详解如何开发一个MyBatis通用Mapper的轮子
失足成万古风流人物 人气:0一、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。
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