本文是Hibernate Native SQL查询示例教程，介绍了Hibernate通过SQLQuery对象执行本机SQL查询的方法，包括单表、多表、实体和Join查询，以及带参数查询。还提到使用addScalar方法定义列数据类型可提升性能，若非执行特定数据库查询，应避免使用。
Hibernate Native SQL查询示例
欢迎使用Hibernate Native SQL Query示例教程。我们在前面的文章中研究了Hibernate查询语言和Hibernate Criteria，今天我们将通过示例来研究Hibernate Native SQL查询。
目录[ 隐藏 ]
Hibernate SQL查询
Hibernate提供了通过使用SQLQuery对象来执行本机SQL查询的选项。当我们必须执行Hibernate API不支持的数据库供应商特定查询时，Hibernate SQL Query非常方便。例如查询提示或Oracle数据库中的CONNECT关键字。
对于正常情况，Hibernate SQL查询不是推荐的方法，因为我们放弃了与hibernate关联和hibernate一级缓存相关的好处。
我将使用MySQL数据库以及与HQL示例中使用的相同的表和数据设置，因此您应该首先了解表和相应的模型类映射。
Hibernate Native SQL示例
对于Hibernate Native SQL Query，我们使用Session.createSQLQuery(String query)创建SQLQuery对象并执行它。例如，如果要读取Employee表中的所有记录，我们可以通过下面的代码来完成。
// Prep work
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.getCurrentSession();
// Get All Employees
Transaction tx = session.beginTransaction();
SQLQuery query = session.createSQLQuery("select emp_id, emp_name, emp_salary from Employee");
List<Object[]> rows = query.list();
for(Object[] row : rows){
Employee emp = new Employee();
emp.setId(Long.parseLong(row[0].toString()));
emp.setName(row[1].toString());
emp.setSalary(Double.parseDouble(row[2].toString()));
System.out.println(emp);
}
当我们为我们的数据设置执行上面的代码时，它产生以下输出。
Hibernate: select emp_id, emp_name, emp_salary from Employee
Id= 1, Name= Pankaj, Salary= 100.0, {Address= null}
Id= 2, Name= David, Salary= 200.0, {Address= null}
Id= 3, Name= Lisa, Salary= 300.0, {Address= null}
Id= 4, Name= Jack, Salary= 400.0, {Address= null}
请注意，该list()方法返回List of Object数组，我们需要将它们显式解析为double，long等。我们的Employee和Address类具有以下toString()方法实现。
@Override
public String toString() {
return "Id= " + id + ", Name= " + name + ", Salary= " + salary
+ ", {Address= " + address + "}";
}
@Override
public String toString() {
return "AddressLine1= " + addressLine1 + ", City=" + city
+ ", Zipcode=" + zipcode;
}
请注意，我们的查询不返回地址数据，而如果我们使用HQL查询"from Employee"，它也会返回关联的表数据。
Hibernate SQL Query addScalar
Hibernate用来ResultSetMetadata推断查询返回的列的类型，从性能的角度来看我们可以使用addScalar()方法来定义列的数据类型。但是我们仍然会以Object数组的形式获取数据。
//Get All Employees - addScalar example
query = session.createSQLQuery("select emp_id, emp_name, emp_salary from Employee")
.addScalar("emp_id", new LongType())
.addScalar("emp_name", new StringType())
.addScalar("emp_salary", new DoubleType());
rows = query.list();
for(Object[] row : rows){
Employee emp = new Employee();
emp.setId(Long.parseLong(row[0].toString()));
emp.setName(row[1].toString());
emp.setSalary(Double.parseDouble(row[2].toString()));
System.out.println(emp);
}
生成的输出将是相同的，但是当数据量很大时，我们会看到性能略有提升。
Hibernate Native SQL多表
如果我们想从Employee和Address表中获取数据，我们可以简单地为其编写SQL查询并解析结果集。
query = session.createSQLQuery("select e.emp_id, emp_name, emp_salary,address_line1, city,
zipcode from Employee e, Address a where a.emp_id=e.emp_id");
rows = query.list();
for(Object[] row : rows){
Employee emp = new Employee();
emp.setId(Long.parseLong(row[0].toString()));
emp.setName(row[1].toString());
emp.setSalary(Double.parseDouble(row[2].toString()));
Address address = new Address();
address.setAddressLine1(row[3].toString());
address.setCity(row[4].toString());
address.setZipcode(row[5].toString());
emp.setAddress(address);
System.out.println(emp);
}
对于上面的代码，产生的输出将如下所示。
Hibernate: select e.emp_id, emp_name, emp_salary,address_line1, city, zipcode from Employee e, Address a where a.emp_id=e.emp_id
Id= 1, Name= Pankaj, Salary= 100.0, {Address= AddressLine1= Albany Dr, City=San Jose, Zipcode=95129}
Id= 2, Name= David, Salary= 200.0, {Address= AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051}
Id= 3, Name= Lisa, Salary= 300.0, {Address= AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100}
Id= 4, Name= Jack, Salary= 400.0, {Address= AddressLine1= City Centre, City=New Delhi, Zipcode=100100}
Hibernate Native SQL实体和Join
我们还可以使用addEntity()和addJoin()方法使用表连接从关联表中获取数据。例如，也可以如下检索上述数据。
//Join example with addEntity and addJoin
query = session.createSQLQuery("select {e.*}, {a.*} from Employee e join Address a ON e.emp_id=a.emp_id")
.addEntity("e",Employee.class)
.addJoin("a","e.address");
rows = query.list();
for (Object[] row : rows) {
for(Object obj : row) {
System.out.print(obj + "::");
}
System.out.println("\n");
}
//Above join returns both Employee and Address Objects in the array
for (Object[] row : rows) {
Employee e = (Employee) row[0];
System.out.println("Employee Info::"+e);
Address a = (Address) row[1];
System.out.println("Address Info::"+a);
}
{[aliasname].*}用于返回实体的所有属性。当我们使用addEntity()和addJoin()上面的连接查询时，它返回两个对象，如上所示。
上面代码产生的输出如下。
