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README
Apache-2.0

通用 Mapper 核心实现 Provider

核心中定义了对象和表之间映射关系数据的结构和获取方式,通过 SPI 支持部分自定义扩展。

核心中也定义了 Provider 中的实现中需要返回 namespace.methodName 类型的字符串(而不是SQL),通过中间缓存在 Caching 中获取真正的 SQL 信息。

当前项目没有直接提供可用的通用方法,方法在 mybatis-mapper/mapper( gitee | GitHub )中提供。

注解

核心提供了一套实体类的注解,简单示例如下:


@Entity.Table(value = "user")
public class User {
  @Entity.Column(id = true)
  private Long   id;
  @Entity.Column("name")
  private String userName;
  @Entity.Column
  private String sex;
  //省略其他
}

除了最基本的注解配置外,还有更多可配置的属性,下面是个复杂的例子:

//autoResultMap 自动生成 <resultMap> 结果映射,支持查询结果中的 typeHandler 等配置
@Entity.Table(value = "sys_user", remark = "系统用户", autoResultMap = true,
  props = {
    //deleteByExample方法中的Example条件不能为空,默认允许空,另外两个配置类似
    @Entity.Prop(name = "deleteByExample.allowEmpty", value = "false", type = Boolean.class),
    @Entity.Prop(name = "updateByExample.allowEmpty", value = "false", type = Boolean.class),
    @Entity.Prop(name = "updateByExampleSelective.allowEmpty", value = "false", type = Boolean.class)
  })
public class User {
  @Entity.Column(id = true, remark = "主键", updatable = false, insertable = false)
  private Long    id;
  @Entity.Column(value = "name", remark = "帐号")
  private String  name;
  @Entity.Column(value = "is_admin", remark = "是否为管理员", updatable = false)
  private boolean admin;
  @Entity.Column(remark = "顺序号", orderBy = "DESC")
  private Integer seq;
  @Entity.Column(numericScale = "4", remark = "积分(保留4位小数)")
  private Double  points;
  @Entity.Column(selectable = false, remark = "密码")
  private String  password;
  @Entity.Column(value = "when_created", remark = "创建时间", jdbcType = JdbcType.TIMESTAMP)
  private Date    whenCreated;
  @Entity.Column(remark = "介绍", typeHandler = StringTypeHandler.class)
  private String  info;
  //不是表字段
  private String  noEntityColumn;
  //省略其他
}

拼接 SQL 的方法

提供了 SqlScript 类用于拼接 XML 形式的 SQL,简单示例如下:

class DemoProvider {
  /**
   * 根据主键删除
   *
   * @param providerContext 上下文
   * @return cacheKey
   */
  public static String deleteByPrimaryKey(ProviderContext providerContext) {
    return SqlScript.caching(providerContext, entity -> "DELETE FROM " + entity.table()
      + " WHERE " + entity.idColumns().stream().map(EntityColumn::columnEqualsProperty).collect(Collectors.joining(" AND ")));
  }
}

SqlScript.caching 会缓存拼接 SQL 的 lambda 方法,并且返回方法的 id。

特别注意,这里返回的不是 sql,而且缓存 SQL 后的 key
key值形式如:io.mybatis.mapper.UserMapper.deleteByPrimaryKey

上面方法在执行时,最终拼接的 SQL 示例如下:


<script>
  DELETE FROM user WHERE id = #{id}
</script>

复杂一点的:

class DemoProvider {
  /**
   * 根据主键查询实体
   *
   * @param providerContext 上下文
   * @return cacheKey
   */
  public static String selectByPrimaryKey(ProviderContext providerContext) {
    return SqlScript.caching(providerContext, new SqlScript() {
      @Override
      public String getSql(EntityTable entity) {
        return "SELECT " + entity.baseColumnAsPropertyList()
          + " FROM " + entity.table()
          + where(() -> entity.idColumns().stream().map(EntityColumn::columnEqualsProperty).collect(Collectors.joining(" AND ")));
      }
    });
  }
}

上面方法在执行时,最终拼接的 SQL 示例如下:

<script>
  SELECT id,name AS userName,sex FROM user
  <where>
    id = #{id}
  </where>
</script>

更复杂的:

class DemoProvider {
  /**
   * 保存实体中不为空的字段
   *
   * @param providerContext 上下文
   * @return cacheKey
   */
  public static String insertSelective(ProviderContext providerContext) {
    return SqlScript.caching(providerContext, new SqlScript() {
      @Override
      public String getSql(EntityTable entity) {
        return "INSERT INTO " + entity.table()
          + trimSuffixOverrides("(", ")", ",", () ->
          entity.insertColumns().stream().map(column ->
            ifTest(column.notNullTest(), () -> column.column() + ",")
          ).collect(Collectors.joining(LF)))
          + trimSuffixOverrides(" VALUES (", ")", ",", () ->
          entity.insertColumns().stream().map(column ->
            ifTest(column.notNullTest(), () -> column.variables() + ",")
          ).collect(Collectors.joining(LF)));
      }
    });
  }
}

上面方法在执行时,最终拼接的 SQL 示例如下:

<script>
  INSERT INTO user
  <trim prefix="(" suffixOverrides="," suffix=")">
    <if test="id != null">
      id,
    </if>
    <if test="userName != null">
      name,
    </if>
    <if test="sex != null">
      sex,
    </if>
  </trim>
  <trim prefix=" VALUES (" suffixOverrides="," suffix=")">
    <if test="id != null">
      #{id},
    </if>
    <if test="userName != null">
      #{userName},
    </if>
    <if test="sex != null">
      #{sex},
    </if>
  </trim>
</script>

更多用法文档看 mybatis-mapper/mapper( gitee | GitHub )。

EntityTableEntityColumn

EntityTableEntityColumn 记录了实体类和表之间的映射信息和额外的很多配置信息。

这两个类中提供了大量便于在 XML 中使用的方法,例如: entity.insertColumns(),这个方法会把 insertable=false的排除后返回。

还有 EntityColumn::columnEqualsProperty 这样的方法返回 column = #{property} 形式的字符串。

为了使用上的统一,应该尽可能使用提供的现成方法,尽量避免自己拼接常用的字符串。

扩展

主要提供下面 3 个支持 SPI 扩展的接口:

  1. EntityClassFinder 如何找到执行方法的实体类类型
  2. EntityTableFactory 根据实体类构造 EntityTable 对象(表信息)
  3. EntityColumnFactory 根据实体类中的字段构建 EntityColumn 对象(列信息)

更具体的信息可以查看本项目中的默认实现,还有 mybatis-mapper/mapper( gitee | GitHub ) 中提供的 jpa 实现。

更复杂的还有一个兼容 tk-mapper 的项目:mybatis-mapper/tk-mapper( gitee | GitHub ) 的实现。

Caching - LanguageDriver

这是整个通用机制的核心,Caching 实现了 LanguageDriver 接口, 允许 Provider 方法的实现返回缓存后的方法 key, 在真正执行的时候,再从缓存中找到 SQL 真正执行。

为了让 Caching 生效,需要在接口方法添加 @Lang(Caching.class) 注解,例如:

class DemoMapper<T> {
  /**
   * 根据主键查询实体
   *
   * @param id 主键
   * @return 实体
   */
  @Lang(Caching.class)
  @SelectProvider(type = EntityProvider.class, method = "selectByPrimaryKey")
  Optional<T> selectByPrimaryKey(I id);
}
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