1.動態SQL簡介
動態 SQL是MyBatis強大特性之一.
動態 SQL 元素和使用 JSTL 或其他類似基於 XML 的文本處理器相似.
MyBatis 采用功能強大的基於 OGNL 的表達式來簡化操作.
2.if
1).實現DynamicSQL
public interface EmployeeMapperDynamicSQL {
public List<Employee> getEmpsByCondtionIf(Employee employee);
}
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- 查詢員工:攜帶指定字段查詢條件就帶上該字段的值 -->
<!-- public List<Employee> getEmpsByCondtionIf(Employee employee) -->
<select id="getEmpsByCondtionIf" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<!-- where:根據條件包含 where 子句 -->
where
<!-- test:判斷表達式(OGNL) -->
<!-- OGNL語法參照PPT或者官方文檔:http://commons.apache.org/proper/commons-ognl/language-guide.html -->
<!-- 從參數中取值進行判斷,如果遇到特殊符號去寫轉義字符,查W3C HTML ISO-8859-1 參考手冊 -->
<if test="id!=null">
id=#{id}
</if>
<!-- <if test="lastName!=null and lastName!="""> -->
<!-- <if test="lastName!=null && lastName!=''"> -->
<if test="lastName!=null && lastName!=""">
and last_name like #{lastName}
</if>
<if test="email!=null and email.trim()!=""">
and email=#{email}
</if>
<!-- ognl會進行字符串與數字的轉換判斷 "0"==0 -->
<if test="gender==0 or gender==1">
and gender=#{gender}
</if>
</select>
</mapper>
// select * from tbl_employee WHERE id=? and last_name like ? and email=?
// Employee employee = new Employee(3, "%e%","atguigu@atguigu.com", null);
//select * from tbl_employee WHERE id=? and last_name like ?
Employee employee = new Employee(null, "%e%",null, null);
List<Employee> emps = mapper.getEmpsByCondtionIf(employee);
for(Employee emp:emps) {
System.out.println(emp);
}
2.choose
有時候，我們不想使用所有的條件，而只是想從多個條件中選擇一個使用.針對這種情況，MyBatis 提供了 choose 元素，它有點像 Java 中的 switch 語句.
public List<Employee> getEmpByConditionChoose(Employee employee);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- public List<Employee> getEmpByConditionChoose(Employee employee) -->
<select id="getEmpByConditionChoose" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<where>
<!-- 如果帶了id就用id查，如果帶了lastName就用lastName查;只會進入其中一個 -->
<choose>
<when test="id!=null">
id=#{id}
</when>
<when test="lastName!=null">
last_name like #{lastName}
</when>
<when test="email!=null">
email = #{email}
</when>
<otherwise>
gender = 0
</otherwise>
</choose>
</where>
</select>
</mapper>
//測試choose
Employee employee = new Employee(3, "%e%",null, null);
List<Employee> list = mapper.getEmpByConditionChoose(employee);
for(Employee emp:list) {
System.out.println(emp);
}
3.trim
1).where
public List<Employee> getEmpsByCondtionTrim(Employee employee);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- public List<Employee> getEmpsByCondtionTrim(Employee employee) -->
<select id="getEmpsByCondtionTrim" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<!-- 后面多出的and或者or where標簽不能解決,我們使用trim定制where元素功能 -->
<!-- 自定義字符串的截取規則 -->
<!-- trim:根據條件包含 where 子句 -->
<!-- trim標簽體中是整個字符串拼串 后的結果 -->
<!-- 通過自定義 trim 元素來定制 where 元素的功能 -->
<!-- prefix:前綴;prefix給拼串后的整個字符串加一個前綴 如:where <===> <trim prefix="where"> -->
<!-- prefixOverrides:前綴覆蓋;去掉整個字符串前面多余的字符 -->
<!-- suffix:后綴;suffix給拼串后的整個字符串加一個后綴 -->
<!-- suffixOverrides:后綴覆蓋;去掉整個字符串后面多余的字符 -->
<trim prefix="where" suffixOverrides="and">
<if test="id!=null">
id=#{id} and
</if>
<if test="lastName!=null && lastName!=""">
last_name like #{lastName} and
</if>
<if test="email!=null and email.trim()!=""">
email=#{email} and
</if>
<!-- ognl會進行字符串與數字的轉換判斷 "0"==0 -->
<if test="gender==0 or gender==1">
gender=#{gender}
</if>
</trim>
</select>
</mapper>
@Test
public void testDynamicSql() throws IOException {
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try {
EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
// select * from tbl_employee WHERE id=? and last_name like ? and email=?
// Employee employee = new Employee(3, "%e%","atguigu@atguigu.com", null);
//select * from tbl_employee WHERE id=? and last_name like ?
