扩展是指增加通用 Mapper 没有提供的功能。
举例:
通用 Mapper 官方文档中使用一个批量 insert 作为扩展功能的例子: tk.mybatis.mapper.additional.insert.InsertListMapper<T>
tk.mybatis.mapper.additional.insert.InsertListProvider
我们来仿照写一个批量 update。假设我们想生成下面这样的 SQL 语句:
UPDATE tabple_emp SET emp_name=?,emp_age=?,emp_salary=? where emp_id=?;
UPDATE tabple_emp SET emp_name=?,emp_age=?,emp_salary=? where emp_id=?;
UPDATE tabple_emp SET emp_name=?,emp_age=?,emp_salary=? where emp_id=?;
为了生成上面那样的 SQL 语句,我们需要使用到 MyBatis 的 foreach 标签。
<foreach collection="list" item="record" separator=";" >
UPDATE tabple_emp
<set>
emp_name=#{record.empName},
emp_age=#{record.empAge},
emp_salary=#{record.empSalary},
</set>
where emp_id=#{record.empId}
</foreach>
1、创建扩展接口MyBatchUpdateMapper
public interface MyBatchUpdateMapper<T> {
@UpdateProvider(type=MyBatchUpdateProvider.class, method="dynamicSQL")
void batchUpdate(List<T> list);
}
2、创建MyBatchUpdateProvider拼装SQL
public class MyBatchUpdateProvider extends MapperTemplate {
public MyBatchUpdateProvider(Class<?> mapperClass, MapperHelper mapperHelper) {
super(mapperClass, mapperHelper);
}
/**
<foreach collection="list" item="record" separator=";" >
UPDATE tabple_emp
<set>
emp_name=#{record.empName},
emp_age=#{record.empAge},
emp_salary=#{record.empSalary},
</set>
where emp_id=#{record.empId}
</foreach>
*/
public String batchUpdate(MappedStatement statement) {
//1.创建StringBuilder用于拼接SQL语句的各个组成部分
StringBuilder builder = new StringBuilder();
//2.拼接foreach标签
builder.append("<foreach collection=\"list\" item=\"record\" separator=\";\" >");
//3.获取实体类对应的Class对象
Class<?> entityClass = super.getEntityClass(statement);
//4.获取实体类在数据库中对应的表名
String tableName = super.tableName(entityClass);
//5.生成update子句
String updateClause = SqlHelper.updateTable(entityClass, tableName);
builder.append(updateClause);
builder.append("<set>");
//6.获取所有字段信息
Set<EntityColumn> columns = EntityHelper.getColumns(entityClass);
String idColumn = null;
String idHolder = null;
for (EntityColumn entityColumn : columns) {
boolean isPrimaryKey = entityColumn.isId();
//7.判断当前字段是否为主键
if(isPrimaryKey) {
//8.缓存主键的字段名和字段值
idColumn = entityColumn.getColumn();
//※返回格式如:#{record.age,jdbcType=NUMERIC,typeHandler=MyTypeHandler}
idHolder = entityColumn.getColumnHolder("record");
}else {
//9.使用非主键字段拼接SET子句
String column = entityColumn.getColumn();
String columnHolder = entityColumn.getColumnHolder("record");
builder.append(column).append("=").append(columnHolder).append(",");
}
}
builder.append("</set>");
//10.使用前面缓存的主键名、主键值拼接where子句
builder.append("where ").append(idColumn).append("=").append(idHolder);
builder.append("</foreach>");
//11.将拼接好的字符串返回
return builder.toString();
}
}
3、MyMapper继承扩展接口MyBatchUpdateMapper
public interface MyMapper<T>
extends SelectAllMapper<T>,SelectByExampleMapper<T>,MyBatchUpdateMapper<T> {
}
测试:
注意:JDBC要执行分号隔开的SQL语句。必须在连接数据库时添加参数allowMultiQueries=true
public class MyBatchUpdateTest {
public static void main(String[] args) {
ClassPathXmlApplicationContext iocContainer = new ClassPathXmlApplicationContext("spring-context.xml");
EmployeeService employeeService = iocContainer.getBean(EmployeeService.class);
List<Employee> empList = new ArrayList<Employee>();
empList.add(new Employee(25, "newName01", 111.11, 10));
empList.add(new Employee(26, "newName02", 222.22, 20));
empList.add(new Employee(27, "newName03", 333.33, 30));
employeeService.batchUpdateEmp(empList);
iocContainer.close();
}
}
控制台输出:
Preparing: UPDATE tabple_emp SET emp_name=?,emp_salary=?,emp_age=? where emp_id=? ; UPDATE tabple_emp SET emp_name=?,emp_salary=?,emp_age=? where emp_id=? ; UPDATE tabple_emp SET emp_name=?,emp_salary=?,emp_age=? where emp_id=?
Parameters: newName01(String), 111.11(Double), 10(Integer), 1(Integer), newName02(String), 222.22(Double), 20(Integer), 2(Integer), newName03(String), 333.33(Double), 30(Integer), 3(Integer)
Updates: 1