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1 package com.db4o.f1.chapter1;
2
3 import com.db4o.Db4o;
4 import com.db4o.ObjectContainer;
5 import com.db4o.ObjectSet;
6 import com.db4o.f1.Util;
7 import com.db4o.query.Constraint;
8 import com.db4o.query.Query;
9
10
11 public class QueryExample extends Util {
12 public static void main(String  [] args) {
13 ObjectContainer db=Db4o.openFile(Util.YAPFILENAME);
14 try {
15 storeFirstPilot(db);
16 storeSecondPilot(db);
17 retrieveAllPilots(db);
18 retrievePilotByName(db);
19 retrievePilotByExactPoints(db);
20 retrieveByNegation(db);
21 retrieveByConjunction(db);
22 retrieveByDisjunction(db);
23 retrieveByComparison(db);
24 retrieveByDefaultFieldValue(db);
25 retrieveSorted(db);
26 clearDatabase(db);
27 }
28 finally {
29 db.close();
30 }
31 }
32
33 public static void storeFirstPilot(ObjectContainer db) {
34 Pilot pilot1=new Pilot("Michael Schumacher",100);
35 db.set(pilot1);
36 System.out.println("Stored "+pilot1);
37 }
38
39 public static void storeSecondPilot(ObjectContainer db) {
40 Pilot pilot2=new Pilot("Rubens Barrichello",99);
41 db.set(pilot2);
42 System.out.println("Stored "+pilot2);
43 }
44
45 public static void retrieveAllPilots(ObjectContainer db) {
46 Query query=db.query();
47 query.constrain(Pilot.class);
48 ObjectSet result=query.execute();
49 listResult(result);
50 }
51
52 public static void retrievePilotByName(ObjectContainer db) {
53 Query query=db.query();
54 query.constrain(Pilot.class);
55 query.descend("name").constrain("Michael Schumacher");
56 ObjectSet result=query.execute();
57 listResult(result);
58 }
59
60 public static void retrievePilotByExactPoints(
61 ObjectContainer db) {
62 Query query=db.query();
63 query.constrain(Pilot.class);
64 query.descend("points").constrain(new Integer (100));
65 ObjectSet result=query.execute();
66 listResult(result);
67 }
68
69 public static void retrieveByNegation(ObjectContainer db) {
70 Query query=db.query();
71 query.constrain(Pilot.class);
72 query.descend("name").constrain("Michael Schumacher").not();
73 ObjectSet result=query.execute();
74 listResult(result);
75 }
76
77 public static void retrieveByConjunction(ObjectContainer db) {
78 Query query=db.query();
79 query.constrain(Pilot.class);
80 Constraint constr=query.descend("name")
81 .constrain("Michael Schumacher");
82 query.descend("points")
83 .constrain(new Integer (99)).and(constr);
84 ObjectSet result=query.execute();
85 listResult(result);
86 }
87
88 public static void retrieveByDisjunction(ObjectContainer db) {
89 Query query=db.query();
90 query.constrain(Pilot.class);
91 Constraint constr=query.descend("name")
92 .constrain("Michael Schumacher");
93 query.descend("points")
94 .constrain(new Integer (99)).or(constr);
95 ObjectSet result=query.execute();
96 listResult(result);
97 }
98
99 public static void retrieveByComparison(ObjectContainer db) {
100 Query query=db.query();
101 query.constrain(Pilot.class);
102 query.descend("points")
103 .constrain(new Integer (99)).greater();
104 ObjectSet result=query.execute();
105 listResult(result);
106 }
107
108 public static void retrieveByDefaultFieldValue(
109 ObjectContainer db) {
110 Pilot somebody=new Pilot("Somebody else",0);
111 db.set(somebody);
112 Query query=db.query();
113 query.constrain(Pilot.class);
114 query.descend("points").constrain(new Integer (0));
115 ObjectSet result=query.execute();
116 listResult(result);
117 db.delete(somebody);
118 }
119
120 public static void retrieveSorted(ObjectContainer db) {
121 Query query=db.query();
122 query.constrain(Pilot.class);
123 query.descend("name").orderAscending();
124 ObjectSet result=query.execute();
125 listResult(result);
126 query.descend("name").orderDescending();
127 result=query.execute();
128 listResult(result);
129 }
130
131 public static void clearDatabase(ObjectContainer db) {
132 ObjectSet result=db.get(Pilot.class);
133 while(result.hasNext()) {
134 db.delete(result.next());
135 }
136 }
137 }
138 |
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Java API By Example, From Geeks To Geeks.