开发一个MyBatis通用Mapper的轮子

一、前言

程序猿为什么如此执着于造轮子？MyBatis-Plus如此强大的工具流行这么多年了，我为啥还在重复造这样的轮子？

1、公司的技术规范不允许使用MyBatis-Plus，咱也不知道什么原因；

3、以前使用SpringDataJpa惯了，今年第一次用MyBatis，必须把它打造成我想要的样子；

6、MyBatis-Plus好像不支持联合主键；

7、还有一些其它的需求，比如对字典字段自动翻译：字典可能来自枚举、字典表、Redis......

10、通用数据权限控制；

11、如果不造此轮子，就没有这篇文章。

以上12点原因，便是造这个轮子的理由。实际上，轮子不重要，重要的是掌握轮子的原理，取其精华，去其糟粕。也欢迎大家拍砖，请轻拍，数学能力被谁拍坏了谁来陪。

二、需求

通用Mapper起码应该包含以下功能：

1、增

2、删

3、改

4、批量增

5、批量删

6、只更新指定字段

7、分页查询查当前页

8、分页查询查总数

9、字典字段翻译

10、数据权限控制

大概长下面这个样子：

public interface BaseMapper<T,K> {

    int insert(T t);

    int batchInsert(List<T> entity);

    int deleteById(K id);

    int deleteBatchIds(Collection<K> ids);

    int updateById(T entity);

    int updateSelectiveById(T entity);

    T selectById(K id);

    List<T> selectBatchIds(Collection<K> ids);

    List<T> selectAll();

    List<T> selectPage(PageRequest<T> pageRequest);

    Long selectCount(T entity);

}

三、实现原理

1、基于MyBatis3提供的SqlProvider构建动态Sql

例如如下代码：

@SelectProvider(type = UserSqlBuilder.class, method = "buildGetUsersByName")
List<User> getUsersByName(String name);

class UserSqlBuilder {
  public static String buildGetUsersByName(final String name) {
    return new SQL(){{
      SELECT("*");
      FROM("users");
      if (name != null) {
        WHERE("name like #{value} || '%'");
      }
      ORDER_BY("id");
    }}.toString();
  }
}

2、基于自定义注解，为实体和数据库表建立对应关系

例如如下代码：

@Table("user")
public class User {
    @Id(auto = true)
    @Column(value = "id")
    private Long id;

    @Column(value = "name", filterOperator = FilterOperator.LIKE)
    @OrderBy(orderPriority = 0)
    private String name;

    @OrderBy(order = Order.DESC, orderPriority = 1)
    private Integer age;

    private String email;

    @Transient
    private String test;
}

基于以上两个原理，当方法被调用时，我们便可构建出相应的动态Sql，从而实现该通用Mapper。

四、代码实现

1、自定义注解

1）@Table

了解Jpa的朋友一定很熟悉，这个就是为实体指定表名，实体不加这个注解就认为实体名与表名一致：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Table {
    //表名，不指定则使用实体类名
    String value() default "";
}

2）@Column

指定完表名，该指定列名了，同样的如果字段不指定则认为字段名与表列名一致：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Column {
    //对应数据库列名
    String value() default "";
    //查询时的过滤类型
    FilterOperator filterOperator() default FilterOperator.EQ;
    //是否查询，select是否带上该字段
    boolean selectable() default true;
    //是否插入，insert是否带上该字段
    boolean insertable() default true;
    //是否更新，update是否带上该字段
    boolean updatable() default true;
}

3）@Id

这个注解就是为了表明该字段是否是数据库主键。当然，这个注解可以与@Column合并，但为了更清晰，我还是决定单独使用这个注解。并且，也方便后期扩展。

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Id {
    //主键是否自动生成
    boolean auto() default false;
}

4）@OrderBy

这个注解来标明查询时的排序字段，同时考虑如果排序字段有多个，可定义优先级：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface OrderBy {
    //排序
    Order order() default Order.ASC;
    //多个排序字段先后顺序
    int orderPriority() default 0;
}

