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30 个类手写 Spring 核心原理之自定义 ORM(上)(6)

作者:Tom弹架构
  • 2021 年 12 月 16 日
  • 本文字数:12993 字

    阅读完需:约 43 分钟

本文节选自《Spring 5 核心原理》

1 实现思路概述

1.1 从 ResultSet 说起

说到 ResultSet,有 Java 开发经验的“小伙伴”自然最熟悉不过了,不过我相信对于大多数人来说也算是“最熟悉的陌生人”。从 ResultSet 取值操作大家都会,比如:



private static List<Member> select(String sql) { List<Member> result = new ArrayList<>(); Connection con = null; PreparedStatement pstm = null; ResultSet rs = null; try { //1. 加载驱动类 Class.forName("com.mysql.jdbc.Driver"); //2. 建立连接 con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-demo", "root","123456"); //3. 创建语句集 pstm = con.prepareStatement(sql); //4. 执行语句集 rs = pstm.executeQuery(); while (rs.next()){ Member instance = new Member(); instance.setId(rs.getLong("id")); instance.setName(rs.getString("name")); instance.setAge(rs.getInt("age")); instance.setAddr(rs.getString("addr")); result.add(instance); } //5. 获取结果集 }catch (Exception e){ e.printStackTrace(); } //6. 关闭结果集、关闭语句集、关闭连接 finally { try { rs.close(); pstm.close(); con.close(); }catch (Exception e){ e.printStackTrace(); } } return result;}
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以上我们在没有使用框架以前的常规操作。随着业务和开发量的增加,在数据持久层这样的重复代码出现频次非常高。因此,我们就想到将非功能性代码和业务代码进行分离。我们首先想到将 ResultSet 封装数据的代码逻辑分离,增加一个 mapperRow()方法,专门处理对结果的封装,代码如下:



private static List<Member> select(String sql) { List<Member> result = new ArrayList<>(); Connection con = null; PreparedStatement pstm = null; ResultSet rs = null; try { //1. 加载驱动类 Class.forName("com.mysql.jdbc.Driver"); //2. 建立连接 con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-demo", "root","123456"); //3. 创建语句集 pstm = con.prepareStatement(sql); //4. 执行语句集 rs = pstm.executeQuery(); while (rs.next()){ Member instance = mapperRow(rs,rs.getRow()); result.add(instance); } //5. 获取结果集 }catch (Exception e){ e.printStackTrace(); } //6. 关闭结果集、关闭语句集、关闭连接 finally { try { rs.close(); pstm.close(); con.close(); }catch (Exception e){ e.printStackTrace(); } } return result;}
private static Member mapperRow(ResultSet rs, int i) throws Exception { Member instance = new Member(); instance.setId(rs.getLong("id")); instance.setName(rs.getString("name")); instance.setAge(rs.getInt("age")); instance.setAddr(rs.getString("addr")); return instance;}
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但在真实的业务场景中,这样的代码逻辑重复率实在太高,上面的改造只能应用 Member 类,换一个实体类又要重新封装,聪明的程序员肯定不会通过纯体力劳动给每一个实体类写一个 mapperRow()方法,一定会想到代码复用方案。我们不妨来做这样一个改造。先创建 Member 类:



package com.gupaoedu.vip.orm.demo.entity;
import lombok.Data;
import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.Table;import java.io.Serializable;
@Entity@Table(name="t_member")@Datapublic class Member implements Serializable { @Id private Long id; private String name; private String addr; private Integer age;
@Override public String toString() { return "Member{" + "id=" + id + ", name='" + name + '\'' + ", addr='" + addr + '\'' + ", age=" + age + '}'; }}
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优化 JDBC 操作:



