法是使用Java bean。使用Java bean的構(gòu)造函數(shù)來為不同的字段設(shè)置值。在此構(gòu)造函數(shù)加入HQL查詢。