5）@Transient

考虑实体中有些字段在数据库中不存在的情况。使用这个注解来标注这样的字段：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Transient {
}

2、几个pojo，用来保存实体对应的信息

1）TableInfo，表示一个实体对应的数据库表信息

public class TableInfo {
    //表对应的实体类型
    private Class<?> entityClass;

    //表名
    private String tableName;

    //列
    private List<ColumnInfo> columns;

    //是否联合主键
    private boolean isUnionId;
}

2）ColumnInfo，表示实体中的一个字段对应的数据库表字段信息

public class ColumnInfo {
    //对应的java类型
    private Class<?> fieldClass;
    private Field field;
    private FilterOperator filterOperator;
    //数据库列
    private String column;
    //是否主键
    private boolean isPrimaryKey;
    //主键填充方式
    private boolean isPrimaryKeyAuto;
    //排序
    private Order orderBy;
    private int orderByPriority;
    //是否参与insert
    private boolean insertable;
    //是否参与update
    private boolean updatable;
    //是否参与select
    private boolean selectable;
}

以上只需要注意一点，如何判断一个实体是否是联合主键。这里用的比较粗暴的方法，如果有多个字段加了@Id，那么认为是联合主键。

3、定义开头说的BaseMapper

这个BaseMapper的定义模仿了SpringDataJpa，它需要两个泛型，T表示实体类型，K表示主键类型。

一般情况下K为简单数据类型，比如Long，String；

联合主键情况下，K为自定义的一个复杂数据类型，具体使用方法见文章最后章节。

public interface BaseMapper<T,K> {

    @InsertProvider(type = SqlProvider.class,method = "insert")
    @Options(useGeneratedKeys = true, keyProperty = "id",keyColumn = "id")
    int insert(T t);

    @InsertProvider(type = SqlProvider.class,method = "batchInsert")
    int batchInsert(@Param("list") List<T> entity);

    @DeleteProvider(type = SqlProvider.class,method = "deleteById")
    int deleteById(@Param("id") K id);

    @DeleteProvider(type = SqlProvider.class,method = "deleteBatchIds")
    int deleteBatchIds(@Param("ids") Collection<K> ids);

    @UpdateProvider(type = SqlProvider.class,method = "updateById")
    int updateById(T entity);

    @UpdateProvider(type = SqlProvider.class,method = "updateSelectiveById")
    int updateSelectiveById(T entity);

    @SelectProvider(type = SqlProvider.class,method = "selectById")
    T selectById(@Param("id") K id);

    @SelectProvider(type = SqlProvider.class,method = "selectBatchIds")
    List<T> selectBatchIds(@Param("ids") Collection<K> ids);

    @SelectProvider(type = SqlProvider.class,method = "selectAll")
    List<T> selectAll();

    @SelectProvider(type = SqlProvider.class,method = "selectPage")
    List<T> selectPage(PageRequest<T> pageRequest);

    @SelectProvider(type = SqlProvider.class,method = "selectCount")
    Long selectCount(T entity);

}

4、SqlProvider

public class SqlProvider<T> {
    private static Logger logger = LoggerFactory.getLogger(SqlProvider.class);
    private static Map<Class<?>, TableInfo> tableCache = new ConcurrentHashMap<>();

    public String insert(T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        String intoColumns = tableInfo.getColumns()
                .stream()
                .filter(ColumnInfo::isInsertable)
                .map(ColumnInfo::getColumn)
                .collect(Collectors.joining(","));
        String values = tableInfo.getColumns()
                .stream()
                .filter(ColumnInfo::isInsertable)
                .map(ColumnInfo::variable)
                .collect(Collectors.joining(","));
        String sql = new SQL()
                .INSERT_INTO(tableName)
                .INTO_COLUMNS(intoColumns)
                .INTO_VALUES(values).toString();
        logger.info("sql->{},params->{}",sql,entity);
        return sql;
    }

