MybatisPlus BaseMapper 實現對數據庫增刪改查源碼

Posted on 2023-02-01 by WalkonNet

環境搭建

1、使用 h2 數據庫，方便測試，導入相關依賴

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web:2.7.1'
    implementation 'com.baomidou:mybatis-plus-boot-starter:3.5.3.1'
    implementation 'org.projectlombok:lombok:1.18.24'
    implementation 'com.h2database:h2:1.4.200'
}

2、springboot 配置文件

spring:
  datasource:
    driver-class-name: org.h2.Driver
    username: root
    password: test
  sql:
    init:
      schema-locations: classpath:db/schema-h2.sql
      data-locations: classpath:db/data-h2.sql

3、resources 目錄下新建 db 目錄，創建 sql 文件

schema-h2.sql

DROP TABLE IF EXISTS demo_user;

CREATE TABLE demo_user
(
    id int primary key,
    name varchar,
    age int,
    email varchar
);

data-h2.sql

DELETE
FROM demo_user;

INSERT INTO demo_user (id, name, age, email)
VALUES (1, 'Jone', 18, '[email protected]'),
       (2, 'Jack', 20, '[email protected]'),
       (3, 'Tom', 28, '[email protected]'),
       (4, 'Sandy', 21, '[email protected]'),
       (5, 'Billie', 24, '[email protected]');

4、編寫 mapper 文件

public interface UserMapper extends BaseMapper<User> {
}

5、啟動測試

@MapperScan("org.example.mapper")
@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(Main.class, args);
        UserMapper userMapper = context.getBean(UserMapper.class);
        System.out.println(userMapper.selectList(null));
    }
}

結果如下

[User(id=1, name=Jone, age=18, [email protected]), User(id=2, name=Jack, age=20, [email protected]), User(id=3, name=Tom, age=28, [email protected]), User(id=4, name=Sandy, age=21, [email protected]), User(id=5, name=Billie, age=24, [email protected])]

從 @MapperScan 入手

@MapperScan 註解的作用是掃描指定 mapper 接口所在的包，並生成接口的代理對象，註入到 ioc 容器中，接口定義如下

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
@Repeatable(MapperScans.class)
public @interface MapperScan {
}

可以看到 Import 瞭個 MapperScannerRegistrar，點進去看看這個類做瞭什麼

@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    AnnotationAttributes mapperScanAttrs = AnnotationAttributes
        .fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
    if (mapperScanAttrs != null) {
      // 註冊一個 beanDefinition
      registerBeanDefinitions(importingClassMetadata, mapperScanAttrs, registry,
          generateBaseBeanName(importingClassMetadata, 0));
    }
}

void registerBeanDefinitions(AnnotationMetadata annoMeta, AnnotationAttributes annoAttrs,
  BeanDefinitionRegistry registry, String beanName) {

    // 註冊MapperScannerConfigurer的BeanDefinition
    BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
    // ......
    registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
}

這個 importRegister 註冊瞭一個 MapperScannerConfigurer，這個類是個 BeanDefinitionRegistryPostProcessor，核心邏輯就是在這個類中，即掃描指定 mapper 接口所在的包，並生成接口的代理對象，註入到 ioc 容器中，查看該類的 postProcessBeanDefinitionRegistry() 方法

@Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    if (this.processPropertyPlaceHolders) {
      processPropertyPlaceHolders();
    }

    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    // 設置一些scanner參數
    scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
    // ......
    // 掃描mapper接口
    scanner.scan(
        StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }

進入父類 scan 方法，發現核心方法是子類的 doScan(), 來到 MapperScannerConfigurer.doScan()

@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
    // 拿到掃描到的 beanDefinition
    Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);

    if (beanDefinitions.isEmpty()) {
      LOGGER.warn(() -> "No MyBatis mapper was found in '" + Arrays.toString(basePackages)
          + "' package. Please check your configuration.");
    } else {
      // 處理 mapper beanDefinition
      processBeanDefinitions(beanDefinitions);
    }

    return beanDefinitions;
}

核心在 processBeanDefinitions(beanDefinitions) 中

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    AbstractBeanDefinition definition;
    BeanDefinitionRegistry registry = getRegistry();
    for (BeanDefinitionHolder holder : beanDefinitions) {
      definition = (AbstractBeanDefinition) holder.getBeanDefinition();

      // 設置該BeanDefinition的beanClass是 MapperFactoryBean
      definition.setBeanClass(this.mapperFactoryBeanClass);

      // ......

