Using Java to operate db4o
Db4o is an object-oriented Database management system, which can directly store and retrieve Java objects. Using Java to operate db4o includes importing Maven dependencies, establishing database connections, creating/modifying/querying/deleting objects.
Firstly, add the following dependencies to the Maven project:
<dependency>
<groupId>com.db4o</groupId>
<artifactId>db4o-full-java5</artifactId>
<version>8.1-SNAPSHOT-2710243267</version>
</dependency>
Next, we will gradually introduce how to use Java code to implement data insertion, modification, query, and deletion.
1. Establish database connection:
import com.db4o.*;
import com.db4o.query.*;
public class Db4oExample {
private static ObjectContainer db;
public static void main(String[] args) {
db = Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), "database.db");
// perform operations on db
db.close();
}
}
2. Create objects:
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
3. Data insertion:
Person person = new Person("Alice", 25);
db.store(person);
4. Data Query:
ObjectSet<Person> result = db.query(Person.class);
while (result.hasNext()) {
Person person = result.next();
System.out.println(person.getName() + ", " + person.getAge());
}
5. Data modification and deletion:
ObjectSet<Person> result = db.query(new Predicate<Person>() {
public boolean match(Person person) {
return person.getName().equals("Alice");
}
});
while (result.hasNext()) {
Person person = result.next();
Person. setAge (30)// Modify data
Db. store (person)// Update Object
Db. delete (person)// delete object
}
Complete code example:
import com.db4o.*;
import com.db4o.query.*;
public class Db4oExample {
private static ObjectContainer db;
public static void main(String[] args) {
db = Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), "database.db");
// Insert Example
Person alice = new Person("Alice", 25);
db.store(alice);
// Update and Delete Example
ObjectSet<Person> result = db.query(new Predicate<Person>() {
public boolean match(Person person) {
return person.getName().equals("Alice");
}
});
while (result.hasNext()) {
Person person = result.next();
Person. setAge (30)// Modify data
Db. store (person)// Update Object
Db. delete (person)// delete object
}
// Query Example
ObjectSet<Person> result = db.query(Person.class);
while (result.hasNext()) {
Person person = result.next();
System.out.println(person.getName() + ", " + person.getAge());
}
db.close();
}
}
The above example code demonstrates how to use Java operations db4o for data insertion, modification, query, and deletion. Please make modifications and extensions according to actual needs.
