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关于java:干掉mapperxmlMyBatis新特性动态SQL真香

作者：

jiezi

在

当咱们应用MyBatis的时候，须要在mapper.xml中书写大量的SQL语句。当咱们应用MyBatis Generator（MBG）作为代码生成器时，也会生成大量的mapper.xml文件。其实从MBG 1.3.6版本当前，MyBatis官网曾经举荐应用Dynamic SQL，应用这一新个性根本就不必写mapper.xml文件了，应用起来十分不便，举荐给大家！

SpringBoot实战电商我的项目mall（40k+star）地址：https://github.com/macrozheng/mall

Dynamic SQL简介

在咱们应用Spring的时候，有XML和Java两种配置形式。在应用SpringBoot时，曾经举荐应用Java配置，根本不必xml配置了。应用Dynamic SQL就好比是应用Java的形式来操作MyBatis。Dynamic SQL是用于生成动静SQL语句的框架，提倡应用Java API的形式来实现SQL操作，反对简单查问和多表查问。

Dynamic SQL具备如下个性：

  • 类型平安：能够确保参数类型和数据库字段类型相匹配；
  • 富裕表现力：语句的构建形式能够分明地传播其含意；
  • 应用灵便：能够应用and，or和nested条件的任意组合来构建where子句；
  • 扩展性强：能够同时为MyBatis3, Spring JDBC和纯JDBC框架生成SQL语句；
  • 轻量级：只需增加一个小的依赖项，没有传递依赖。

开始应用

首先咱们通过一个入门示例将Dynamic SQL用起来，该示例会蕴含根底的CRUD操作。对MBG应用不理解的敌人能够先看下之前的文章《解放双手！MyBatis官网代码生成工具给力！》

集成Dynamic SQL

  • 在pom.xml中增加如下依赖，比照之前应用MBG，仅仅多增加了MyBatis的动静SQL依赖；
<dependencies>
    <!--SpringBoot整合MyBatis-->
    <dependency>
        <groupId>org.mybatis.spring.boot</groupId>
        <artifactId>mybatis-spring-boot-starter</artifactId>
        <version>2.1.3</version>
    </dependency>
    <!--MyBatis分页插件-->
    <dependency>
        <groupId>com.github.pagehelper</groupId>
        <artifactId>pagehelper-spring-boot-starter</artifactId>
        <version>1.3.0</version>
    </dependency>
    <!--集成druid连接池-->
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>druid-spring-boot-starter</artifactId>
        <version>1.1.10</version>
    </dependency>
    <!-- MyBatis 生成器 -->
    <dependency>
        <groupId>org.mybatis.generator</groupId>
        <artifactId>mybatis-generator-core</artifactId>
        <version>1.4.0</version>
    </dependency>
    <!-- MyBatis 动静SQL反对 -->
    <dependency>
        <groupId>org.mybatis.dynamic-sql</groupId>
        <artifactId>mybatis-dynamic-sql</artifactId>
        <version>1.2.1</version>
    </dependency>
    <!--Mysql数据库驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.15</version>
    </dependency>
</dependencies>
  • 在application.yml中对数据源和MyBatis的mapper.xml文件门路进行配置，只需配置自定义mapper.xml门路即可；
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mall?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
    username: root
    password: root

mybatis:
  mapper-locations:
    - classpath:dao/*.xml
  • 增加Java配置，用于扫描Mapper接口门路，MBG生成的放在mapper包下，自定义的放在dao包下。
/**
 * MyBatis配置类
 * Created by macro on 2019/4/8.
 */
@Configuration
@MapperScan({"com.macro.mall.tiny.mbg.mapper","com.macro.mall.tiny.dao"})
public class MyBatisConfig {
}

应用代码生成器

  • 在应用MBG生成代码前，咱们还须要对其进行一些配置，首先在generator.properties文件中配置好数据库连贯信息；
jdbc.driverClass=com.mysql.cj.jdbc.Driver
jdbc.connectionURL=jdbc:mysql://localhost:3306/mall?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
jdbc.userId=root
jdbc.password=root
  • 而后在generatorConfig.xml文件中对MBG进行配置，配置属性阐明间接参考正文即可；
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">