      // 設置該MapperFactoryBean 中的 sqlSessionTemplateBeanName
      if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
        definition.getPropertyValues().add("sqlSessionTemplate",
            new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
        explicitFactoryUsed = true;
      }

      // ......

    }
}

通過這一系列源碼，可以知道，@MapperScan 指定的包在 MapperScannerConfigurer 被掃描成 BeanDefinition, 並且修改瞭 BeanDefinition 的 beanClass 屬性為 MapperFactory，這樣 spring 實例化 UserMapper 單例 bean 時，會生成對應的 MapperFactory

看看這個 MapperFactory 是什麼鬼

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {

  @Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }
  
  public SqlSession getSqlSession() {
    return this.sqlSessionTemplate;
  }

}

這個類是個 FactoryBean，那麼它的 getObject() 方法就是調用 sqlSessionTemplate 的 getMapper() 方法獲取代理對象，關於這個 getMapper() 方法的解析，可以參考我之前寫的《Mybatis 通過接口實現 sql 執行原理解析》

到這裡，MapperFactory 生成的 bean 被放到瞭 ioc 容器中，結束瞭嗎？我們忽略瞭 MapperFactory 的父類 SqlSessionDaoSupport，下面一節來看看這個父類 SqlSessionDaoSupport 做瞭什麼

SqlSessionDaoSupport

這個類看名字是給 Dao 做支持的，Dao 指的就是那個 mapper 接口，做什麼支持？其實給就是給 BaseMapper 裡定義的方法生成對應的 Statemnet，註冊到 MybatisMapperRegistry 中，這樣調用 BaseMapper 方法時，代理類就會從 MybatisMapperRegistry 中找到 Statemnet，這樣可以取出 sql 執行瞭，來看源碼，其他都是抽象方法，隻有一個初始化方法

@Override
public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException {
    // 讓子類處理
    checkDaoConfig();

    // Let concrete implementations initialize themselves.
    try {
            initDao();
    }
    catch (Exception ex) {
            throw new BeanInitializationException("Initialization of DAO failed", ex);
    }
}

調用瞭抽象方法，子類實現瞭 checkDaoConfig()，來看下 MapperFactoryBean.checkDaoConfig()

protected void checkDaoConfig() {
    super.checkDaoConfig();
    Assert.notNull(this.mapperInterface, "Property 'mapperInterface' is required");
    Configuration configuration = this.getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
        try {
            // 解析這個 mapper 方法
            configuration.addMapper(this.mapperInterface);
        } catch (Exception var6) {
            this.logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", var6);
            throw new IllegalArgumentException(var6);
        } finally {
            ErrorContext.instance().reset();
        }
    }

}

看到 configuration.addMapper(this.mapperInterface) 方法，相信看過 mybatis 源碼的小夥伴們已經知道要幹什麼瞭吧。就是解析這個 mapper 類方法，找到對應的 sql，並封裝成 statemnet，下面看看這個 configuration.addMapper(this.mapperInterface) 的實現邏輯吧

MybatisConfiguration.addMapper()

因為是 MybatisPlus，所以源碼內部的 Configuration 類是 MybatisConfiguration，查看他的 addMapper() 方法源碼

@Override
public <T> void addMapper(Class<T> type) {
    mybatisMapperRegistry.addMapper(type);
}

再進入 mybatisMapperRegistry.addMapper(type) 源碼

@Override
public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) {
        if (hasMapper(type)) {
            // TODO 如果之前註入 直接返回
            return;
        }
        boolean loadCompleted = false;
        try {
            // TODO 註冊mapper類對應的代理工廠類，用於生成代理對象
            knownMappers.put(type, new MybatisMapperProxyFactory<>(type));
            MybatisMapperAnnotationBuilder parser = new MybatisMapperAnnotationBuilder(config, type);
            // 解析mapper類，生成 statement
            parser.parse();
            loadCompleted = true;
        } finally {
            if (!loadCompleted) {
                knownMappers.remove(type);
            }
        }
    }
}

