DB4O之SODA查询

写在前面，详细的db4o中英文指南参见满江红：http://wiki.redsaga.com/confluence/pages/viewpage.action?pageId=2137

1.SODA Query Graphs 
自：http://www.cnblogs.com/cxccbv/archive/2009/02/19/1394380.html
   ----a graph data structure


查找所有name为“Lincoln”的Person


2.SODA关键字

（1）查询关键字
 

（2）约束关键字
 

3.查询示例

（1）查询全部

  

db = Db4o.openFile("customer.yap"); 
Query query = db.query(); query.constrain(Customer.class); List<Customer> rs = query.execute(); 
for(Customer c:rs){ 
    System.out.println(c.getName()); 
} 

  

（2）条件查询 

 

 

Query query=db.query();
query.constrain(Customer.class);//类级别的约束 
query.descend("name").constrain("customer2");//字段级别的约束 List<Customer> rs=query.execute();

 

  
（3）使用关键字

 

 

db = Db4o.openFile("customer.yap"); 
Query query=db.query(); 
query.constrain(Customer.class); 
query.descend("name").constrain("customer2").not(); 
List<Customer> rs=query.execute(); 

 

 
（4）复合条件 

 

 

and的用法：

Query query=db.query(); 
query.constrain(Customer.class); 
Constraint firstConstr=query.descend("phoneNumber").constrain("phone2"); 
query.descend("name").constrain("customer2").and(firstConstr); List<Customer> rs=query.execute(); 

 

  
等价于： 

 

 

 

Query query=db.query(); 
query.constrain(Customer.class); 
query.descend("name").constrain("customer2"); 
query.descend("phoneNumber").constrain("phone2"); List<Customer> rs=query.execute(); 
Query query=db.query(); 

  

 
or的用法：

 

query.constrain(Customer.class); 
Constraint firstConstr=query.descend("phoneNumber").constrain("phone3"); 
query.descend("name").constrain("customer2").or(firstConstr); List<Customer> rs=query.execute(); 

 

 

（5）greater/smaller

 

 

Query query=db.query(); 
query.constrain(Person.class); 
query.descend("_age").constrain(80).greater(); 
ObjectSet result=query.execute(); 

 

（6）范围查询 

 

 

 

 

Query query=db.query(); 
query.constrain(Person.class); 
Constraint firstConstr = query.descend("_age").constrain(60).greater(); 
query.descend("_age").constrain(80).smaller().and(firstConstr);

 

（7）模糊查询

Query query=db.query(); 
query.constrain(Person.class); 
query.descend("_name").constrain("Ma").like(); // also works with "ma" ObjectSet result= query.execute(); 

 

 

 

 

 


（8）查询空值

 

Query query=db.query(); 
query.constrain(Person.class); 
query.descend("age").constrain(0); // field has been set ObjectSet result=query.execute(); 

 

  

（9）结果排序

 

JAVA Query query=db.query(); 
query.constrain(Person.class); 
query.descend("_name").orderAscending(); // the list should start with the lowest ObjectSet result=query.execute();