<generatorConfiguration>
    <properties resource="generator.properties"/>
    <context id="MySqlContext" targetRuntime="MyBatis3DynamicSQL">
        <property name="beginningDelimiter" value="`"/>
        <property name="endingDelimiter" value="`"/>
        <property name="javaFileEncoding" value="UTF-8"/>
        <!-- 为模型生成序列化办法-->
        <plugin type="org.mybatis.generator.plugins.SerializablePlugin"/>
        <!-- 为生成的Java模型创立一个toString办法 -->
        <plugin type="org.mybatis.generator.plugins.ToStringPlugin"/>
        <!--能够自定义生成model的代码正文-->
        <commentGenerator type="com.macro.mall.tiny.mbg.CommentGenerator">
            <!-- 是否去除主动生成的正文 true：是 ： false:否 -->
            <property name="suppressAllComments" value="true"/>
            <property name="suppressDate" value="true"/>
            <property name="addRemarkComments" value="true"/>
        </commentGenerator>
        <!--配置数据库连贯-->
        <jdbcConnection driverClass="${jdbc.driverClass}"
                        connectionURL="${jdbc.connectionURL}"
                        userId="${jdbc.userId}"
                        password="${jdbc.password}">
            <!--解决mysql驱动降级到8.0后不生成指定数据库代码的问题-->
            <property name="nullCatalogMeansCurrent" value="true" />
        </jdbcConnection>
        <!--指定生成model的门路-->
        <javaModelGenerator targetPackage="com.macro.mall.tiny.mbg.model" targetProject="mall-tiny-dynamic-sql\src\main\java"/>
        <!--指定生成mapper接口的的门路-->
        <javaClientGenerator type="XMLMAPPER" targetPackage="com.macro.mall.tiny.mbg.mapper"
                             targetProject="mall-tiny-dynamic-sql\src\main\java"/>
        <!--生成全副表tableName设为%-->
        <table tableName="ums_admin">
            <generatedKey column="id" sqlStatement="MySql" identity="true"/>
        </table>
        <table tableName="ums_role">
            <generatedKey column="id" sqlStatement="MySql" identity="true"/>
        </table>
        <table tableName="ums_admin_role_relation">
            <generatedKey column="id" sqlStatement="MySql" identity="true"/>
        </table>
    </context>
</generatorConfiguration>
  • 与之前应用MBG有所不同，targetRuntime须要改为MyBatis3DynamicSql，用于配置生成mapper.xml门路的sqlMapGenerator标签也不须要配置了；
  • 之前应用MBG时自定义了实体类注解的生成，写了个类CommentGenerator继承DefaultCommentGenerator，在addFieldComment办法中将Swagger注解写入到了实体类的属性上；
/**
 * 自定义正文生成器
 * Created by macro on 2018/4/26.
 */
public class CommentGenerator extends DefaultCommentGenerator {
    /**
     * 给字段增加正文
     */
    @Override
    public void addFieldComment(Field field, IntrospectedTable introspectedTable,
                                IntrospectedColumn introspectedColumn) {
        String remarks = introspectedColumn.getRemarks();
        //依据参数和备注信息判断是否增加备注信息
        if(addRemarkComments&&StringUtility.stringHasValue(remarks)){
            //数据库中特殊字符须要本义
            if(remarks.contains("\"")){
                remarks = remarks.replace("\"","'");
            }
            //给model的字段增加swagger注解
            field.addJavaDocLine("@ApiModelProperty(value = \""+remarks+"\")");
        }
    }
}
  • 在应用Dynamic SQL的时候，这种办法曾经无用，须要在addFieldAnnotation中将Swagger注解写入到了实体类的属性上；
/**
 * 自定义正文生成器
 * Created by macro on 2018/4/26.
 */
public class CommentGenerator extends DefaultCommentGenerator {