    public String batchInsert(@Param("list" ) List<?> entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        String intoColumns = tableInfo.getColumns()
                .stream()
                .filter(ColumnInfo::isInsertable)
                .map(ColumnInfo::getColumn)
                .collect(Collectors.joining(","));
        String values = tableInfo.getColumns()
                .stream()
                .filter(ColumnInfo::isInsertable)
                .map(column->column.variableWithPrefix("item"))
                .collect(Collectors.joining(","));
        String sql = new SQL()
                .INSERT_INTO(tableName)
                .INTO_COLUMNS(intoColumns).toString();
        sql += " values ";
        sql += "<foreach collection=\"list\" item=\"item\" separator=\",\">" +
                "  <trim prefix=\"(\" suffix=\")\" suffixOverrides=\",\">" +
                "    " + values +
                "  </trim>" +
                "</foreach>";
        sql = "<script>"+sql+"</script>";
        logger.info("sql->{},params->{}",sql,entity);
        return sql;
    }

    public String deleteById(@Param("id") T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        String[] where = null;
        if (tableInfo.isUnionId()){
            where = tableInfo.getColumns()
                    .stream()
                    .filter(ColumnInfo::isPrimaryKey)
                    .map(columnInfo -> columnInfo.getColumn()+" = #{id."+columnInfo.getField().getName()+"}")
                    .toArray(String[]::new);
        }else {
            where = tableInfo.getColumns()
                    .stream()
                    .filter(ColumnInfo::isPrimaryKey)
                    .map(columnInfo -> columnInfo.getColumn()+" = #{id}")
                    .toArray(String[]::new);
        }
        String sql = new SQL()
                .DELETE_FROM(tableName)
                .WHERE(where)
                .toString();
        logger.info("sql->{},params->{}",sql,entity);
        return sql;
    }

    public String deleteBatchIds(@Param("ids") Collection<?> entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        if (tableInfo.isUnionId()){
            String[] where = new String[entity.size()];
            for (int i = 0; i < entity.size(); i++){
                List<String> list = new ArrayList<>();
                String s = "%s=#{ids[%d].%s}";
                for (ColumnInfo columnInfo:tableInfo.getColumns()){
                    if (columnInfo.isPrimaryKey()){
                        list.add(String.format(s,columnInfo.getColumn(),i,columnInfo.getField().getName()));
                    }
                }
                where[i] = "("+StringUtils.join(list," and ")+")";
            }
            String sql = "delete from %s where %s ";
            sql = String.format(sql,tableName,StringUtils.join(where," or "));
            logger.info("sql->{},params->{}",sql,entity);
            return sql;
        }else {
            String idName = tableInfo.getColumns()
                    .stream()
                    .filter(ColumnInfo::isPrimaryKey)
                    .findFirst()
                    .get()
                    .getColumn();
            String sql = "DELETE FROM %s WHERE %s IN (%s) ";
            String[] arr = new String[entity.size()];
            for (int i = 0; i < entity.size(); i++){
                arr[i] = "#{ids["+i+"]}";
            }
            sql = String.format(sql,tableName,idName,StringUtils.join(arr,","));
            logger.info("sql->{},params->{}",sql,entity);
            return sql;
        }
    }

    public String updateById(T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        String[] where = tableInfo.getColumns()
                .stream()
                .filter(ColumnInfo::isPrimaryKey)
                .map(columnInfo -> columnInfo.getColumn()+" = "+columnInfo.variable())
                .toArray(String[]::new);
        String sql = new SQL().UPDATE(tableName).SET(tableInfo.updateSetColumn()).WHERE(where).toString();
        logger.info("sql->{},params->{}",sql,entity);
        return sql;
    }

    public String updateSelectiveById(T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        String[] where = tableInfo.getColumns()
                .stream()
                .filter(ColumnInfo::isPrimaryKey)
                .map(columnInfo -> columnInfo.getColumn()+" = "+columnInfo.variable())
                .toArray(String[]::new);
        String sql = new SQL().UPDATE(tableName).SET(tableInfo.updateSetSelectiveColumn(entity)).WHERE(where).toString();
        logger.info("sql->{},params->{}",sql,entity);
        return sql;
    }