進入 parse() 方法查看

@Override
public void parse() {
    String resource = type.toString();
    if (!configuration.isResourceLoaded(resource)) {
        // 解析mapper.xml
        loadXmlResource();
        configuration.addLoadedResource(resource);
        String mapperName = type.getName();
        assistant.setCurrentNamespace(mapperName);
        // 解析緩存
        parseCache();
        parseCacheRef();
        IgnoreStrategy ignoreStrategy = InterceptorIgnoreHelper.initSqlParserInfoCache(type);
        for (Method method : type.getMethods()) {
            if (!canHaveStatement(method)) {
                continue;
            }
            if (getAnnotationWrapper(method, false, Select.class, SelectProvider.class).isPresent()
                && method.getAnnotation(ResultMap.class) == null) {
                parseResultMap(method);
            }
            try {
                // TODO 加入 註解過濾緩存
                InterceptorIgnoreHelper.initSqlParserInfoCache(ignoreStrategy, mapperName, method);
                parseStatement(method);
            } catch (IncompleteElementException e) {
                // TODO 使用 MybatisMethodResolver 而不是 MethodResolver
                configuration.addIncompleteMethod(new MybatisMethodResolver(this, method));
            }
        }
        // TODO 註入 CURD 動態 SQL , 放在在最後, because 可能會有人會用註解重寫sql
        try {
            // https://github.com/baomidou/mybatis-plus/issues/3038
            if (GlobalConfigUtils.isSupperMapperChildren(configuration, type)) {
                parserInjector();
            }
        } catch (IncompleteElementException e) {
            configuration.addIncompleteMethod(new InjectorResolver(this));
        }
    }
    parsePendingMethods();
}

關註最後註釋，註入 CRUD 動態 SQL，其實就是給 BaseMapper 裡的方法創建對應的 Statement，查看內部邏輯：

void parserInjector() {
    // DefaultSqlInjector.inspectInject();
    GlobalConfigUtils.getSqlInjector(configuration).inspectInject(assistant, type);
}

這裡先獲取到默認的 Sql 註入器 DefaultSqlInjector，再調用其 inspectInject() 方法註入 sql

@Override
public void inspectInject(MapperBuilderAssistant builderAssistant, Class<?> mapperClass) {
    Class<?> modelClass = ReflectionKit.getSuperClassGenericType(mapperClass, Mapper.class, 0);
    if (modelClass != null) {
        String className = mapperClass.toString();
        Set<String> mapperRegistryCache = GlobalConfigUtils.getMapperRegistryCache(builderAssistant.getConfiguration());
        if (!mapperRegistryCache.contains(className)) {
            // 根據實體類，根據註解解析出表的信息
            TableInfo tableInfo = TableInfoHelper.initTableInfo(builderAssistant, modelClass);
            // 拿到所有的AbstractMethod實現類
            List<AbstractMethod> methodList = this.getMethodList(mapperClass, tableInfo);
            if (CollectionUtils.isNotEmpty(methodList)) {
                // 循環註入自定義方法
                methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo));
            } else {
                logger.debug(mapperClass.toString() + ", No effective injection method was found.");
            }
            mapperRegistryCache.add(className);
        }
    }
}

這裡面的 AbstractMethod 的實現類有很多，如下

可以說，BaseMapper 中每個方法都有一個對應的 AbstractMethod 實現類，以 selectList() 為例，可以找到 SelectList 類

在下面循環註入的地方：methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo)), 進入 AbstractMethod.inject() 方法

public void inject(MapperBuilderAssistant builderAssistant, Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
    this.configuration = builderAssistant.getConfiguration();
    this.builderAssistant = builderAssistant;
    this.languageDriver = configuration.getDefaultScriptingLanguageInstance();
    /* 註入自定義方法 */
    injectMappedStatement(mapperClass, modelClass, tableInfo);
}

