"Welcome To Ashok IT"				
			                     "Spring Boot and MicroServices"
                                               Topic : Spring Data JPA - Generators
                                              	 Date  : 10/10/2024
                                                  (Session - 42)                  
_____________________________________________________________________________________________________________________________
Today Session
==============

Generators
==========
* Basically in application development will have multiple database tables.

* Each Database table will have mandatorly primary key column which is combination of two constraints i.e.,Unique + not null    constraint.
 
* While inserting records into database table, If end user supplied primary key value might have chance for entering            duplicate value for primary key column.

* To Overcome this problem ORM Framework provided the generators concept.

* Generators are used in application for generating the Primary key column value based on some mechanism supported by           database vendor.

* When we use generators in application before saving record primary key value will be generated with in application then  
  record will be inserted into table along with primary key.

* ORM Will support's the four types of Generators are as below 

       1) AUTO

       2) SEQUENCE

       3) IDENTITY

       4) TABLE

* We can use the following annotation @GeneratedValue helps for generating value for primary key based on strategy defined.

* @GeneratedValue annotation should be defined on top of primary key column field in entity class.

************************
1) GenerationType.AUTO
************************
>> This is the default generation type strategy for generating the primary key value of Database column.

>> We can define the auto strategy on top of the primary key field in Entity Class with below annotation
       
       @Id
       @GeneratedValue(strategy=GenerationType.AUTO)
       private Integer productId;

>> If we are using Oracle database internally Hibernate will create sequence database object with the name of                    hibernate_sequence.
       
   Ex:  create sequence hibernate_sequence starts with 1 and increment by 1;  >>>> SpringBoot 2.7.X version

        create sequence shopping_customer_seq start with 1 increment by 50 >>>> Spring Boot 3.X Table specific Sequence.

        create sequence mahesh_customers_seq start with 1 increment by 50  >>>>>> Spring Boot 3.X Table Specific Sequence.

>> Before inserting the record into database table Hibernate will select value for hibernate_sequence/table specific sequence    and insert into primary key column value.

     Ex:  select hibernate_sequence.nextval from dual;  >>>>>>> SpringBoot 2.7.x Version

          select shopping_customers_seq.nextval from dual; >>>>>>> SpringBoot 3.x Version

          insert into shopping_customers(?,?,?,?,?);

>> If we are using MYSQL database internally Hibernate Will create table per entity class 
   because MySQL doesn't supports the sequences concept and inorder to generate the primary key column value in MYSQL will      have auto increment facility.

       create table hibernate_sequence(
          next_val bigint;
       );

       insert into hibernate_sequence values(1);

NOTE
====
Hibernate: 
    create table shopping_customers (
        customer_id integer not null,
        contact_no varchar(255),
        email varchar(255),
        location varchar(255),
        name varchar(255),
        primary key (customer_id)
    ) engine=InnoDB

Hibernate: 
    create table shopping_customers_seq (
        next_val bigint
    ) engine=InnoDB

Hibernate: 
    insert into shopping_customers_seq values ( 1 )

Hibernate: 
    select
        next_val as id_val 
    from
        shopping_customers_seq for update
Hibernate: 
    update
        shopping_customers_seq 
    set
        next_val= ? 
    where
        next_val=?
Hibernate: 
    insert 
    into
        shopping_customers
        (contact_no, email, location, name, customer_id) 
    values
        (?, ?, ?, ?, ?)

>> Before inserting the record into database table Hibernate will select value for hibernate_sequence table and insert into      primary column value.