public static void main(String[] args) { Member condition = new Member(); condition.setName("Tom"); condition.setAge(19); List<?> result = select(condition); System.out.println(Arrays.toString(result.toArray()));}
private static List<?> select(Object condition) {
List<Object> result = new ArrayList<>();
Class<?> entityClass = condition.getClass();
Connection con = null; PreparedStatement pstm = null; ResultSet rs = null; try { //1. 加载驱动类 Class.forName("com.mysql.jdbc.Driver"); //2. 建立连接 con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-demo? characterEncoding=UTF-8&rewriteBatchedStatements=true","root","123456");
//根据类名找属性名 Map<String,String> columnMapper = new HashMap<String,String>(); //根据属性名找字段名 Map<String,String> fieldMapper = new HashMap<String,String>(); Field[] fields = entityClass.getDeclaredFields(); for (Field field : fields) { field.setAccessible(true); String fieldName = field.getName(); if(field.isAnnotationPresent(Column.class)){ Column column = field.getAnnotation(Column.class); String columnName = column.name(); columnMapper.put(columnName,fieldName); fieldMapper.put(fieldName,columnName); }else { //默认就是字段名、属性名一致 columnMapper.put(fieldName, fieldName); fieldMapper.put(fieldName,fieldName); } }
//3. 创建语句集 Table table = entityClass.getAnnotation(Table.class); String sql = "select * from " + table.name();
StringBuffer where = new StringBuffer(" where 1=1 "); for (Field field : fields) { Object value =field.get(condition); if(null != value){ if(String.class == field.getType()) { where.append(" and " + fieldMapper.get(field.getName()) + " = '" + value + "'"); }else{ where.append(" and " + fieldMapper.get(field.getName()) + " = " + value + ""); } //其他的在这里就不一一列举,后面我们手写ORM框架时会完善 } } System.out.println(sql + where.toString()); pstm = con.prepareStatement(sql + where.toString());
//4. 执行语句集 rs = pstm.executeQuery();
//元数据? //保存了处理真正数值以外的所有附加信息 int columnCounts = rs.getMetaData().getColumnCount(); while (rs.next()){ Object instance = entityClass.newInstance(); for (int i = 1; i <= columnCounts; i++) { //实体类属性名,对应数据库表的字段名 //可以通过反射机制拿到实体类的所有字段
//从rs中取得当前这个游标下的类名 String columnName = rs.getMetaData().getColumnName(i); //有可能是私有的 Field field = entityClass.getDeclaredField(columnMapper.get(columnName)); field.setAccessible(true); field.set(instance,rs.getObject(columnName)); }
result.add(instance);
}
//5. 获取结果集 }catch (Exception e){ e.printStackTrace(); } //6. 关闭结果集、关闭语句集、关闭连接 finally { try { rs.close(); pstm.close(); con.close(); }catch (Exception e){ e.printStackTrace(); } }
return result;}
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上面巧妙地利用反射机制读取 Class 信息和 Annotation 信息,将数据库表中的列和类中的字段进行关联映射并赋值,以减少重复代码。

1.2 为什么需要 ORM 框架

通过前面的讲解,我们已经了解 ORM 框架的基本实现原理。ORM 是指对象关系映射(Object Relation Mapping),映射的不只是对象值,还有对象与对象之间的关系,例如一对多、多对多、一对一这样的表关系。现在市面上 ORM 框架也非常多,有大家所熟知的 Hibernate、Spring JDBC、MyBatis、JPA 等。在这里做一个简单的总结,如下表所示。



既然市面上有这么多选择,我为什么还要自己写 ORM 框架呢?这得从我的一次空降担任架构师的经验说起。空降面临最大的难题就是如何取得团队“小伙伴们”的信任。当时,团队总共就 8 人,每个人的水平参差不齐,甚至有些人还没接触过 MySQL,诸如 Redis 等缓存中间件更不用说了。基本只会使用 Hibernate 的 CRUD,而且已经影响到了系统性能。由于工期紧张,没有时间和精力给团队做系统培训,也为了兼顾可控性,于是就产生了自研 ORM 框架的想法。我做了这样的顶层设计,以降低团队“小伙伴们”的存息成本,顶层接口统一参数、统一返回值,具体如下。


