Creating a JPA Repository

In the previous section, we have created a table in-memory database and saw that all the data is populated correctly. In this section, we will create a repository that returns the response for the service.

Step 1: Create an interface with the name ExchangeValueRepository and extends the JpaRepository class. We have to pass two parameters: type of the entity that it manages and the type of the Id field.

public interface ExchangeValueRepository extends JpaRepository<ExchangeValue, Long>

Step 2: Open CurrencyExchageController.java file and autowired the ExchageValueRepository.

@Autowired
private ExchangeValueRepository repository;

Step 3: Create a query method in the ExcahngeValueRepository.java file.

In the above statement, ExchangeValue is the expected response. There are two columns that we have to find are from and to.

If we want to find data on the basis of single column, we can pass a column name. For example:

ExcahngeValueRepository.java

package com.javatpoint.microservices.currencyexchangeservice;
import org.springframework.data.jpa.repository.JpaRepository;
public interface ExchangeValueRepository extends JpaRepository<ExchangeValue, Long>
{
//creating query method
ExchangeValue findByFromAndTo(String from, String to);
}

Step 4: In the CurrencyExchangeController.java use the following statement:

Instead of using the following statement:

ExchangeValue exchangeValue=new ExchangeValue(1000L, from, to, BigDecimal.valueOf(65));

CurrencyExchangeController.java

package com.javatpoint.microservices.currencyexchangeservice;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.core.env.Environment;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
@RestController 
public class CurrencyExchangeController 
{
@Autowired
private Environment environment;
@Autowired
private ExchangeValueRepository repository;
@GetMapping("/currency-exchange/from/{from}/to/{to}")		//where {from} and {to} are path variable
public ExchangeValue retrieveExchangeValue(@PathVariable String from, @PathVariable String to)   //from map to USD and to map to INR
{		
ExchangeValue exchangeValue = repository.findByFromAndTo(from, to);
//setting the port
exchangeValue.setPort(Integer.parseInt(environment.getProperty("local.server.port")));
return exchangeValue;
}
}

Step 5: Restart the application to pick up the changes. Open the browser and type the URI http://localhost:8000/currency-exchange/from/USD/to/INR. It returns the following response:

We can also try a different conversion by changing the currency USD to EUR in the URI.

http://localhost:8000/currency-exchange/from/EUR/to/INR.

It returns the following response:

In this above response, we are retrieving the values from the database.

When we pass the currency in the URI (EUR/to/INR), the query gets fired to the database. To see which query gets fired, we can see the query in the log.

Hibernate: select exchangeva0_.id as id1_0_, exchangeva0_.conversion_multiple as conversi2_0_, exchangeva0_.currency_from as currency3_0_, exchangeva0_.port as port4_0_, exchangeva0_.currency_to as currency5_0_ from exchange_value exchangeva0_ where exchangeva0_.currency_from=? and exchangeva0_.currency_to=?

Click here to download currency-conversion-service

Next TopicSetting up Currency Conversion Microservice

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