1

src/main/java/com/fdkankan/agent/mapper/IContactUsMapper.java

@@ -4,6 +4,8 @@ import com.fdkankan.agent.entity.ContactUs;
 import com.baomidou.mybatisplus.core.mapper.BaseMapper;
 import org.apache.ibatis.annotations.Mapper;
 
+import java.util.List;
+
 /**
  * <p>
  *  Mapper 接口
@@ -15,4 +17,5 @@ import org.apache.ibatis.annotations.Mapper;
 @Mapper
 public interface IContactUsMapper extends BaseMapper<ContactUs> {
 
+    List<String> groupByCountry();
 }

src/main/java/com/fdkankan/agent/service/impl/ContactUsServiceImpl.java

@@ -66,10 +66,7 @@ public class ContactUsServiceImpl extends ServiceImpl<IContactUsMapper, ContactU
 
     @Override
     public List<String> getAllCountry() {
-        LambdaQueryWrapper<ContactUs> wrapper = new LambdaQueryWrapper<>();
-        wrapper.groupBy(ContactUs::getCountry);
-        List<ContactUs> list = this.list(wrapper);
-        return list.stream().map(ContactUs::getCountry).collect(Collectors.toList());
+        return this.getBaseMapper().groupByCountry();
     }
 
     @Override

src/main/resources/mapper/agent/ContactUsMapper.xml

@@ -2,4 +2,7 @@
 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="com.fdkankan.agent.mapper.IContactUsMapper">
 
+    <select id="groupByCountry" resultType="java.lang.String">
+        select country from t_contact_us group by country
+    </select>
 </mapper>