    public String selectById(@Param("id")T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String[] where = null;
        if (tableInfo.isUnionId()){
            where = tableInfo.getColumns().stream().filter(ColumnInfo::isPrimaryKey)
                    .map(columnInfo -> columnInfo.getColumn()+" = #{id."+columnInfo.getField().getName()+"}")
                    .toArray(String[]::new);
        }else {
            where = tableInfo.getColumns().stream().filter(ColumnInfo::isPrimaryKey)
                    .map(columnInfo -> columnInfo.getColumn()+" = #{id}")
                    .toArray(String[]::new);
        }
        String sql = new SQL()
                .SELECT(tableInfo.selectColumnAsProperty())
                .FROM(tableInfo.getTableName())
                .WHERE(where)
                .toString();
        logger.info("sql->{},params->{}",sql,entity);
        return sql;
    }

    public String selectBatchIds(@Param("ids")Collection<?> entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        String tableName = tableInfo.getTableName();
        if (tableInfo.isUnionId()){
            String[] where = new String[entity.size()];
            for (int i = 0; i < entity.size(); i++){
                List<String> list = new ArrayList<>();
                String s = "%s=#{ids[%d].%s}";
                for (ColumnInfo columnInfo:tableInfo.getColumns()){
                    if (columnInfo.isPrimaryKey()){
                        list.add(String.format(s,columnInfo.getColumn(),i,columnInfo.getField().getName()));
                    }
                }
                where[i] = "("+StringUtils.join(list," and ")+")";
            }
            String sql = "select %s from %s where %s";
            sql = String.format(sql,tableInfo.selectColumnAsProperty(),tableInfo.getTableName(),StringUtils.join(where," or "));
            logger.info("sql->{},params->{}",sql,entity);
            return sql;
        }else {
            String idName = tableInfo.getColumns()
                    .stream()
                    .filter(ColumnInfo::isPrimaryKey)
                    .findFirst()
                    .get()
                    .getColumn();
            String sql = "select %s from %s where %s in (%s) ";
            String[] arr = new String[entity.size()];
            for (int i = 0; i < entity.size(); i++){
                arr[i] = "#{ids["+i+"]}";
            }
            sql = String.format(sql,tableInfo.selectColumnAsProperty(),tableName,idName,StringUtils.join(arr,","));
            logger.info("sql->{},params->{}",sql,entity);
            return sql;
        }
    }

    public String selectAll(T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        SQL sql =  new SQL()
                .SELECT(tableInfo.selectColumnAsProperty())
                .FROM(tableInfo.getTableName());
        String orderBy = tableInfo.orderByColumn();
        if (StringUtils.isNotEmpty(orderBy)){
            sql.ORDER_BY(orderBy);
        }
        return sql.toString();
    }

