Spring Boot JPA Entity class variable not found

Question

I'm getting an error where the entity class's variable is not found while the variable is clearly there and the entity class is found

@RestController
public class LanguageController {
    

    @Autowired
    private LanguageService service;
    
    @RequestMapping("/language")
    public List<Language> allLanguages() {
        return service.getAllLanguages();
        }
    
    @RequestMapping("/language/{id}")
    public Optional<Language> allLanguagesById(@PathVariable String id) {
        return service.getLanguagesById(id);    
    }
    


    @RequestMapping(value = "/language", method = RequestMethod.POST)
    public void addTopic(@RequestBody Language topic) { 
        service.addLanguage(topic);
    }
    
    // addLanguage used to save/add depending if obj already exists
    // Will need more variable in obj for it to truly update
    @RequestMapping(value = "/language/{id}", method = RequestMethod.PUT)
    public void updateTopic(@RequestBody Language lang) {
        service.addLanguage(lang);
    }
    

    @RequestMapping(value = "/language/{id}", method = RequestMethod.DELETE)
    public void deleteTopics(@PathVariable String id) {
        service.deleteLanguage(id);
    }
    
    
}

entity class

package com.Alex.language;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

import com.Alex.language.Language;

// JPA to create columns according it
// Act as table labels
@Entity
public class Topics {
    
    // Mark primary key
    @Id
    private String id;
    private String name;
    private String description;
    
    // Many topics to one language
    @ManyToOne
    private Language lang;
    
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    
    public Topics() {
        
    }
    public Topics(String id, String name, String description, String langId) {
        super();
        this.id = id;
        this.name = name;
        this.description = description;
        this.lang = new Language(langId);
    }
    public Language getLang() {
        return lang;
    }

    public void setLang(Language lang) {
        this.lang = lang;
    }

}

  package com.Alex.language;

import javax.persistence.Entity;
import javax.persistence.Id;
@Entity
public class Language { 

    @Id
    private String langId;


    
    public String getLangId() {
        return langId;
    }

    public void setLangId(String langId) {
        this.langId = langId;
    }

    public Language(String langId) {
        super();
        this.langId = langId;
    }

public Language() {
        
    }
}

Controller class

package com.Alex.language;

import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.Alex.language.Language;

// Used to create RESTful web services
@RestController
public class TopicsController {
    
    // As the database is embedded, will have to add data before able to see in Postman
    @Autowired
    private TopicService service;
    
    @RequestMapping("/language/{id}/topics")
    public List<Topics> getAllTopics(@PathVariable String id) {
        return service.getAllTopicsByLanguageId(id);
        }
        
    // @PathVariable get variable from @RequestMapping {id}
    @RequestMapping("/language/{langId}/topics/{id}")
    public Optional<Topics> getSpecifiedTopic(@PathVariable String id) {
        return service.getTopic(id);    
    }
    
    
    // @RequestBody to convert JSON object to Java object to be used
    @RequestMapping(value = "/language/{langId}/topics", method = RequestMethod.POST)
    public void addTopic(@RequestBody Topics topic, @PathVariable String langId) {  
        topic.setLang(new Language(langId));
        service.addTopic(topic);
    }
    
    @RequestMapping(value = "/language/{langId}/topics/{id}", method = RequestMethod.PUT)
    public void updateTopic(@PathVariable String langId, @RequestBody Topics topic) {
        topic.setLang(new Language(langId));
        service.updateTopic(topic);
    }
    
    @RequestMapping(value = "/language/{langId}/topics/{id}", method = RequestMethod.DELETE)
    public void deleteTopics(@PathVariable String id) {
        service.deleteTopic(id);
    }
    
    
}

So, I get the following error message when I type in the url something like this in Postman. localhost:8080/language/java/topics ( POST )

message=Unable to find com.Alex.language.Language with id langId; nested exception is javax.persistence.EntityNotFoundException: Unable to find com.Alex.language.Language with id langId, path=/language/java/topics}]

EDIT: Remove " " between langId which makes a literal String. Silly me, this is one of the mistakes I make most commonly :/

Solving that, I'm getting " Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'langId' in value "/language/${langId}/topics/{id}". I believe there is some configuration problem in main or so.