Hibernate: select e.emp_id as emp_id1_1_0_, e.emp_name as emp_name2_1_0_, e.emp_salary as emp_sala3_1_0_, a.emp_id as emp_id1_0_1_, a.address_line1 as address_2_0_1_, a.city as city3_0_1_, a.zipcode as zipcode4_0_1_ from Employee e join Address a ON e.emp_id=a.emp_id
Id= 1, Name= Pankaj, Salary= 100.0, {Address= AddressLine1= Albany Dr, City=San Jose, Zipcode=95129}::AddressLine1= Albany Dr, City=San Jose, Zipcode=95129::
Id= 2, Name= David, Salary= 200.0, {Address= AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051}::AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051::
Id= 3, Name= Lisa, Salary= 300.0, {Address= AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100}::AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100::
Id= 4, Name= Jack, Salary= 400.0, {Address= AddressLine1= City Centre, City=New Delhi, Zipcode=100100}::AddressLine1= City Centre, City=New Delhi, Zipcode=100100::
Employee Info::Id= 1, Name= Pankaj, Salary= 100.0, {Address= AddressLine1= Albany Dr, City=San Jose, Zipcode=95129}
Address Info::AddressLine1= Albany Dr, City=San Jose, Zipcode=95129
Employee Info::Id= 2, Name= David, Salary= 200.0, {Address= AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051}
Address Info::AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051
Employee Info::Id= 3, Name= Lisa, Salary= 300.0, {Address= AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100}
Address Info::AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100
Employee Info::Id= 4, Name= Jack, Salary= 400.0, {Address= AddressLine1= City Centre, City=New Delhi, Zipcode=100100}
Address Info::AddressLine1= City Centre, City=New Delhi, Zipcode=100100
您可以在mysql客户端中运行这两个查询，并注意生成的输出是相同的。
mysql> select e.emp_id as emp_id1_1_0_, e.emp_name as emp_name2_1_0_, e.emp_salary as emp_sala3_1_0_, a.emp_id as emp_id1_0_1_, a.address_line1 as address_2_0_1_, a.city as city3_0_1_, a.zipcode as zipcode4_0_1_ from Employee e join Address a ON e.emp_id=a.emp_id;
+--------------+----------------+----------------+--------------+----------------+-------------+---------------+
| emp_id1_1_0_ | emp_name2_1_0_ | emp_sala3_1_0_ | emp_id1_0_1_ | address_2_0_1_ | city3_0_1_ | zipcode4_0_1_ |
+--------------+----------------+----------------+--------------+----------------+-------------+---------------+
| 1 | Pankaj | 100 | 1 | Albany Dr | San Jose | 95129 |
| 2 | David | 200 | 2 | Arques Ave | Santa Clara | 95051 |
| 3 | Lisa | 300 | 3 | BTM 1st Stage | Bangalore | 560100 |
| 4 | Jack | 400 | 4 | City Centre | New Delhi | 100100 |
+--------------+----------------+----------------+--------------+----------------+-------------+---------------+
4 rows in set (0.00 sec)
mysql> select e.emp_id, emp_name, emp_salary,address_line1, city, zipcode from Employee e, Address a where a.emp_id=e.emp_id;
+--------+----------+------------+---------------+-------------+---------+
| emp_id | emp_name | emp_salary | address_line1 | city | zipcode |
+--------+----------+------------+---------------+-------------+---------+
| 1 | Pankaj | 100 | Albany Dr | San Jose | 95129 |
| 2 | David | 200 | Arques Ave | Santa Clara | 95051 |
| 3 | Lisa | 300 | BTM 1st Stage | Bangalore | 560100 |
| 4 | Jack | 400 | City Centre | New Delhi | 100100 |
+--------+----------+------------+---------------+-------------+---------+
4 rows in set (0.00 sec)
mysql>
带参数的Hibernate Native SQL查询
我们也可以将参数传递给Hibernate SQL查询，就像JDBC PreparedStatement一样。可以使用名称和索引设置参数，如下例所示。
query = session
.createSQLQuery("select emp_id, emp_name, emp_salary from Employee where emp_id = ?");
List<Object[]> empData = query.setLong(0, 1L).list();
for (Object[] row : empData) {
Employee emp = new Employee();
emp.setId(Long.parseLong(row[0].toString()));
emp.setName(row[1].toString());
emp.setSalary(Double.parseDouble(row[2].toString()));
System.out.println(emp);
}
query = session
.createSQLQuery("select emp_id, emp_name, emp_salary from Employee where emp_id = :id");
empData = query.setLong("id", 2L).list();
for (Object[] row : empData) {
Employee emp = new Employee();
emp.setId(Long.parseLong(row[0].toString()));
emp.setName(row[1].toString());
emp.setSalary(Double.parseDouble(row[2].toString()));
System.out.println(emp);
}
上述代码产生的输出将是：
Hibernate: select emp_id, emp_name, emp_salary from Employee where emp_id = ?
Id= 1, Name= Pankaj, Salary= 100.0, {Address= null}
Hibernate: select emp_id, emp_name, emp_salary from Employee where emp_id = ?
Id= 2, Name= David, Salary= 200.0, {Address= null}
这就是Hibernate SQL Query的简要介绍，除非要执行任何特定于数据库的查询，否则应该避免使用它。
转载来源：https://www.journaldev.com/3422/hibernate-native-sql-query-example
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