Java的ORM框架有很多，但由于Java语言的限制大部分都不够优雅也不够简单，所以作者只能另辟蹊径造轮子了。照旧先看示例代码了解个大概，然后再解释实现原理。
一、ORM示例 1. Insert public CompletableFuture<Void> insert() { var obj = new sys.entities.Demo("MyName"); //构造参数为主键 obj.Age = 100; //设置实体属性的值 return obj.saveAsync(); } 2. Update更新单个实体（必须具备主键）
public CompletableFuture<Void> update(sys.entities.Demo obj) { obj.Age = 200; return obj.saveAsync(); }根据条件更新（必须指定条件以防误操作）
public CompletableFuture<?> update() { var cmd = new SqlUpdateCommand<sys.entities.Demo>(); cmd.update(e -> e.City = "Wuxi"); //更新字段 cmd.update(e -> e.Age = e.Age + 1); //更新累加字段 cmd.where(e -> e.Name == "Johne"); //更新的条件 var outs = cmd.output(e -> e.Age); //更新的同时返回指定字段 return cmd.execAsync().thenApply(rows -> { System.out.println("更新记录数: " + rows); System.out.println("返回的值: " + outs.get(0)); return "Done."; }); } 3. Delete删除单个实体（必须具备主键）
public CompletableFuture<Void> update(sys.entities.Demo obj) { obj.markDeleted(); //先标记为删除状态 return obj.saveAsync(); //再调用保存方法 }根据条件删除（必须指定条件以防误操作）
public CompletableFuture<?> delete() { var cmd = new SqlDeleteCommand<sys.entities.Demo>(); cmd.where(e -> e.Age < 0 || e.Age > 200); return cmd.execAsync(); } 4. Transaction由于作者讨厌隐式事务，所以事务命令必须显式指定。
public CompletableFuture<?> transaction() { var obj1 = new sys.entities.Demo("Demo1"); obj1.Age = 11; var obj2 = new sys.entities.Demo("Demo2"); obj2.Age = 22; return DataStore.DemoDB.beginTransaction().thenCompose(txn -> { //开始事务 return obj1.saveAsync(txn) //事务保存obj1 .thenCompose(r -> obj2.saveAsync(txn)) //事务保存obj2 .thenCompose(r -> txn.commitAsync()); //递交事务 }).thenApply(r -> "Done"); } 5. Sql查询Where条件
public CompletableFuture<?> query(String key) { var q = new SqlQuery<sys.entities.Demo>(); q.where(e -> e.Age > 10 && e.Age < 80); if (key != null) q.andWhere(e -> e.Name.contains(key)); //拼接条件 return q.toListAsync(); //返回List<sys.entities.Demo> }分页查询
public CompletableFuture<?> query(int pageSize, int pageIndex) { var q = new SqlQuery<sys.entities.Demo>(); return q.skip(pageSize * pageIndex) .take(pageSize) .toListAsync(); }结果映射至匿名类
public CompletableFuture<?> query() { var q = new SqlQuery<sys.entities.Demo>(); return q.toListAsync(e -> new Object() { //返回List<匿名类> public final String Name = e.Name; //匿名类属性 = 实体属性表达式 public final int Age = e.Age + 10; public final String Father = e.Parent.Name; }).thenApply(appbox.data.JsonResult::new); }结果映射至继承的匿名类
public CompletableFuture<?> query() { var q = new SqlQuery<sys.entities.Demo>(); q.where(e -> e.Parent.Name == "Rick"); return q.toListAsync(e -> new sys.entities.Demo() { //返回List<? extens Demo> public final String Father = e.Parent.Name; }); }结果映射至树状结构列表
public CompletableFuture<?> tree() { var q = new SqlQuery<sys.entities.Demo>(); q.where(t -> t.Name == "Rick"); return q.toTreeAsync(t -> t.Childs); //参数指向EntitySet(一对多成员） }EntityRef(一对一引用的实体成员)自动Join
public CompletableFuture<?> query() { var q = new SqlQuery<sys.entities.Customer>(); q.where(cus -> cus.City.Name == "Wuxi"); return q.toListAsync(); } 生成的Sql: Select t.* From "Customer" t Left Join "City" j1 On j1."Code"=t."CityCode"手工指定Join
public CompletableFuture<?> join() { var q = new SqlQuery<sys.entities.Customer>(); var j = new SqlQueryJoin<sys.entities.City>(); q.leftJoin(j, (cus, city) -> cus.CityCode == city.Code); q.where(j, (cus, city) -> city.Name == "Wuxi"); return q.toListAsync(); }子查询
public CompletableFuture<?> subQuery() { var sq = new SqlQuery<sys.entities.Demo>(); sq.where(s -> s.ParentName == "Rick"); var q = new SqlQuery<sys.entities.Demo>(); q.where(t -> DbFunc.in(t.Name, sq.toSubQuery(s -> s.Name))); return q.toListAsync(); }GroupBy
public CompletableFuture<?> groupBy() { var q = new SqlQuery<sys.entities.Demo>(); q.groupBy(t -> t.ParentName) //多个可重复 .having(t -> DbFunc.sum(t.Age) > 10); return q.toListAsync(t -> new Object() { public final String group = t.ParentName == null ? "可怜的孩子" : t.ParentName; public final int totals = DbFunc.sum(t.Age); }).thenApply(appbox.data.JsonResult::new); } 二、实现原理