Db4o Learning (5)-soda

1. Soda query Graphs

---- A graph data structure

Find all persons whose names are "Lincoln"

 

2. Soda keywords

(1) query keywords

(2) Constraint keywords

 

3. query example

(1) query all

 
DB = db4o. openfile ("Customer. yap"); Query = dB. Query (); query. constrain (customer.Class); List <customer> rsw.query.exe cute ();For(Customer C: RS) {system. Out. println (C. getname ());}
 

 
(2) conditional Query
 

Query query = dB. Query ();Query. constrain (customer.Class); // Class-level constraintsQuery. Descend ("Name"). Constrain ("Customer2"); // Field-level constraintsList <customer> rsw.query.exe cute ();
 

 

(3) Use keywords

 
DB = db4o. openfile ("Customer. yap"); Query = dB. Query (); query. constrain (customer.Class); Query. Descend ("Name"). Constrain ("Customer2"). Not ();List <customer> rsw.query.exe cute ();
 

 
(4) Compound Conditions
 

 
And usage:
 

Query query = dB. Query (); query. constrain (customer.Class);Constraint firstconstr = query. Descend ("Phonenumber"). Constrain ("Phone2"); Query. Descend ("Name"). Constrain ("Customer2"). And (firstconstr );List <customer> rsw.query.exe cute ();
 

 
It is equivalent:
 

 
Query query = dB. Query (); query. constrain (customer.Class); Query. Descend ("Name"). Constrain ("Customer2"); Query. Descend ("Phonenumber"). Constrain ("Phone2"); List <customer> rsw.query.exe cute ();
 

 
Query query = dB. Query ();
 

Or usage: Query. constrain (customer.Class);Constraint firstconstr = query. Descend ("Phonenumber"). Constrain ("Phone3"); Query. Descend ("Name"). Constrain ("Customer2"). Or (firstconstr );List <customer> rsw.query.exe cute ();
 

 
(5) Greater/smaller
 

 
Query query = dB. Query (); query. constrain (person.Class); Query. Descend ("_ Age"). Constrain (80). Greater (); objectset resultappsquery.exe cute ();
 

 

(6) Range Query

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) fuzzy search

 
Query query = dB. Query (); query. constrain (person.Class); Query. Descend ("_ Name"). Constrain ("Ma"). Like ();// Also works with "Ma"Objectset result = query.exe cute ();
 

 

(8) query null values

Query query = dB. Query (); query. constrain (person.Class); Query. Descend ("Age"). Constrain (0 );// Field has been setObjectset resultappsquery.exe cute ();
 

 

(9) sorting results

 
// JavaQuery query = dB. Query (); query. constrain (person.Class); Query. Descend ("_ Name"). Orderascending ();// The list shocould start with the lowestObjectset resultappsquery.exe cute ();