**(1)规定查询方法的接口模型为: **



/** * 获取列表 * @param queryRule 查询条件 * @return */List<T> select(QueryRule queryRule) throws Exception;
/** * 获取分页结果 * @param queryRule 查询条件 * @param pageNo 页码 * @param pageSize 每页条数 * @return */Page<?> select(QueryRule queryRule,int pageNo,int pageSize) throws Exception;
/** * 根据SQL获取列表 * @param sql SQL语句 * @param args 参数 * @return */List<Map<String,Object>> selectBySql(String sql, Object... args) throws Exception;
/** * 根据SQL获取分页 * @param sql SQL语句 * @param pageNo 页码 * @param pageSize 每页条数 * @return */Page<Map<String,Object>> selectBySqlToPage(String sql, Object [] param, int pageNo, int pageSize) throws Exception;
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(2)规定删除方法的接口模型为:



/** * 删除一条记录 * @param entity entity中的ID不能为空,如果ID为空,其他条件不能为空,都为空不予执行 * @return */boolean delete(T entity) throws Exception;
/** * 批量删除 * @param list * @return 返回受影响的行数 * @throws Exception */int deleteAll(List<T> list) throws Exception;
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(3)规定插入方法的接口模型为:



/** * 插入一条记录并返回插入后的ID * @param entity 只要entity不等于null,就执行插入 * @return */PK insertAndReturnId(T entity) throws Exception;
/** * 插入一条记录自增ID * @param entity * @return * @throws Exception */boolean insert(T entity) throws Exception;
/** * 批量插入 * @param list * @return 返回受影响的行数 * @throws Exception */int insertAll(List<T> list) throws Exception;
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(4)规定修改方法的接口模型为:



/** * 修改一条记录 * @param entity entity中的ID不能为空,如果ID为空,其他条件不能为空,都为空不予执行 * @return * @throws Exception */boolean update(T entity) throws Exception;
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利用这套基础的 API,后面我又基于 Redis、MongoDB、ElasticSearch、Hive、HBase 各封装了一套,以此来降低团队的学习成本,也大大提升了程序的可控性,更方便统一监控。

2 搭建基础架构

2.1 Page

定义 Page 类的主要目的是为后面的分页查询统一返回结果做顶层支持,其主要功能包括分页逻辑的封装、分页数据。



package javax.core.common;
import java.io.Serializable;import java.util.ArrayList;import java.util.List;
/** * 分页对象,包含当前页数据及分页信息,如总记录数 * 能够支持和JQuery EasyUI直接对接,能够支持和BootStrap Table直接对接 */public class Page<T> implements Serializable {
private static final long serialVersionUID = 1L; private static final int DEFAULT_PAGE_SIZE = 20;
private int pageSize = DEFAULT_PAGE_SIZE; //每页的记录数
private long start; //当前页第一条数据在List中的位置,从0开始
private List<T> rows; //当前页中存放的记录,类型一般为List
private long total; //总记录数
/** * 构造方法,只构造空页 */ public Page() { this(0, 0, DEFAULT_PAGE_SIZE, new ArrayList<T>()); }
/** * 默认构造方法 * * @param start 本页数据在数据库中的起始位置 * @param totalSize 数据库中总记录条数 * @param pageSize 本页容量 * @param rows 本页包含的数据 */ public Page(long start, long totalSize, int pageSize, List<T> rows) { this.pageSize = pageSize; this.start = start; this.total = totalSize; this.rows = rows; }
/** * 取总记录数 */ public long getTotal() { return this.total; } public void setTotal(long total) { this.total = total; }
/** * 取总页数 */ public long getTotalPageCount() { if (total % pageSize == 0){ return total / pageSize; }else{ return total / pageSize + 1; } }
/** * 取每页数据容量 */ public int getPageSize() { return pageSize; }
/** * 取当前页中的记录 */ public List<T> getRows() { return rows; } public void setRows(List<T> rows) { this.rows = rows; }
/** * 取该页的当前页码,页码从1开始 */ public long getPageNo() { return start / pageSize + 1; }
/** * 该页是否有下一页 */ public boolean hasNextPage() { return this.getPageNo() < this.getTotalPageCount() - 1; }
/** * 该页是否有上一页 */ public boolean hasPreviousPage() { return this.getPageNo() > 1; }
/** * 获取任意一页第一条数据在数据集中的位置,每页条数使用默认值 * * @see #getStartOfPage(int,int) */ protected static int getStartOfPage(int pageNo) { return getStartOfPage(pageNo, DEFAULT_PAGE_SIZE); }
/** * 获取任意一页第一条数据在数据集中的位置 * * @param pageNo 从1开始的页号 * @param pageSize 每页记录条数 * @return 该页第一条数据 */ public static int getStartOfPage(int pageNo, int pageSize) { return (pageNo - 1) * pageSize; }
}
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2.2 ResultMsg