    @Override
    public void addFieldAnnotation(Field field, IntrospectedTable introspectedTable, IntrospectedColumn introspectedColumn, Set<FullyQualifiedJavaType> imports) {
        if (!addRemarkComments || CollUtil.isEmpty(imports)) return;
        long count = imports.stream()
                .filter(item -> API_MODEL_PROPERTY_FULL_CLASS_NAME.equals(item.getFullyQualifiedName()))
                .count();
        if (count <= 0L) {
            return;
        }
        String remarks = introspectedColumn.getRemarks();
        //依据参数和备注信息判断是否增加备注信息
        if (StringUtility.stringHasValue(remarks)) {
            //数据库中特殊字符须要本义
            if (remarks.contains("\"")) {
                remarks = remarks.replace("\"", "'");
            }
            //给model的字段增加swagger注解
            field.addJavaDocLine("@ApiModelProperty(value = \"" + remarks + "\")");
        }
    }
}
  • 所有准备就绪，执行Generator类的main办法，生成代码构造信息如下，能够发现曾经不再生成mapper.xml文件和Example类，取而代之的是生成了DynamicSqlSupport类。

实现根本的CRUD操作

这里应用的是mall-tiny我的项目中权限治理性能相干表，具体能够参考《还在从零开始搭建我的项目？手撸了款疾速开发脚手架！》。

  • 查看下MBG生成的Mapper接口，比之前应用MBG时减少了很多办法，并且有了一些默认的办法实现，可见之前在mapper.xml中的实现都曾经转移到Mapper接口中去了，单表CRUD间接调用对应办法即可；
@Mapper
public interface UmsAdminMapper {
    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    BasicColumn[] selectList = BasicColumn.columnList(id, username, password, icon, email, nickName, note, createTime, loginTime, status);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    @SelectProvider(type=SqlProviderAdapter.class, method="select")
    long count(SelectStatementProvider selectStatement);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    @DeleteProvider(type=SqlProviderAdapter.class, method="delete")
    int delete(DeleteStatementProvider deleteStatement);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    @InsertProvider(type=SqlProviderAdapter.class, method="insert")
    @SelectKey(statement="SELECT LAST_INSERT_ID()", keyProperty="record.id", before=false, resultType=Long.class)
    int insert(InsertStatementProvider<UmsAdmin> insertStatement);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    @SelectProvider(type=SqlProviderAdapter.class, method="select")
    @ResultMap("UmsAdminResult")
    Optional<UmsAdmin> selectOne(SelectStatementProvider selectStatement);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    @SelectProvider(type=SqlProviderAdapter.class, method="select")
    @Results(id="UmsAdminResult", value = {
        @Result(column="id", property="id", jdbcType=JdbcType.BIGINT, id=true),
        @Result(column="username", property="username", jdbcType=JdbcType.VARCHAR),
        @Result(column="password", property="password", jdbcType=JdbcType.VARCHAR),
        @Result(column="icon", property="icon", jdbcType=JdbcType.VARCHAR),
        @Result(column="email", property="email", jdbcType=JdbcType.VARCHAR),
        @Result(column="nick_name", property="nickName", jdbcType=JdbcType.VARCHAR),
        @Result(column="note", property="note", jdbcType=JdbcType.VARCHAR),
        @Result(column="create_time", property="createTime", jdbcType=JdbcType.TIMESTAMP),
        @Result(column="login_time", property="loginTime", jdbcType=JdbcType.TIMESTAMP),
        @Result(column="status", property="status", jdbcType=JdbcType.INTEGER)
    })
    List<UmsAdmin> selectMany(SelectStatementProvider selectStatement);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    @UpdateProvider(type=SqlProviderAdapter.class, method="update")
    int update(UpdateStatementProvider updateStatement);

