May 17, 2021 Hibernate
JDBC stands for Java Database Connectivity, a Java program that provides a set of Java APIs to access the relationship database. These Java APIs enable Java applications to execute SQL statements and interact with any SQL-compliant database.
JDBC provides a flexible framework for writing stand-alone applications that manipulate databases that can run on different platforms without modification and interact with different DBMS.
| Advantages of JDBC | The disadvantages of JDBC |
|---|---|
| Clean and tidy SQL handling | The use of large projects is complex |
| Good performance under big data | It's a big programming cost |
| Very good for small applications | There is no encapsulation |
| Easy-to-learn simple grammar | The concept of MVC is difficult to implement |
| The query needs to specify DBMS |
When we work in an object-oriented system, there is a mismatch between the object model and the relationship database. R DBMSs store data as tables, but object-oriented languages such as Java or C# represent an object association diagram. Consider the following Java classes with construction and public methods:
public class Employee {
private int id;
private String first_name;
private String last_name;
private int salary;
public Employee() {}
public Employee(String fname, String lname, int salary) {
this.first_name = fname;
this.last_name = lname;
this.salary = salary;
}
public int getId() {
return id;
}
public String getFirstName() {
return first_name;
}
public String getLastName() {
return last_name;
}
public int getSalary() {
return salary;
}
}Objects considered above need to be stored and indexed in the following RDBMS tables:
create table EMPLOYEE (
id INT NOT NULL auto_increment,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary INT default NULL,
PRIMARY KEY (id)
);First question, what if we need to modify the design of the database after we have developed a few pages of code or applications?
Second, we face the following five mismatches when loading and storing objects in a relationship database.
| Does not match | Describe |
|---|---|
| Granularity | Sometimes you will have an object model with more classes than the number of tables associated in the database |
| Inherited | RDBMSs do not define any inheritance that is inherent in object-oriented programming languages |
| Identity | RDBMS clearly defines the concept of 'sameness': primary keys. However, Java defines both object-judgment (a-b) and object value-judgment (a.equals(b)) |
| Association | Object-oriented programming languages use object references to represent associations, while an RDBMS uses foreign keys to represent object associations |
| Navigation | Objects are accessed in Java and in RDBMS in exactly the same way |
O bject-R Elational M Apping (ORM) is the solution to all of these mismatches.
ORM, which represents Object-Relational Mapping (ORM), is a technology that makes it easy to transform data in relational databases and object-oriented programming languages such as Java, C, and so on. An ORM system has the following advantages over a normal JDBC.
| Serial number | Advantages |
|---|---|
| 1 | Use business code to access objects instead of tables in the database |
| 2 | Hide the details of SQL queries from object-oriented logic |
| 3 | JDBC-based 'under thehood' |
| 4 | There is no need to work with database implementations |
| 5 | Entities are business-based concepts, not database structures |
| 6 | Automatic generation of transaction management and keys |
| 7 | Rapid development of applications |
An ORM solution consists of four entities:
| Serial number | Advantages |
|---|---|
| 1 | An API to implement basic CRUD operations on objects of persistent classes |
| 2 | A language or API to specify queries that refer to classes and properties |
| 3 | A configurable service is used to specify mapping metadata |
| 4 | A technology and transaction object interaction to perform dirty checking, lazy association fetching, and other optimized functions |
There are several persistent frameworks and ORM options in Java. A persistent framework is the service that ORM stores and indexes objects to the relationship database.