ResultMsg 类主要是为统一返回结果做的顶层设计,主要包括状态码、结果说明内容和返回数据。



package javax.core.common;
import java.io.Serializable;
//底层设计public class ResultMsg<T> implements Serializable {
private static final long serialVersionUID = 2635002588308355785L;
private int status; //状态码,系统的返回码 private String msg; //状态码的解释 private T data; //放任意结果
public ResultMsg() {} public ResultMsg(int status) { this.status = status; }
public ResultMsg(int status, String msg) { this.status = status; this.msg = msg; } public ResultMsg(int status, T data) { this.status = status; this.data = data; }
public ResultMsg(int status, String msg, T data) { this.status = status; this.msg = msg; this.data = data; }
public int getStatus() { return status; }
public void setStatus(int status) { this.status = status; }
public String getMsg() { return msg; }
public void setMsg(String msg) { this.msg = msg; }
public T getData() { return data; }
public void setData(T data) { this.data = data; }
}
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2.3 BaseDao

作为所有 BaseDao 持久化框架的顶层接口,主要定义增、删、改、查统一的参数列表和返回值。



package javax.core.common.jdbc;
import com.gupaoedu.vip.orm.framework.QueryRule;
import javax.core.common.Page;import java.util.List;import java.util.Map;
public interface BaseDao<T,PK> { /** * 获取列表 * @param queryRule 查询条件 * @return */ List<T> select(QueryRule queryRule) throws Exception;
/** * 获取分页结果 * @param queryRule 查询条件 * @param pageNo 页码 * @param pageSize 每页条数 * @return */ Page<?> select(QueryRule queryRule,int pageNo,int pageSize) throws Exception;
/** * 根据SQL获取列表 * @param sql SQL语句 * @param args 参数 * @return */ List<Map<String,Object>> selectBySql(String sql, Object... args) throws Exception;
/** * 根据SQL获取分页 * @param sql SQL语句 * @param pageNo 页码 * @param pageSize 每页条数 * @return */ Page<Map<String,Object>> selectBySqlToPage(String sql, Object [] param, int pageNo, int pageSize) throws Exception;
/** * 删除一条记录 * @param entity entity中的ID不能为空,如果ID为空,其他条件不能为空,都为空则不予执行 * @return */ boolean delete(T entity) throws Exception;
/** * 批量删除 * @param list * @return 返回受影响的行数 * @throws Exception */ int deleteAll(List<T> list) throws Exception;
/** * 插入一条记录并返回插入后的ID * @param entity 只要entity不等于null,就执行插入操作 * @return */ PK insertAndReturnId(T entity) throws Exception;
/** * 插入一条记录自增ID * @param entity * @return * @throws Exception */ boolean insert(T entity) throws Exception;
/** * 批量插入 * @param list * @return 返回受影响的行数 * @throws Exception */ int insertAll(List<T> list) throws Exception;
/** * 修改一条记录 * @param entity entity中的ID不能为空,如果ID为空,其他条件不能为空,都为空则不予执行 * @return * @throws Exception */ boolean update(T entity) throws Exception;}
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2.4 QueryRule