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default long count(CountDSLCompleter completer) {
        return MyBatis3Utils.countFrom(this::count, umsAdmin, completer);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int delete(DeleteDSLCompleter completer) {
        return MyBatis3Utils.deleteFrom(this::delete, umsAdmin, completer);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int deleteByPrimaryKey(Long id_) {
        return delete(c -> 
            c.where(id, isEqualTo(id_))
        );
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int insert(UmsAdmin record) {
        return MyBatis3Utils.insert(this::insert, record, umsAdmin, c ->
            c.map(username).toProperty("username")
            .map(password).toProperty("password")
            .map(icon).toProperty("icon")
            .map(email).toProperty("email")
            .map(nickName).toProperty("nickName")
            .map(note).toProperty("note")
            .map(createTime).toProperty("createTime")
            .map(loginTime).toProperty("loginTime")
            .map(status).toProperty("status")
        );
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int insertSelective(UmsAdmin record) {
        return MyBatis3Utils.insert(this::insert, record, umsAdmin, c ->
            c.map(username).toPropertyWhenPresent("username", record::getUsername)
            .map(password).toPropertyWhenPresent("password", record::getPassword)
            .map(icon).toPropertyWhenPresent("icon", record::getIcon)
            .map(email).toPropertyWhenPresent("email", record::getEmail)
            .map(nickName).toPropertyWhenPresent("nickName", record::getNickName)
            .map(note).toPropertyWhenPresent("note", record::getNote)
            .map(createTime).toPropertyWhenPresent("createTime", record::getCreateTime)
            .map(loginTime).toPropertyWhenPresent("loginTime", record::getLoginTime)
            .map(status).toPropertyWhenPresent("status", record::getStatus)
        );
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default Optional<UmsAdmin> selectOne(SelectDSLCompleter completer) {
        return MyBatis3Utils.selectOne(this::selectOne, selectList, umsAdmin, completer);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default List<UmsAdmin> select(SelectDSLCompleter completer) {
        return MyBatis3Utils.selectList(this::selectMany, selectList, umsAdmin, completer);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default List<UmsAdmin> selectDistinct(SelectDSLCompleter completer) {
        return MyBatis3Utils.selectDistinct(this::selectMany, selectList, umsAdmin, completer);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default Optional<UmsAdmin> selectByPrimaryKey(Long id_) {
        return selectOne(c ->
            c.where(id, isEqualTo(id_))
        );
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int update(UpdateDSLCompleter completer) {
        return MyBatis3Utils.update(this::update, umsAdmin, completer);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    static UpdateDSL<UpdateModel> updateAllColumns(UmsAdmin record, UpdateDSL<UpdateModel> dsl) {
        return dsl.set(username).equalTo(record::getUsername)
                .set(password).equalTo(record::getPassword)
                .set(icon).equalTo(record::getIcon)
                .set(email).equalTo(record::getEmail)
                .set(nickName).equalTo(record::getNickName)
                .set(note).equalTo(record::getNote)
                .set(createTime).equalTo(record::getCreateTime)
                .set(loginTime).equalTo(record::getLoginTime)
                .set(status).equalTo(record::getStatus);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    static UpdateDSL<UpdateModel> updateSelectiveColumns(UmsAdmin record, UpdateDSL<UpdateModel> dsl) {
        return dsl.set(username).equalToWhenPresent(record::getUsername)
                .set(password).equalToWhenPresent(record::getPassword)
                .set(icon).equalToWhenPresent(record::getIcon)
                .set(email).equalToWhenPresent(record::getEmail)
                .set(nickName).equalToWhenPresent(record::getNickName)
                .set(note).equalToWhenPresent(record::getNote)
                .set(createTime).equalToWhenPresent(record::getCreateTime)
                .set(loginTime).equalToWhenPresent(record::getLoginTime)
                .set(status).equalToWhenPresent(record::getStatus);
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int updateByPrimaryKey(UmsAdmin record) {
        return update(c ->
            c.set(username).equalTo(record::getUsername)
            .set(password).equalTo(record::getPassword)
            .set(icon).equalTo(record::getIcon)
            .set(email).equalTo(record::getEmail)
            .set(nickName).equalTo(record::getNickName)
            .set(note).equalTo(record::getNote)
            .set(createTime).equalTo(record::getCreateTime)
            .set(loginTime).equalTo(record::getLoginTime)
            .set(status).equalTo(record::getStatus)
            .where(id, isEqualTo(record::getId))
        );
    }

