找不到能够从 [java.lang.String] 类型转换为 [@Autowired @ManyToOne @JoinColumn com.papertrue.country.Country] 类型的转换器

Question

So I'm pretty new to JPA and I'm stuck while mapping an object into another object. Here's my User Entity:

package com.papertrue.user;

import com.papertrue.country.Country;
import com.papertrue.currency.Currency;

@Entity
@ConfigurationProperties("user")
@Table(name = "users")
public class User {

    @Id
    @Column(name = "id")
    private String userId;

    private String name;

    @Column(name = "phone_ext")
    private String phoneExt;

    @Column(name = "phone_no")
    private String phoneNo;

    private String email;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "country")
    private Country country;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "currency")
    private Currency currency;

    @Column(name = "fb_id")
    private String facebookId;

    @Column(name = "google_id")
    private String googleId;

    @Column(name = "current_balance")
    private int currentBalance;

    @Column(name = "is_enabled")
    private boolean isEnabled;

    @Column(name = "free_sample_used")
    private boolean isfreeSampleUsed;

    @Column(name = "client_id")
    private String clientId;

}

My Country Entity:

package com.papertrue.country;

import com.papertrue.currency.Currency;

@Entity
@ConfigurationProperties("country")
@Table(name = "countries")
public class Country {

    @Id
    private String code;

    private String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "currency")
    private Currency currency;

    @Column(name = "isd_ext")
    private String ISDExt;

    @Enumerated(EnumType.STRING)
    private transient Region region;
}

And my Currency Entity:

package com.papertrue.currency;

@Entity
@ConfigurationProperties("currency")
@Table(name = "currencies")
public class Currency {

    @Id
    private String code;

    private String symbol;

    private String name;

    private int multiplier;

    @Column(name = "minVal")
    private int minValue;

}

So it's working when I am mapping Currency with-in the Country object but it's somehow not when I do the same thing with User and Country. I'm getting org.springframework.core.convert.ConverterNotFoundException . Here's the error:

java.lang.IllegalStateException: Failed to load ApplicationContext
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:132) ~[spring-test-5.3.0.jar:5.3.0]
Caused by: org.springframework.boot.context.properties.ConfigurationPropertiesBindException: Error creating bean with name 'user-com.papertrue.user.User': Could not bind properties to 'User' : prefix=user, ignoreInvalidFields=false, ignoreUnknownFields=true; nested exception is org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'user.country' to com.papertrue.country.Country
    ... 70 common frames omitted
Caused by: org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'user.country' to com.papertrue.country.Country
    ... 89 common frames omitted
Caused by: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.String] to type [@javax.persistence.ManyToOne @javax.persistence.JoinColumn com.papertrue.country.Country]
    ... 105 common frames omitted

And this is happening while I'm running the test:

package com.papertrue;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.test.context.SpringBootTest;

import com.papertrue.exceptions.PaperTrueUserNotFoundException;
import com.papertrue.user.UserService;

@SpringBootTest
public class UserServiceTest {

    @Autowired
    private UserService userService;

    @Test
    public void contextLoads() {
        // Testing getEmailInstance
        System.out.println("====== getEmailInstance() ======");
        try {
            System.out.println(userService.getEmailInstance("text@papertrue.com").getName());
        } catch (PaperTrueUserNotFoundException e) {
            e.printStackTrace();
        }

    }

    @SpringBootApplication
    static class TestConfiguration {
    }

}

The UserService Service:

package com.papertrue.user;

import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.stereotype.Service;

import com.papertrue.exceptions.PaperTrueUserNotFoundException;

@Service
@EnableConfigurationProperties(User.class)
public class UserService {

    @Autowired
    private UserRepository userRepository;

    /**
     * Returns user whose email matches to parameter email's value.
     * 
     * @param email
     * @return
     * @throws PaperTrueUserNotFoundException
     */
    public User getEmailInstance(String email) throws PaperTrueUserNotFoundException {

        Optional<User> optional = userRepository.findByEmail(email);

        if (optional.isPresent()) {
            return optional.get();
        }

        throw new PaperTrueUserNotFoundException("User Not Found");
    }

}

And the Repository for reference:

package com.papertrue.user;

import java.util.Optional;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, String> {

    Optional<User> findByEmail(String email);
}

Answer 1

The exception tells you that it can't set the configuration properties as advised by @ConfigurationProperties . Because for country it has a String value (possibly in the application.properties ) but needs a Country and doesn't have a converter for that.

This brings up the question: "What do you try to achieve with the @ConfigurationProperties annotations?"

It is at least unorthodox to use it on JPA entities, because beans and entities are normally two very different things.

So either you should remove the @ConfigurationProperties annotations or register a custom converter as described here: https://www.logicbig.com/tutorials/spring-framework/spring-boot/custom-configuration-properties-binding.html