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📜  创建一个JPA存储库

📅  最后修改于: 2021-01-11 02:24:05             🧑  作者: Mango

创建一个JPA存储库

在上一节中，我们创建了一个表内存数据库，并看到正确填充了所有数据。在本节中，我们将创建一个存储库，该存储库返回服务的响应。

步骤1：创建一个名称为ExchangeValueRepository的接口，并扩展JpaRepository类。我们必须传递两个参数：它管理的实体的类型和Id字段的类型。

public interface ExchangeValueRepository extends JpaRepository

第2步：打开CurrencyExchageController.java文件并自动连接ExchageValueRepository 。

@Autowired
private ExchangeValueRepository repository;

步骤3：在ExcahngeValueRepository.java文件中创建查询方法。

ExchangeValue findByFromAndTo(String from, String to);

在上面的语句中， ExchangeValue是预期的响应。我们必须找到from和to两列。

如果要基于单列查找数据，则可以传递列名。例如：

ExchangeValue findByFrom (String from);

ExcahngeValueRepository.java

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

步骤4：在CurrencyExchangeController.java中，使用以下语句：

ExchangeValue exchangeValue=repository.findByFromAndTo(from,to);

而不是使用以下语句：

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;
}
}

步骤5：重新启动应用程序以获取更改。打开浏览器，然后输入URI http：// localhost：8000 / currency-exchange / from / USD / to / INR 。它返回以下响应：

我们还可以尝试通过将URI中的货币USD更改为EUR来进行其他转换。

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

它返回以下响应：

在以上响应中，我们正在从数据库中检索值。

当我们在URI(EUR / to / INR)中传递货币时，查询将触发到数据库。要查看触发了哪个查询，我们可以在日志中查看该查询。

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=?