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    default int updateByPrimaryKeySelective(UmsAdmin record) {
        return update(c ->
            c.set(username).equalToWhenPresent(record::getUsername)
            .set(password).equalToWhenPresent(record::getPassword)
            .set(icon).equalToWhenPresent(record::getIcon)
            .set(email).equalToWhenPresent(record::getEmail)
            .set(nickName).equalToWhenPresent(record::getNickName)
            .set(note).equalToWhenPresent(record::getNote)
            .set(createTime).equalToWhenPresent(record::getCreateTime)
            .set(loginTime).equalToWhenPresent(record::getLoginTime)
            .set(status).equalToWhenPresent(record::getStatus)
            .where(id, isEqualTo(record::getId))
        );
    }
}
  • 生成代码中有一些DynamicSqlSupport类，比方UmsAdminDynamicSqlSupport，次要是把数据库表和字段形象成了SqlTable和SqlColumn对象，预计是为了避免咱们硬编码；
public final class UmsAdminDynamicSqlSupport {
    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    public static final UmsAdmin umsAdmin = new UmsAdmin();

    public static final SqlColumn<Long> id = umsAdmin.id;

    public static final SqlColumn<String> username = umsAdmin.username;

    public static final SqlColumn<String> password = umsAdmin.password;

    public static final SqlColumn<String> icon = umsAdmin.icon;

    public static final SqlColumn<String> email = umsAdmin.email;

    public static final SqlColumn<String> nickName = umsAdmin.nickName;

    public static final SqlColumn<String> note = umsAdmin.note;

    public static final SqlColumn<Date> createTime = umsAdmin.createTime;

    public static final SqlColumn<Date> loginTime = umsAdmin.loginTime;

    public static final SqlColumn<Integer> status = umsAdmin.status;

    @Generated("org.mybatis.generator.api.MyBatisGenerator")
    public static final class UmsAdmin extends SqlTable {
        public final SqlColumn<Long> id = column("id", JDBCType.BIGINT);

        public final SqlColumn<String> username = column("username", JDBCType.VARCHAR);

        public final SqlColumn<String> password = column("password", JDBCType.VARCHAR);

        public final SqlColumn<String> icon = column("icon", JDBCType.VARCHAR);

        public final SqlColumn<String> email = column("email", JDBCType.VARCHAR);

        public final SqlColumn<String> nickName = column("nick_name", JDBCType.VARCHAR);

        public final SqlColumn<String> note = column("note", JDBCType.VARCHAR);

        public final SqlColumn<Date> createTime = column("create_time", JDBCType.TIMESTAMP);

        public final SqlColumn<Date> loginTime = column("login_time", JDBCType.TIMESTAMP);

        public final SqlColumn<Integer> status = column("status", JDBCType.INTEGER);

        public UmsAdmin() {
            super("ums_admin");
        }
    }
}
  • 利用好MBG生成的代码即可实现单表的CRUD操作了，比方上面最常见的操作。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Autowired
    private UmsAdminMapper adminMapper;

    @Override
    public void create(UmsAdmin entity) {
        adminMapper.insert(entity);
    }

    @Override
    public void update(UmsAdmin entity) {
        adminMapper.updateByPrimaryKeySelective(entity);
    }

    @Override
    public void delete(Long id) {
        adminMapper.deleteByPrimaryKey(id);
    }

    @Override
    public UmsAdmin select(Long id) {
        Optional<UmsAdmin> optionalEntity = adminMapper.selectByPrimaryKey(id);
        return optionalEntity.orElse(null);
    }

    @Override
    public List<UmsAdmin> listAll(Integer pageNum, Integer pageSize) {
        PageHelper.startPage(pageNum, pageSize);
        return adminMapper.select(SelectDSLCompleter.allRows());
    }
}

进阶应用

想要用好Dynamic SQL，下面的根底操作是不够的，还须要一些进阶的应用技巧。

SqlBuilder

SqlBuilder是一个十分有用的类，应用它能够灵便地构建SQL语句的条件，一些罕用的条件构建办法如下。

条件 例子 对应SQL
Between where(foo, isBetween(x).and(y)) where foo between ? and ?
Equals where(foo, isEqualTo(x)) where foo = ?
Greater Than where(foo, isGreaterThan(x)) where foo > ?
In where(foo, isIn(x, y)) where foo in (?,?)
Like where(foo, isLike(x)) where foo like ?
Not Equals where(foo, isNotEqualTo(x)) where foo <> ?
Null where(foo, isNull()) where foo is null
Present Equals where(foo, isEqualToWhenPresent(x)) where foo = ? (will render if x is non-null)

