Installation and use of db4o
Db4o is an object-oriented database, which can directly store Object storage in the database. The following will provide a detailed introduction to how to install and use db4o, and demonstrate the operations of creating data tables, inserting data, modifying data, querying data, and deleting data.
1. Install db4o:
-Visit the official website of db4o（ http://www.db4o.com/downloads.aspx ）Download the latest version of db4o.
-Choose the appropriate version for download and installation based on your operating system.
-Run the installation program and follow the instructions of the wizard to complete the installation process.
2. Create a data table:
-Introduce the relevant class library of db4o into Java code.
-Create a Java class and define a data model to represent the table structure and fields in the database. For example, create a Student class with id, name, and age fields.
-Instantiate a db4o database object in the code and perform database operations through this object.
3. Insert data:
-Create a Student object and set the values for the id, name, and age fields.
-Save the database object to the database using its store() method. For example: db. store (student);
4. Modify data:
-Use the queryByExample() method of the database object to query the data to be modified. For example: Object Set result=db. queryByExample (new Student (1, 0));
-Modify the values of the fields that need to be modified by traversing the query results.
-Use the store() method of the database object to update the modified object into the database.
5. Query data:
-Use the queryByExample() method of the database object to query the required data. For example: Object Set result=db. queryByExample (new Student (0, "John", 0));
-Traverse the query results to obtain the required data.
6. Delete data:
-Use the queryByExample() method of the database object to query the data that needs to be deleted.
-Use the delete() method of database objects to delete the queried objects.
The following is a complete example code that demonstrates the operations of creating, inserting, modifying, querying, and deleting a Student class:
import com.db4o.*;
public class Main {
public static void main(String[] args) {
//Creating Database Objects
ObjectContainer db = Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), "students.db");
try {
//Create a Student object and insert it into the database
Student student = new Student(1, "John", 20);
db.store(student);
//Modify data
ObjectSet<Student> result = db.queryByExample(new Student(1, "", 0));
if (result.hasNext()) {
Student s = result.next();
s.setAge(21);
db.store(s);
}
//Query data
result = db.queryByExample(new Student(0, "John", 0));
while (result.hasNext()) {
Student s = result.next();
System.out.println("ID: " + s.getId() + ", Name: " + s.getName() + ", Age: " + s.getAge());
}
//Delete data
result = db.queryByExample(new Student(1, "", 0));
while (result.hasNext()) {
Student s = result.next();
db.delete(s);
}
} finally {
//Close database connection
db.close();
}
}
}
class Student {
private int id;
private String name;
private int age;
public Student(int id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
//Omitting getter and setter methods
}
The above is an introduction to the installation and use of db4o, as well as the operations of creating data tables, inserting data, modifying data, querying data, and deleting data. According to the above steps, you can use db4o for object-oriented database operations in your own project.
