英文:

why the entity can't map the columns table?

问题

我有一个名为"countries"的MySQL表，结构如下：

| id | name | name2 | code | area | currency | language | population |

| .. | .. | ... | ...| ....| ... | ... | ... |

有一个实体叫做"customCountry"：

```java
@Entity
@Table(name="countries")
public class customCountry {
    @Id
    @Column(name = "id", table ="countries")
    private Long id;

    @Column(name = "code", table ="countries")
    private Long code;

    @Column(name = "language", table ="countries")
    private String language;

    // 构造函数 + getter/setter
}

我有这个Repository：

@Repository
public interface customCountryRepository extends JpaRepository<customCountry, Long>{

    List<customCountry> findAll();
}

以及这个Service类：

@Service
@ComponentScan(basePackages="repository")
public class countriesService {

    @Autowired
    customCountryRepository customcountry_repo;
    
    public List<customCountry> loadcustomcountries() {
        List<customCountry> validcustomcountries = customcountry_repo.findAll();
        System.out.println("size: " + validcustomcountries.size());
        return validcustomcountries;
    }
}

问题是，当我在控制器中调用这个Service方法时，我发现大小为0，但我不知道为什么，我认为我已经很好地管理了属性和列之间的映射。谢谢

<details>
<summary>英文:</summary>

i have a mysql table &quot;countries&quot; as follow 

| id | name | name2 | code | area | currency | language | population |

| .. | .. | ... | ...| ....| ... | ... | ... |

this entity "customCountry":

@Entity
@Table(name="countries")
public class customCountry {
@Id
@Column(name = "id",table ="countries")
private Long id;

@Column(name = "code",table ="countries")
 private Long code;

@Column(name = "language",table ="countries")
 private String language;

//constructors + getters/setters
}

i have this repository :

@Repository
public interface customCountryRepository extends JpaRepository<customCountry,Long>{

List<customCountry> findAll();

}

and this service class :

@Service
@ComponentScan(basePackages="repository")
public class countriesService {

@Autowired
customCountryRepository customcountry_repo;

public List<customCountry> loadcustomcountries()
{
	List<customCountry> validcustomcountries = customcountry_repo.findAll();
	System.out.println("size: "+validcustomcountries.size());
	return validcustomcountries;
}

}

the problem is that when i called this service method in my controller , i find out that the size = 0 , but i don't see why , i think that i well managed the mapping between attributes and columns though .
thank you

</details>


# 答案1
**得分**: 0

你可以从仓库类中移除 **`List&lt;customCountry&gt; findAll();`**。

因为你已经扩展了 **`JpaRepository&lt;customCountry,Long&gt;`**，它已经有了这个方法。

尽管你在仓库中提供了这个方法，但没有实现它。
这可能会导致问题。

试试移除它看看。

<details>
<summary>英文:</summary>

You can remove  **`List&lt;customCountry&gt; findAll();`** from repository class.

As you had already extended **`JpaRepository&lt;customCountry,Long&gt;`**, it&#39;s have this method.

As you are providing that method in repository but not implementation of it.
That is causing an issue.

Just try by removing it.

</details>