StatementProvider

回忆一下之前咱们在mapper.xml中定义select标签的形式，各个select标签相当于Statement。而这里的StatementProvider好比是Statement中参数和SQL语句的封装，不便以Java的形式创立Statement。

条件查问

应用SqlBuilder类构建StatementProvider，而后调用Mapper接口中的办法即可。

  • 这里以按用户名和状态查问后盾用户并按创立工夫降序排列为例，SQL实现如下；
SELECT
    id,
    username,
    PASSWORD,
    icon,
    email,
    nick_name,
    note,
    create_time,
    login_time,
STATUS 
FROM
    ums_admin 
WHERE
    ( username = 'macro' AND STATUS IN ( 0, 1 ) ) 
ORDER BY
    create_time DESC;
  • 应用Dynamic SQL对应的Java代码实现如下，应用SqlBuilder的select办法能够指定查问列，应用from办法能够指定查问表，应用where办法能够构建查问条件，应用orderBy办法能够指定排序。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Override
    public List<UmsAdmin> list(Integer pageNum, Integer pageSize, String username, List<Integer> statusList) {
        PageHelper.startPage(pageNum, pageSize);
        SelectStatementProvider selectStatement = SqlBuilder.select(UmsAdminMapper.selectList)
                .from(UmsAdminDynamicSqlSupport.umsAdmin)
                .where(UmsAdminDynamicSqlSupport.username, isEqualToWhenPresent(username))
                .and(UmsAdminDynamicSqlSupport.status, isIn(statusList))
                .orderBy(UmsAdminDynamicSqlSupport.createTime.descending())
                .build()
                .render(RenderingStrategies.MYBATIS3);
        return adminMapper.selectMany(selectStatement);
    }
}

Lambda条件查问

应用Lambda表达式实现单表条件查问更加简略，实现下面的条件查问，对应Java代码实现如下。

/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Override
    public List<UmsAdmin> lambdaList(Integer pageNum, Integer pageSize, String username, List<Integer> statusList) {
        PageHelper.startPage(pageNum, pageSize);
        List<UmsAdmin> list = adminMapper.select(c -> c.where(UmsAdminDynamicSqlSupport.username, isEqualToWhenPresent(username))
                .and(UmsAdminDynamicSqlSupport.status, isIn(statusList))
                .orderBy(UmsAdminDynamicSqlSupport.createTime.descending()));
        return list;
    }
}

子查问

之前应用MBG须要在mapper.xml中手写SQL能力实现子查问，应用Dynamic SQL能够间接在Java代码中实现。

  • 这里以按角色ID查问后盾用户为例，SQL实现如下；
SELECT
    * 
FROM
    ums_admin 
WHERE
    id IN ( SELECT admin_id FROM ums_admin_role_relation WHERE role_id = 1 )
  • 应用Dynamic SQL对应的Java代码实现如下，能够发现SqlBuilder的条件构造方法isIn中还能够嵌套SqlBuilder的查问。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Override
    public List<UmsAdmin> subList(Long roleId) {
        SelectStatementProvider selectStatement = SqlBuilder.select(UmsAdminMapper.selectList)
                .from(UmsAdminDynamicSqlSupport.umsAdmin)
                .where(UmsAdminDynamicSqlSupport.id, isIn(SqlBuilder.select(UmsAdminRoleRelationDynamicSqlSupport.adminId)
                        .from(UmsAdminRoleRelationDynamicSqlSupport.umsAdminRoleRelation)
                        .where(UmsAdminRoleRelationDynamicSqlSupport.roleId, isEqualTo(roleId))))
                .build()
                .render(RenderingStrategies.MYBATIS3);
        return adminMapper.selectMany(selectStatement);
    }
}