Example Application
===================

Customer.java
=============
package com.ashokit.enities;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="mahesh_cutomers")
public class Customer {
	
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Integer customerId;
	
	private String customerName;
	
	private String customerLocation;

	public Integer getCustomerId() {
		return customerId;
	}

	public void setCustomerId(Integer customerId) {
		this.customerId = customerId;
	}

	public String getCustomerName() {
		return customerName;
	}

	public void setCustomerName(String customerName) {
		this.customerName = customerName;
	}

	public String getCustomerLocation() {
		return customerLocation;
	}

	public void setCustomerLocation(String customerLocation) {
		this.customerLocation = customerLocation;
	}

	@Override
	public String toString() {
		return "Customer [customerId=" + customerId + ", customerName=" + customerName + ", customerLocation="
				+ customerLocation + "]";
	}
	
}


CustomerDao.java
================
package com.ashokit.dao;

import org.springframework.data.repository.CrudRepository;

import com.ashokit.enities.Customer;

public interface CustomerDao extends CrudRepository<Customer, Integer> {

}


Application.java
================
package com.ashokit;

import java.util.Arrays;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import com.ashokit.dao.CustomerDao;
import com.ashokit.enities.Customer;

@SpringBootApplication
public class Application implements CommandLineRunner{
	
	@Autowired
	private CustomerDao customerDao;

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}
	
	@Override
	public void run(String... args) throws Exception {
		
		//inserting the record for an customer
		Customer c = new Customer();
		c.setCustomerName("Mahesh");
		c.setCustomerLocation("Hyderabad");
		
		Customer c2 = new Customer();
		c2.setCustomerName("Ashok");
		c2.setCustomerLocation("Bangalore");
		
		Iterable<Customer> savedCustomers = customerDao.saveAll(Arrays.asList(c,c2));
		savedCustomers.forEach(cust -> System.out.println(cust));
	}
}


application.properties
======================
#configuring the Database properties
spring.datasource.driver-class-name=oracle.jdbc.OracleDriver
spring.datasource.url=jdbc:oracle:thin:@localhost:1521:xe
spring.datasource.username=system
spring.datasource.password=manager

#Hibernate Configuration
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

********************************
Problem With hibernate_sequence 
********************************
  ShoppingCustomers  >>>>>>  shopping_customers(DBTable) >>>>>> hibernate_sequence >>>>> Oracle Database

  ShoppingEmployee   >>>>>>  shopping_employees(DBTable) >>>>>> hibernate_sequence >>>>> Oracle Database

  1) You Performed 5 insertions into shopping_customers DB Table  >>>>>> CustomerIds(1,2,3,4,5)
          
  2) You Performed 5 inserstion into shopping_employees DB Table >>>>>> employeeids(6,7,8,9,10)

  3) You Performed 5 insertions into shopping_customers DB Table >>>>>> customerIds(11,12,13,14,15)

  4) You Performed 5 insertions into shopping_employees DB Table >>>>>> employeeids(16,17,18,19,20)

  5) Viewing the data for shopping_customers :1,2,3,4,5,11,12,13,14,15

  6) Viewing the data for shopping_employees :6,7,8,9,10,15,16,17,18,19,20

  If you observe the data for above two tables primary key column values are not in sync i.e.,Data Inconsistency.

  Inorder to overcome this problem we need to create independent sequence per database table.

        shopping_customers >>>>> shopping_customers_sequence  >>>> GenerationType.SEQUENCE

        shopping_employees >>>>> shopping_employees_sequence  >>>> GenerationType.SEQUENCE

***************************
2) GenerationType.SEQUENCE
***************************
* In Order to overcome the problem of hibernate_sequence we need to came for this type of strategy with respective to           Hibernate 5.x version.

* From Hibernate 6.x version onwards we know that table specific sequence generation is happening in that default sequence      initial value as 1 and increment by 50.

* In this strategy Hibernate provided the facility to generate our own custom sequence name and we can customize the sequence   initial value and increment value per table automatically with help of the following annotation i.e.,@SequenceGenerator.

Example
=======
      @Id
      @GeneratedValue(
          strategy = GenerationType.SEQUENCE,
          generator = "customer_seq"
      )
      @SequenceGenerator(
          name = "customer_seq",
          sequenceName ="shopping_customers_seq",
          initialValue = 1000,
          allocationSize = 1
      )
      private Integer customerId;

* This type of generator is used to generate primary key values and uses a database sequence to generate unique values.

* Inorder to generate primary key column we required additional select statement along with insert statement.

* @SequenceGenerator annotation will takecare of creating sequence with name as "shopping_customers_seq" and defined the        name of the generator i.e.,customer_seq and required allocation size of the sequence for incrementation.

