防止@Entity重新创建数据库表-Spring Boot

Question

我对spring boot data jpa有点陌生，据我所知@entity用于表示应用程序中的数据库表，对于这个项目来说，我使用spring-boot 2.2.5.release和h2作为内存数据库。

到目前为止我有这个。

在resources/data.sql内部

CREATE TABLE CURRENCY (
  id INT AUTO_INCREMENT  PRIMARY KEY,
  name VARCHAR(250) NOT NULL,
  code VARCHAR(250) NOT NULL
);

CREATE TABLE EXCHANGE_CURRENCY (
  id INT AUTO_INCREMENT  PRIMARY KEY,
  IdFx1 INT NOT NULL,
  IdFx2 INT NOT NULL,
  equivalent DECIMAL NOT NULL,
  FOREIGN KEY (IdFx1) REFERENCES CURRENCY(id),
  FOREIGN KEY (IdFx2) REFERENCES CURRENCY(id)
);

import javax.persistence.*;

@Entity
@Table(name = "CURRENCY")
public class Currency {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String code;
}

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface CurrencyRepository extends CrudRepository<Currency, Long> {

    @Query("SELECT c FROM CURRENCY WHERE c.code LIKE %:code%")
    List<Currency> findCurrencyByCode(@Param("code") String code);

}

import com.currency.canonical.models.Currency;
import com.currency.canonical.request.ExchangeValueRequest;
import com.currency.canonical.response.ExchangeValueResponse;
import com.currency.dao.CurrencyService;
import com.currency.dao.repository.CurrencyRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.util.List;

@Component
public class CurrencyConversionServiceImpl implements CurrencyConversionService {

    Logger logger = LoggerFactory.getLogger(CurrencyConversionServiceImpl.class);

    @Autowired
    private CurrencyRepository currencyRepository;

    @Override
    public ExchangeValueResponse performCurrencyConversion(ExchangeValueRequest request) {
        final long initialTime = System.currentTimeMillis();

        ExchangeValueResponse objExchangeValueResponse = new ExchangeValueResponse();

        try {
            List<Currency> currencyList = currencyRepository.findCurrencyByCode(request.getMonedaOrigen());
            currencyList.forEach(System.out::println);

        } catch (Exception e) {

        }

        return objExchangeValueResponse;
    }
}

在执行应用程序时，我得到了这个错误

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Initialization of bean failed; nested exception is org.springframework.jdbc.datasource.init.ScriptStatementFailedException: Failed to execute SQL script statement #2 of URL [file:/C:/Users/Usuario/Documents/IdeaProjects/currency-converter/currency-converter-resource/target/classes/data.sql]: CREATE TABLE CURRENCY ( id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(250) NOT NULL, code VARCHAR(250) NOT NULL ); nested exception is org.h2.jdbc.JdbcSQLSyntaxErrorException: Tabla "CURRENCY" ya existe
Table "CURRENCY" already exists; SQL statement:
CREATE TABLE CURRENCY ( id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(250) NOT NULL, code VARCHAR(250) NOT NULL ) [42101-200]

为什么@Entity试图重新创建一个应该只表示的表，有没有一种方法可以禁用它？

Answer 1

这里的问题是文件data.sql的名称，正如spring所建议的，有两个重要的文件可以帮助您控制数据库的创建，它们是

• schema.sql-这个文件顾名思义是创建数据库模式所需的DDL语句。
• data.sql-此文件将保存正确填充初始数据库所需的所有DML语句。

应用程序的问题是DDL是在data.sql文件中指定的，这使spring感到困惑，它试图将DDL视为DML来执行。

此外，我还发现了存储库的另一个问题，因为您使用的是自定义查询@Query（“从货币中选择代码，其中代码像%：code%”）在启动存储库时可能会导致错误，因为java实体名称区分大小写。您可以通过以下方式解决此问题-

a.由于它是一个相似的查询，spring存储库已经支持它，您可以重写类似于-

List<Currency> findByCodeLike(@Param("code") String code);

b.使用JPQL查询，与在代码中所做的相同，只是更改表名，因为JPA实体名区分大小写

@Query("SELECT code FROM Currency WHERE code LIKE %:code%")
List<Currency> findCurrencyByCode(@Param("code") String code);

@Query(value = "SELECT code FROM CURRENCY WHERE code LIKE %:code%", nativeQuery = true)
List<Currency> findCurrencyByCode(@Param("code") String code);