如果用 QueryRule 类来构建查询条件,用户在做条件查询时不需要手写 SQL,实现业务代码与 SQL 解耦。



package com.gupaoedu.vip.orm.framework;
import java.io.Serializable;import java.util.ArrayList;import java.util.List;
/** * QueryRule,主要功能用于构造查询条件 */public final class QueryRule implements Serializable{ private static final long serialVersionUID = 1L; public static final int ASC_ORDER = 101; public static final int DESC_ORDER = 102; public static final int LIKE = 1; public static final int IN = 2; public static final int NOTIN = 3; public static final int BETWEEN = 4; public static final int EQ = 5; public static final int NOTEQ = 6; public static final int GT = 7; public static final int GE = 8; public static final int LT = 9; public static final int LE = 10; public static final int ISNULL = 11; public static final int ISNOTNULL = 12; public static final int ISEMPTY = 13; public static final int ISNOTEMPTY = 14; public static final int AND = 201; public static final int OR = 202; private List<Rule> ruleList = new ArrayList<Rule>(); private List<QueryRule> queryRuleList = new ArrayList<QueryRule>(); private String propertyName;
private QueryRule() {}
private QueryRule(String propertyName) { this.propertyName = propertyName; }
public static QueryRule getInstance() { return new QueryRule(); } /** * 添加升序规则 * @param propertyName * @return */ public QueryRule addAscOrder(String propertyName) { this.ruleList.add(new Rule(ASC_ORDER, propertyName)); return this; }
/** * 添加降序规则 * @param propertyName * @return */ public QueryRule addDescOrder(String propertyName) { this.ruleList.add(new Rule(DESC_ORDER, propertyName)); return this; }
public QueryRule andIsNull(String propertyName) { this.ruleList.add(new Rule(ISNULL, propertyName).setAndOr(AND)); return this; }
public QueryRule andIsNotNull(String propertyName) { this.ruleList.add(new Rule(ISNOTNULL, propertyName).setAndOr(AND)); return this; }
public QueryRule andIsEmpty(String propertyName) { this.ruleList.add(new Rule(ISEMPTY, propertyName).setAndOr(AND)); return this; }
public QueryRule andIsNotEmpty(String propertyName) { this.ruleList.add(new Rule(ISNOTEMPTY, propertyName).setAndOr(AND)); return this; }
public QueryRule andLike(String propertyName, Object value) { this.ruleList.add(new Rule(LIKE, propertyName, new Object[] { value }).setAndOr(AND)); return this; }
public QueryRule andEqual(String propertyName, Object value) { this.ruleList.add(new Rule(EQ, propertyName, new Object[] { value }).setAndOr(AND)); return this; }
public QueryRule andBetween(String propertyName, Object... values) { this.ruleList.add(new Rule(BETWEEN, propertyName, values).setAndOr(AND)); return this; }
public QueryRule andIn(String propertyName, List<Object> values) { this.ruleList.add(new Rule(IN, propertyName, new Object[] { values }).setAndOr(AND)); return this; }
public QueryRule andIn(String propertyName, Object... values) { this.ruleList.add(new Rule(IN, propertyName, values).setAndOr(AND)); return this; } public QueryRule andNotIn(String propertyName, List<Object> values) { this.ruleList.add(new Rule(NOTIN, propertyName, new Object[] { values }).setAndOr(AND)); return this; }
public QueryRule orNotIn(String propertyName, Object... values) { this.ruleList.add(new Rule(NOTIN, propertyName, values).setAndOr(OR)); return this; }
public QueryRule andNotEqual(String propertyName, Object value) { this.ruleList.add(new Rule(NOTEQ, propertyName, new Object[] { value }).setAndOr(AND)); return this; }
public QueryRule andGreaterThan(String propertyName, Object value) { this.ruleList.add(new Rule(GT, propertyName, new Object[] { value }).setAndOr(AND)); return this; }
public QueryRule andGreaterEqual(String propertyName, Object value) { this.ruleList.add(new Rule(GE, propertyName, new Object[] { value }).setAndOr(AND)); return this; }
public QueryRule andLessThan(String propertyName, Object value) { this.ruleList.add(new Rule(LT, propertyName, new Object[] { value }).setAndOr(AND)); return this; }
public QueryRule andLessEqual(String propertyName, Object value) { this.ruleList.add(new Rule(LE, propertyName, new Object[] { value }).setAndOr(AND)); return this; } public QueryRule orIsNull(String propertyName) { this.ruleList.add(new Rule(ISNULL, propertyName).setAndOr(OR)); return this; }