    public String selectPage(PageRequest<T> entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        SQL sql = new SQL()
                .SELECT(tableInfo.selectColumnAsProperty())
                .FROM(tableInfo.getTableName());
        String[] where = tableInfo.getColumns().stream()
                .filter(column -> {
                    Field field = column.getField();
                    T bean = entity.getPageParams();
                    Object value = Util.getFieldValue(bean, field);
                    if (value == null) {
                        return false;
                    }
                    return StringUtils.isNotEmpty(value.toString());
                })
                .map(column -> {
                    String param = " #{pageParams." + column.getField().getName()+"}";
                    if (column.getFilterOperator() == FilterOperator.LIKE){
                        param = "concat('%', "+param+", '%')";
                    }
                    if (column.getFilterOperator() == FilterOperator.LEFTLIKE){
                        param = "concat("+param+", '%')";
                    }
                    if (column.getFilterOperator() == FilterOperator.RIGHTLIKE){
                        param = "concat('%', "+param+")";
                    }
                    return column.getColumn()+column.filterOperator()+param;
                })
                .toArray(String[]::new);
        sql.WHERE(where);
        if (StringUtils.isNotEmpty(entity.getOrder())){
            ColumnInfo columnInfo = tableInfo.getColumns().stream()
                    .filter(columnInfo1 -> columnInfo1.getField().getName().equalsIgnoreCase(entity.getOrder()))
                    .findFirst().orElse(null);
            if (columnInfo != null){
                String direction = entity.getOrderDirection();
                direction = (StringUtils.isEmpty(direction) || direction.equalsIgnoreCase("asc"))?" asc ":" desc ";
                sql.ORDER_BY(columnInfo.getColumn() + direction);
            }
        }else {
            String orderBy = tableInfo.orderByColumn();
            if (StringUtils.isNotEmpty(orderBy)){
                sql.ORDER_BY(orderBy);
            }
        }
        sql.OFFSET("#{offset}").LIMIT("#{pageSize}");
        String s = sql.toString();
        logger.info("sql->{},params->{}",s,entity);
        return s;
    }

    public String selectCount(T entity, ProviderContext context){
        TableInfo tableInfo = getTableInfo(context);
        SQL sql = new SQL()
                .SELECT("count(1)")
                .FROM(tableInfo.getTableName());
        String[] where = tableInfo.getColumns().stream()
                .filter(column -> {
                    Field field = column.getField();
                    Object value = Util.getFieldValue(entity, field);
                    if (value == null) {
                        return false;
                    }
                    return StringUtils.isNotEmpty(value.toString());
                })
                .map(column -> {
                    String param = " #{" + column.getField().getName()+"}";
                    if (column.getFilterOperator() == FilterOperator.LIKE){
                        param = "concat('%', "+param+", '%')";
                    }
                    if (column.getFilterOperator() == FilterOperator.LEFTLIKE){
                        param = "concat("+param+", '%')";
                    }
                    if (column.getFilterOperator() == FilterOperator.RIGHTLIKE){
                        param = "concat('%', "+param+")";
                    }
                    return column.getColumn()+column.filterOperator()+param;
                })
                .toArray(String[]::new);
        sql.WHERE(where);
        String s = sql.toString();
        logger.info("sql->{},params->{}",s,entity);
        return s;
    }

    private TableInfo getTableInfo(ProviderContext context){
        Class<?> clz = getEntityType(context);
        return tableCache.computeIfAbsent(context.getMapperType(), t-> Util.tableInfo(clz));
    }

    private Class<?> getEntityType(ProviderContext context) {
        return Stream.of(context.getMapperType().getGenericInterfaces())
                .filter(ParameterizedType.class::isInstance)
                .map(ParameterizedType.class::cast)
                .filter(type -> type.getRawType() == BaseMapper.class)
                .findFirst()
                .map(type -> type.getActualTypeArguments()[0])
                .filter(Class.class::isInstance)
                .map(Class.class::cast)
                .orElseThrow(() -> new IllegalStateException("未找到BaseMapper的泛型类 " + context.getMapperType().getName() + "."));
    }

}

5、实体类转TableInfo

public static TableInfo tableInfo(Class<?> entityClass) {
        TableInfo info = new TableInfo();
        info.setEntityClass(entityClass);
        Table table = entityClass.getAnnotation(Table.class);
        String tableName = entityClass.getSimpleName();
        if (table != null && StringUtils.isNotEmpty(table.value())){
            tableName = table.value();
        }
        info.setTableName(tableName);
        Field[] allFields = getFields(entityClass);
        Field[] fields = Stream.of(allFields)
                //过滤@Transient注解的field
                .filter(field -> !field.isAnnotationPresent(Transient.class))
                .toArray(Field[]::new);
        List<ColumnInfo> columns = new ArrayList<>();
        int idCount = 0;
        for (Field field:fields){
            ColumnInfo columnInfo = new ColumnInfo();
            columnInfo.setFieldClass(field.getDeclaringClass());
            columnInfo.setField(field);
            Id id = field.getAnnotation(Id.class);
            idCount = idCount + (id == null?0:1);
            columnInfo.setPrimaryKey(id == null?Boolean.FALSE:Boolean.TRUE);
            columnInfo.setPrimaryKeyAuto(id == null?Boolean.FALSE:id.auto());
            Column column = field.getAnnotation(Column.class);
            String columnName = field.getName();
            if (column != null && StringUtils.isNotEmpty(column.value())){
                columnName = column.value();
            }
            columnInfo.setColumn(columnName);
            FilterOperator filterOperator = FilterOperator.EQ;
            if (column != null && column.filterOperator() != null){
                filterOperator = column.filterOperator();
            }
            columnInfo.setFilterOperator(filterOperator);