子類實現瞭 injectMappedStatement 方法，還是以 SelectList 為例

@Override
public MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
    // selectList sql 模版
    SqlMethod sqlMethod = SqlMethod.SELECT_LIST;
    // 格式化sql
    String sql = String.format(sqlMethod.getSql(), sqlFirst(), sqlSelectColumns(tableInfo, true), tableInfo.getTableName(),
        sqlWhereEntityWrapper(true, tableInfo), sqlOrderBy(tableInfo), sqlComment());
    // 封裝成 sqlSource 
    SqlSource sqlSource = languageDriver.createSqlSource(configuration, sql, modelClass);
    // 註冊 mapperStatement
    return this.addSelectMappedStatementForTable(mapperClass, methodName, sqlSource, tableInfo);
}

其中 sqlSelectColumns(tableInfo, true) 方法是構造出 select 的所有列名，並加上動態sql標簽

<choose>
    <when test="ew != null and ew.sqlSelect != null">
    ${ew.sqlSelect}
    </when>
    <otherwise>id,name,age,email</otherwise>
</choose>

其中 sqlWhereEntityWrapper(true, tableInfo) 方法是構造出 where 後面的條件語句，並加上動態sql標簽

<if test="ew != null">
<where>
    <if test="ew.entity != null">
    <if test="ew.entity.id != null">id=#{ew.entity.id}</if>
    <if test="ew.entity['name'] != null"> AND name=#{ew.entity.name}</if>
    <if test="ew.entity['age'] != null"> AND age=#{ew.entity.age}</if>
    <if test="ew.entity['email'] != null"> AND email=#{ew.entity.email}</if>
    </if>
    <if test="ew.sqlSegment != null and ew.sqlSegment != '' and ew.nonEmptyOfWhere">
    <if test="ew.nonEmptyOfEntity and ew.nonEmptyOfNormal"> AND</if> ${ew.sqlSegment}
    </if>
</where>
<if test="ew.sqlSegment != null and ew.sqlSegment != '' and ew.emptyOfWhere">
 ${ew.sqlSegment}
</if>
</if>

最後 format 後的 sql 語句是

<script>
    <if test="ew != null and ew.sqlFirst != null">
        ${ew.sqlFirst}
        </if> SELECT <choose>
        <when test="ew != null and ew.sqlSelect != null">
        ${ew.sqlSelect}
        </when>
        <otherwise>id,name,age,email</otherwise>
        </choose> FROM demo_user 
        <if test="ew != null">
        <where>
        <if test="ew.entity != null">
        <if test="ew.entity.id != null">id=#{ew.entity.id}</if>
        <if test="ew.entity['name'] != null"> AND name=#{ew.entity.name}</if>
        <if test="ew.entity['age'] != null"> AND age=#{ew.entity.age}</if>
        <if test="ew.entity['email'] != null"> AND email=#{ew.entity.email}</if>
        </if>
        <if test="ew.sqlSegment != null and ew.sqlSegment != '' and ew.nonEmptyOfWhere">
        <if test="ew.nonEmptyOfEntity and ew.nonEmptyOfNormal"> AND</if> ${ew.sqlSegment}
        </if>
        </where>
        <if test="ew.sqlSegment != null and ew.sqlSegment != '' and ew.emptyOfWhere">
         ${ew.sqlSegment}
        </if>
        </if>  <if test="ew != null and ew.sqlComment != null">
        ${ew.sqlComment}
        </if>
</script>

最後是把 sql 封裝成瞭 SqlSource，並構造 MapperStatement 存入 configuration.mappedStatements 中，後面 mapper 調用 selectList 方法時，會從 mappedStatements 中找到對應的 statement，並取出 sql 語句執行，就能拿到數據瞭

小結

到此，MybatisPlus BaseMapper 實現對數據庫增刪改查源碼解析完畢，相信通過源碼的閱讀能對 mybatisPlus 有更深的瞭解

到此這篇關於MybatisPlus BaseMapper 實現對數據庫增刪改查源碼解析的文章就介紹到這瞭,更多相關MybatisPlus BaseMapper 數據庫增刪改查內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

MybatisPlus BaseMapper 實現對數據庫增刪改查源碼

目錄

環境搭建

從 @MapperScan 入手

SqlSessionDaoSupport

MybatisConfiguration.addMapper()

小結

推薦閱讀：

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近期文章

目錄

環境搭建

從 @MapperScan 入手

SqlSessionDaoSupport

MybatisConfiguration.addMapper()

小結

推薦閱讀：

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近期文章

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