public QueryRule orIsNotNull(String propertyName) { this.ruleList.add(new Rule(ISNOTNULL, propertyName).setAndOr(OR)); return this; }
public QueryRule orIsEmpty(String propertyName) { this.ruleList.add(new Rule(ISEMPTY, propertyName).setAndOr(OR)); return this; }
public QueryRule orIsNotEmpty(String propertyName) { this.ruleList.add(new Rule(ISNOTEMPTY, propertyName).setAndOr(OR)); return this; }
public QueryRule orLike(String propertyName, Object value) { this.ruleList.add(new Rule(LIKE, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public QueryRule orEqual(String propertyName, Object value) { this.ruleList.add(new Rule(EQ, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public QueryRule orBetween(String propertyName, Object... values) { this.ruleList.add(new Rule(BETWEEN, propertyName, values).setAndOr(OR)); return this; }
public QueryRule orIn(String propertyName, List<Object> values) { this.ruleList.add(new Rule(IN, propertyName, new Object[] { values }).setAndOr(OR)); return this; }
public QueryRule orIn(String propertyName, Object... values) { this.ruleList.add(new Rule(IN, propertyName, values).setAndOr(OR)); return this; }
public QueryRule orNotEqual(String propertyName, Object value) { this.ruleList.add(new Rule(NOTEQ, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public QueryRule orGreaterThan(String propertyName, Object value) { this.ruleList.add(new Rule(GT, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public QueryRule orGreaterEqual(String propertyName, Object value) { this.ruleList.add(new Rule(GE, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public QueryRule orLessThan(String propertyName, Object value) { this.ruleList.add(new Rule(LT, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public QueryRule orLessEqual(String propertyName, Object value) { this.ruleList.add(new Rule(LE, propertyName, new Object[] { value }).setAndOr(OR)); return this; }
public List<Rule> getRuleList() { return this.ruleList; }
public List<QueryRule> getQueryRuleList() { return this.queryRuleList; }
public String getPropertyName() { return this.propertyName; }
protected class Rule implements Serializable { private static final long serialVersionUID = 1L; private int type; //规则的类型 private String property_name; private Object[] values; private int andOr = AND;
public Rule(int paramInt, String paramString) { this.property_name = paramString; this.type = paramInt; }
public Rule(int paramInt, String paramString, Object[] paramArrayOfObject) { this.property_name = paramString; this.values = paramArrayOfObject; this.type = paramInt; } public Rule setAndOr(int andOr){ this.andOr = andOr; return this; } public int getAndOr(){ return this.andOr; }
public Object[] getValues() { return this.values; }
public int getType() { return this.type; }
public String getPropertyName() { return this.property_name; } }}
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2.5 Order

Order 类主要用于封装排序规则,代码如下:



package com.gupaoedu.vip.orm.framework;
/** * SQL排序组件 */public class Order { private boolean ascending; //升序还是降序 private String propertyName; //哪个字段升序,哪个字段降序 public String toString() { return propertyName + ' ' + (ascending ? "asc" : "desc"); }
/** * Constructor for Order. */ protected Order(String propertyName, boolean ascending) { this.propertyName = propertyName; this.ascending = ascending; }
/** * Ascending order * * @param propertyName * @return Order */ public static Order asc(String propertyName) { return new Order(propertyName, true); }
/** * Descending order * * @param propertyName * @return Order */ public static Order desc(String propertyName) { return new Order(propertyName, false); }}
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因篇幅原因,具体的操作类下一篇继续。


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不只做一个技术者,更要做一个思考者 2021.10.22 加入

畅销书作者,代表作品:《Spring 5核心原理》、《Netty 4核心原理》、《设计模式就该这样学》

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30个类手写Spring核心原理之自定义ORM(上)(6)