Group和Join查问

波及到多表查问，之前应用MBG的时候根本只能在mapper.xml中手写SQL实现，应用Dynamic SQL能够反对多表查问。

  • 这里以按角色统计后盾用户数量为例，SQL实现如下；
SELECT
    ur.id AS roleId,
    ur.NAME AS roleName,
    count( ua.id ) AS count 
FROM
    ums_role ur
    LEFT JOIN ums_admin_role_relation uarr ON ur.id = uarr.role_id
    LEFT JOIN ums_admin ua ON uarr.admin_id = ua.id 
GROUP BY
    ur.id;
  • 先在Dao中增加一个groupList办法，而后应用@Results注解定义好resultMap；
/**
 * Created by macro on 2020/12/9.
 */
public interface UmsAdminDao {
    @SelectProvider(type = SqlProviderAdapter.class, method = "select")
    @Results(id = "RoleStatResult", value = {
            @Result(column = "roleId", property = "roleId", jdbcType = JdbcType.BIGINT, id = true),
            @Result(column = "roleName", property = "roleName", jdbcType = JdbcType.VARCHAR),
            @Result(column = "count", property = "count", jdbcType = JdbcType.INTEGER)
    })
    List<RoleStatDto> groupList(SelectStatementProvider selectStatement);
}
  • 而后在Service中调用groupList办法传入StatementProvider即可，对应的Java代码实现如下。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Override
    public List<RoleStatDto> groupList() {
        SelectStatementProvider selectStatement = SqlBuilder.select(UmsRoleDynamicSqlSupport.id.as("roleId"), UmsRoleDynamicSqlSupport.name.as("roleName"), count(UmsAdminDynamicSqlSupport.id).as("count"))
                .from(UmsRoleDynamicSqlSupport.umsRole)
                .leftJoin(UmsAdminRoleRelationDynamicSqlSupport.umsAdminRoleRelation)
                .on(UmsRoleDynamicSqlSupport.id, equalTo(UmsAdminRoleRelationDynamicSqlSupport.roleId))
                .leftJoin(UmsAdminDynamicSqlSupport.umsAdmin)
                .on(UmsAdminRoleRelationDynamicSqlSupport.adminId, equalTo(UmsAdminDynamicSqlSupport.id))
                .groupBy(UmsRoleDynamicSqlSupport.id)
                .build()
                .render(RenderingStrategies.MYBATIS3);
        return adminDao.groupList(selectStatement);
    }
}

条件删除

应用Dynamic SQL实现条件删除，间接调用Mapper接口中生成好的delete办法即可。

  • 这里以按用户名删除后盾用户为例，SQL实现如下；
DELETE 
FROM
    ums_admin 
WHERE
    username = 'andy';
  • 应用Dynamic SQL对应Java中的实现如下。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Override
    public void deleteByUsername(String username) {
        DeleteStatementProvider deleteStatement = SqlBuilder.deleteFrom(UmsAdminDynamicSqlSupport.umsAdmin)
                .where(UmsAdminDynamicSqlSupport.username, isEqualTo(username))
                .build()
                .render(RenderingStrategies.MYBATIS3);
        adminMapper.delete(deleteStatement);
    }
}

条件批改

应用Dynamic SQL实现条件批改，间接调用Mapper接口中生成好的update办法即可。

  • 这里以按指定ID批改后盾用户的状态为例，SQL实现如下；
UPDATE ums_admin 
SET STATUS = 1 
WHERE
    id IN ( 1, 2 );
  • 应用Dynamic SQL对应Java中的实现如下。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {
    @Override
    public void updateByIds(List<Long> ids, Integer status) {
        UpdateStatementProvider updateStatement = SqlBuilder.update(UmsAdminDynamicSqlSupport.umsAdmin)
                .set(UmsAdminDynamicSqlSupport.status).equalTo(status)
                .where(UmsAdminDynamicSqlSupport.id, isIn(ids))
                .build()
                .render(RenderingStrategies.MYBATIS3);
        adminMapper.update(updateStatement);
    }
}

一对多查问

应用Dynamic SQL也能够实现一对多查问，只是因为Java注解无奈实现循环援用，所以一对多的resultMap只能在mapper.xml来配置，这可能是惟一须要应用mapper.xml的中央。