Example Application
===================

Product.java
============
package com.ashokit.enities;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

@Entity
@Table(name="mahesh_products")
public class Product {
	
	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "product_seq")
	@SequenceGenerator(name = "product_seq",
	                   sequenceName = "mahesh_products_seq",
	                   initialValue = 1000,
	                   allocationSize = 1) 
	private Integer productId;
	
	private String productName;
	
	private float productPrice;

	public Integer getProductId() {
		return productId;
	}

	public void setProductId(Integer productId) {
		this.productId = productId;
	}

	public String getProductName() {
		return productName;
	}

	public void setProductName(String productName) {
		this.productName = productName;
	}

	public float getProductPrice() {
		return productPrice;
	}

	public void setProductPrice(float productPrice) {
		this.productPrice = productPrice;
	}

	@Override
	public String toString() {
		return "Product [productId=" + productId + ", productName=" + productName + ", productPrice=" + productPrice
				+ "]";
	}
}

ProductDao.java
===============
public interface ProductDao extends CrudRepoistory<Product,Integer>{


}


Vehicle.java
============
package com.ashokit.enities;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

@Entity
@Table(name = "mahesh_vehicles")
public class Vehicle {

	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "vehicle_seq")
	@SequenceGenerator(name = "vehicle_seq", 
	                   sequenceName = "mahesh_vehicles_seq", 
	                   initialValue = 1,
	                   allocationSize = 1)
	private Integer vehicleId;

	private String vehicleName;

	private float vehicleCost;

	public Integer getVehicleId() {
		return vehicleId;
	}

	public void setVehicleId(Integer vehicleId) {
		this.vehicleId = vehicleId;
	}

	public String getVehicleName() {
		return vehicleName;
	}

	public void setVehicleName(String vehicleName) {
		this.vehicleName = vehicleName;
	}

	public float getVehicleCost() {
		return vehicleCost;
	}

	public void setVehicleCost(float vehicleCost) {
		this.vehicleCost = vehicleCost;
	}

	@Override
	public String toString() {
		return "Vehicle [vehicleId=" + vehicleId + ", vehicleName=" + vehicleName + ", vehicleCost=" + vehicleCost
				+ "]";
	}

}

VehicleDao.java
===============
public interface VehicleDao extends CrudRepoistory<Vehicle,Integer>{


}


Application.java
================
package com.ashokit;

import java.util.Arrays;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import com.ashokit.dao.BikeDao;
import com.ashokit.dao.CustomerDao;
import com.ashokit.dao.EmployeeDao;
import com.ashokit.dao.ProductDao;
import com.ashokit.dao.VehicleDao;
import com.ashokit.enities.Bike;
import com.ashokit.enities.Employee;
import com.ashokit.enities.Product;
import com.ashokit.enities.Vehicle;

@SpringBootApplication
public class Application implements CommandLineRunner{
	
	
	@Autowired
	private ProductDao productDao;
	
	@Autowired
	private VehicleDao vehicleDao;

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}
	
	@Override
	public void run(String... args) throws Exception {
				
		Product p = new Product();
		p.setProductName("Laptop");
		p.setProductPrice(50000.00f);
		
		Product p1 =new Product();
		p1.setProductName("Mobilephone");
		p1.setProductPrice(10000.00f);
		
		Iterable<Product> savedProducts = productDao.saveAll(Arrays.asList(p,p1));
		savedProducts.forEach(prod -> System.out.println(prod));   
		
		System.out.println("*****************************************************************");
		
		Vehicle  v1 = new Vehicle();
		v1.setVehicleName("Tata");
		v1.setVehicleCost(50000.00f);
		
		Vehicle v2 = new Vehicle();
		v2.setVehicleName("Hyundai");
		v2.setVehicleCost(60000.00f);
		
		Iterable<Vehicle> savedVehicles = vehicleDao.saveAll(Arrays.asList(v1,v2));
		savedVehicles.forEach(veh  -> System.out.println(veh));
				
	}
}

NOTE
====
 Observe the Output of the Spring Boot Application Console.