Employee employee = new Employee(3, "%e%",null, null);
List<Employee> emps = mapper.getEmpsByCondtionIf(employee);
for(Employee emp:emps) {
System.out.println(emp);
}
//查詢的時候如果某些條件沒帶可能sql拼裝會有問題
//1、給where后面加上1=1，以后的條件都and xxx.
//2、mybatis使用where標簽來將所有的查詢條件包括在內。
//mybatis就會將where標簽中拼裝的sql，多出來的and或者or去掉
//where只會去掉第一個多出來的and或者or。
//測試Trim
List<Employee> emps2 = mapper.getEmpsByCondtionTrim(employee);
for(Employee emp:emps2) {
System.out.println(emp);
}
} finally {
// : handle finally clause
openSession.close();
}
}
2).set
①.使用set更新
public void updateEmp(Employee employee);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<update id="updateEmp">
<!-- set:更新拼串 -->
<!-- set標簽的使用 -->
update tbl_employee
<set>
<if test="lastName!=null">
last_name=#{lastName},
</if>
<if test="email!=null">
email=#{email},
</if>
<if test="gender!=null">
gender=#{gender}
</if>
</set>
where id=#{id}
</update>
</mapper>
//調試set標簽 Employee employee = new Employee(1, "Adminn",null, null); mapper.updateEmp(employee); openSession.commit();
②.使用trim拼串更新
public void updateEmp(Employee employee);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- public void updateEmp(Employee employee) -->
<update id="updateEmp">
<!-- Trim：更新拼串 -->
update tbl_employee
<trim prefix="set" suffixOverrides=",">
<if test="lastName!=null">
last_name=#{lastName},
</if>
<if test="email!=null">
email=#{email},
</if>
<if test="gender!=null">
gender=#{gender}
</if>
</trim>
where id=#{id}
</update>
</mapper>
//調試set標簽 Employee employee = new Employee(1, "Adminn",null, null); mapper.updateEmp(employee); openSession.commit();
4.foreach
動態 SQL 的另外一個常用的必要操作是需要對一個集合進行遍歷，通常是在構建 IN 條件語句的時候.
當迭代列表、集合等可迭代對象或者數組時;index是當前迭代的次數，item的值是本次迭代獲取的元素.
當使用字典（或者Map.Entry對象的集合）時,index是鍵，item是值.
1).MySQL
(1).遍歷記錄
//查詢員工id'在給定集合中的
public List<Employee> getEmpsByConditionForeach(@Param("ids")List<Integer> ids);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- public List<Employee> getEmpsByConditionForeach(List<Integer> ids) -->
<select id="getEmpsByConditionForeach" resultType="com.atguigu.mybatis.bean.Employee">
<!-- collection:指定要遍歷的集合;list類型的參數會特殊處理封裝在map中,map的key就是list -->
<!-- item:當前遍歷出的元素賦值給指定的變量 -->
<!-- separator:每個元素之間的分隔符 -->
<!-- open：遍歷出所有結果拼接一個開始的字符 -->
<!-- close:遍歷出所有結果拼接一個結束的字符 -->
<!-- index:索引;遍歷list的時候是index就是索引,item就是當前值;遍歷map的時候index表示的就是map的key,item就是map的值 -->
<!-- #{變量名}:能取出變量的值也就是當前遍歷出的元素 -->
select * from tbl_employee
<foreach collection="ids" item="item_id" separator="," open="where id in(" close=")">
#{item_id}
</foreach>
</select>
</mapper>
//測試foreach
List<Employee> list = mapper.getEmpsByConditionForeach(Arrays.asList(1,2,3,4));
for(Employee emp : list) {
System.out.println(emp);
}
(2).批量保存記錄1
public void addEmps(@Param("emps")List<Employee> emps);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- 批量保存數據 -->
<!-- MySQL下批量保存:可以foreach遍歷 mysql支持values(),(),()語法 -->
<!-- public void addEmps(@Param("emps")List<Employee> emps) -->
<!-- insert 方式一 -->
<!-- 推薦使用inert 方式一 -->
<insert id="addEmps">
insert into tbl_employee(last_name,email,gender,d_id)
values
<foreach collection="emps" item="emp" separator=",">
(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
</foreach>
</insert>
</mapper>
List<Employee> emps = new ArrayList<>(); emps.add(new Employee(null, "smith", "smith@atguigu.com", "1",new Department(1))); emps.add(new Employee(null, "allen", "allen@atguigu.com", "0",new Department(1))); mapper.addEmps(emps); openSession.commit();
(3).批量保存記錄2
public void addEmps(@Param("emps")List<Employee> emps);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- insert 方式二 -->
<!-- public void addEmps(@Param("emps")List<Employee> emps) -->
<!-- 這種方式需要數據庫連接屬性allowMultiQueries=true；
這種分號分隔多個sql可以用於其他的批量操作（刪除，修改） -->
<insert id="addEmps">
<foreach collection="emps" item="emp" separator=";">
insert into tbl_employee(last_name,email,gender,d_id)