  • 这里以按ID查问后盾用户信息（蕴含对应角色列表）为例，SQL实现如下；
SELECT
    ua.*,
    ur.id AS role_id,
    ur.NAME AS role_name,
    ur.description AS role_description,
    ur.create_time AS role_create_time,
    ur.STATUS AS role_status,
    ur.sort AS role_sort 
FROM
    ums_admin ua
    LEFT JOIN ums_admin_role_relation uarr ON ua.id = uarr.admin_id
    LEFT JOIN ums_role ur ON uarr.role_id = ur.id 
WHERE
    ua.id = 1
  • 而后在Dao接口中增加selectWithRoleList办法，这里应用@ResultMap注解援用mapper.xml中定义的resultMap；
/**
 * Created by macro on 2020/12/9.
 */
public interface UmsAdminDao {

    @SelectProvider(type = SqlProviderAdapter.class, method = "select")
    @ResultMap("AdminRoleResult")
    AdminRoleDto selectWithRoleList(SelectStatementProvider selectStatement);
}
  • 在mapper.xml中增加名称为AdminRoleResult的resultMap，这里有个小技巧，能够间接援用在Mapper接口中定义好的resultMap；
<resultMap id="AdminRoleResult" type="com.macro.mall.tiny.domain.AdminRoleDto"
           extends="com.macro.mall.tiny.mbg.mapper.UmsAdminMapper.UmsAdminResult">
    <collection property="roleList" resultMap="com.macro.mall.tiny.mbg.mapper.UmsRoleMapper.UmsRoleResult" columnPrefix="role_">
    </collection>
</resultMap>
  • 而后在Service实现类中调用即可，为了不便后果集映射给查问列取了别名。
/**
 * 后盾用户治理Service实现类
 * Created by macro on 2020/12/8.
 */
@Service
public class UmsAdminServiceImpl implements UmsAdminService {   
    @Override
    public AdminRoleDto selectWithRoleList(Long id) {
        List<BasicColumn> columnList = new ArrayList<>(CollUtil.toList(UmsAdminMapper.selectList));
        columnList.add(UmsRoleDynamicSqlSupport.id.as("role_id"));
        columnList.add(UmsRoleDynamicSqlSupport.name.as("role_name"));
        columnList.add(UmsRoleDynamicSqlSupport.description.as("role_description"));
        columnList.add(UmsRoleDynamicSqlSupport.createTime.as("role_create_time"));
        columnList.add(UmsRoleDynamicSqlSupport.status.as("role_status"));
        columnList.add(UmsRoleDynamicSqlSupport.sort.as("role_sort"));
        SelectStatementProvider selectStatement = SqlBuilder.select(columnList)
                .from(UmsAdminDynamicSqlSupport.umsAdmin)
                .leftJoin(UmsAdminRoleRelationDynamicSqlSupport.umsAdminRoleRelation)
                .on(UmsAdminDynamicSqlSupport.id, equalTo(UmsAdminRoleRelationDynamicSqlSupport.adminId))
                .leftJoin(UmsRoleDynamicSqlSupport.umsRole)
                .on(UmsAdminRoleRelationDynamicSqlSupport.roleId, equalTo(UmsRoleDynamicSqlSupport.id))
                .where(UmsAdminDynamicSqlSupport.id, isEqualTo(id))
                .build()
                .render(RenderingStrategies.MYBATIS3);
        return adminDao.selectWithRoleList(selectStatement);
    }
}

总结

当咱们应用MyBatis官网代码生成器MBG时，配置的targetRuntime决定了应用它的应用形式。Dynamic SQL更偏向于应用Java API来实现SQL操作，传统的形式更偏向于在mapper.xml中手写SQL来实现SQL操作。尽管MyBatis官网举荐应用Dynamic SQL，但抉择那种形式全看集体习惯了！

参考资料

官网文档：https://mybatis.org/mybatis-d…

我的项目源码地址

https://github.com/macrozheng…

本文 GitHub https://github.com/macrozheng/mall-learning 曾经收录，欢送大家Star！

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