            if (columnInfo.isPrimaryKeyAuto()){
                columnInfo.setInsertable(false);
            }else {
                columnInfo.setInsertable(true);
                if (column != null){
                    columnInfo.setInsertable(column.insertable());
                }
            }
            columnInfo.setUpdatable(true);
            columnInfo.setSelectable(true);
            if (column != null){
                columnInfo.setSelectable(column.selectable());
                columnInfo.setUpdatable(column.updatable());
            }
            OrderBy orderBy = field.getAnnotation(OrderBy.class);
            if (orderBy != null){
                columnInfo.setOrderBy(orderBy.order());
                columnInfo.setOrderByPriority(orderBy.orderPriority());
            }
            columns.add(columnInfo);
        }
        if (idCount > 1){
            info.setUnionId(Boolean.TRUE);
        }
        info.setColumns(columns);
        return info;
    }

6、字典字段自动翻译

简单实现思路：对需要翻译的字段加上@FieldTrans注解来表明这个字段需要翻译，通过AOP方式对结果数据进行增强，来将字段进行翻译更新。

此部分内容留待后续实现，同时调研一下是否还有更优雅简单的实现方式。

7、数据权限

我们先来思考一下数据权限到底要干啥？一句话来概括：查一张表的数据时在where条件中追加“and 控制权限的列 in (???)”。

简单实现方法：在控制权限的字段加上@DataAuthrity注解来表明通过这个字段控制权限，而???的内容肯定是由业务代码来生成的，因此考虑给这个注解增加一个属性，用来指明权限数据由执行哪个接口或方法来获取。

此部分内容留待后续实现，同时调研一下是否还有更优雅简单的实现方式。

五、使用示例

1、数据库表

CREATE TABLE `user` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `email` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

2、实体

@Table("user")
public class User {
    @Id(auto = true)
    @Column(value = "id")
    private Long id;

    @Column(value = "name", filterOperator = FilterOperator.LIKE)
    @OrderBy(orderPriority = 0)
    private String name;

    @OrderBy(order = Order.DESC, orderPriority = 1)
    private Integer age;

    private String email;

    @Transient
    private String test;
}

3、Mapper

public interface UserMapper extends BaseMapper<User, Long> {

}

至此，不需要写任何mapper.xml，UserMapper已经具备了增删改查能力。

4、联合主键示例

public class User1 {
    @Id
    @Column(value = "id1")
    private String id1;

    @Id
    @Column(value = "id2")
    private String id2;

    @Column(value = "name", filterOperator = FilterOperator.LIKE)
    @OrderBy(orderPriority = 0)
    private String name;

    @OrderBy(order = Order.DESC, orderPriority = 1)
    private Integer age;

    private String email;

    @Transient
    private String test;
}

public class User1Id {
    private String id1;
    private String id2;
}

public interface User1Mapper extends BaseMapper<User1,User1Id> {
}

六、总结

本轮子目前基本上不值一提，但相信后面我再把字典翻译、通用数据权限加上的话，仍然会不值一提。

实际上轮子本身不重要，开发过程中的各种思考、试验更重要吧。

欢迎阅读，欢迎转载，转载请注明出处，求你了。