values(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
</foreach>
</insert>
</mapper>
List<Employee> emps = new ArrayList<>(); emps.add(new Employee(null, "smith", "smith@atguigu.com", "1",new Department(1))); emps.add(new Employee(null, "allen", "allen@atguigu.com", "0",new Department(1))); mapper.addEmps(emps); openSession.commit();
2).Oracle
(1).批量保存1
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<insert id="addEmps" databaseId="oracle">
<!-- oracle第一種批量方式 -->
<!-- <foreach collection="emps" item="emp" open="begin" close="end;">
insert into employees(employee_id,last_name,email)
values(employees_seq.nextval,#{emp.lastName},#{emp.email});
</foreach>
</insert>
</mapper>
(2).批量保存2
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<insert id="addEmps" databaseId="oracle">
<!-- oracle第二種批量方式 -->
insert into employees(
<!-- 引用外部定義的sql -->
<include refid="insertColumn">
<property name="testColomn" value="abc"/>
</include>
)
<foreach collection="emps" item="emp" separator="union"
open="select employees_seq.nextval,lastName,email from("
close=")">
select #{emp.lastName} lastName,#{emp.email} email from dual
</foreach>
</insert>
</mapper>
5.bind
bind 元素可以從 OGNL 表達式中創建一個變量並將其綁定到上下文.
1).bind
若在 mybatis 配置文件中配置了 databaseIdProvider , 則可以使用 “_databaseId”變量，這樣就可以根據不同的數據庫廠商構建特定的語句.
public List<Employee> getEmpsTestInnerParameter(Employee employee);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- public List<Employee> getEmpsTestInnerParameter(Employee employee) -->
<!-- mybatis默認還有兩個內置參數:_parameter|_databaseId -->
<!-- _parameter:代表整個參數;單個參數:_parameter就是這個參數;多個參數:參數會被封裝為一個map,_parameter就是代表這個map -->
<!-- _databaseId:如果配置了databaseIdProvider標簽;_databaseId就是代表當前數據庫的別名 -->
<select id="getEmpsTestInnerParameter" resultType="com.atguigu.mybatis.bean.Employee">
<!-- bind：可以將OGNL表達式的值綁定到一個變量中，方便后來引用這個變量的值 -->
<if test="_databaseId=='mysql'">
select * from tbl_employee
<if test="_parameter!=null">
where last_name like #{lastName}
</if>
</if>
<if test="_databaseId=='oracle'">
select * from employees
<if test="_parameter!=null">
where last_name like #{_parameter.lastName}
</if>
</if>
</select>
</mapper>
@Test
public void testInnerParam() throws IOException{
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try{
EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
Employee employee2 = new Employee();
employee2.setLastName("%e%");
List<Employee> list = mapper.getEmpsTestInnerParameter(employee2);
for (Employee employee : list) {
System.out.println(employee);
}
}finally{
openSession.close();
}
}
2).SQL片段
public void addEmps(@Param("emps")List<Employee> emps);
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
<!-- insert 方式三 -->
<insert id="addEmps">
insert into tbl_employee(
<include refid="insertColumn"></include>
)
values
<foreach collection="emps" item="emp" separator=",">
(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
</foreach>
</insert>
<!-- 抽取可重用的sql片段;方便后面引用 -->
<!-- 1、sql抽取:經常將要查詢的列名,或者插入用的列名抽取出來方便引用 -->
<!-- 2、include來引用已經抽取的sql -->
<!-- 3、include還可以自定義一些property，sql標簽內部就能使用自定義的屬性 -->
<!-- include-property：取值的正確方式${prop} #{不能使用這種方式} -->
<sql id="insertColumn">
<if test="_databaseId=='oracle'">
employee_id,last_name,email
</if>
<if test="_databaseId=='mysql'">
last_name,email,gender,d_id
</if>
</sql>
</mapper>
@Test
public void testBatchSave() throws IOException {
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try {
EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
List<Employee> emps = new ArrayList<>();
emps.add(new Employee(null, "smith", "smith@atguigu.com", "1",new Department(1)));
emps.add(new Employee(null, "allen", "allen@atguigu.com", "0",new Department(1)));
mapper.addEmps(emps);
openSession.commit();
}finally {
openSession.close();
}
}
6.OGNL
參考文檔：http://commons.apache.org/proper/commons-ognl/language-guide.html