查询创建Spring Data JPA

Question

我有一堆汽车用品。 我能够呈现所有Car Objects的列表，并且每个字段都显示在list.html 。 如果我只想在list.html上显示make值列表，该如何使用查询来解决？ 查看Spring Data JPA Docs第5.3.2节，我可以做类似findByAllMake();事情findByAllMake(); ？

我尝试过findByAllMake(); ...

以下代码显示了如何成功获取所有对象的完整列表。 希望仅获取所有make的列表。

汽车.java

package com.example.demo;


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


@Entity
public class Car {

    @Id
    private String id;

    private String make;
    private String model;
    private String year;


    public Car() {
    }

    public Car(String id, String make, String model, String year) {
        this.id = id;
        this.make = make;
        this.model = model;
        this.year = year;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getMake() {
        return make;
    }

    public void setMake(String make) {
        this.make = make;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public String getYear() {
        return year;
    }

    public void setYear(String year) {
        this.year = year;
    }
}

CarController.java：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;


@Controller
public class CarController {



    @Autowired
    private CarRepository carRepository;


    @GetMapping("/list")
    public String carMakeList(Model model){
        model.addAttribute("list", carRepository.getAllMakes());

        return "list";
    }


}

CarRepository.java

package com.example.demo;

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

import java.util.List;

@Repository
public interface CarRepository extends JpaRepository<Car, String> {
    @Query(value="SELECT * FROM car;", nativeQuery=true)
    List<Car> getAllMakes();


}

我尝试过findByAllMake(); 但是我又得到了一个不令人满意的依赖错误。

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'carController': Unsatisfied dependency expressed through field 'carService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'carService': Unsatisfied dependency expressed through field 'carRepository'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'carRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Failed to create query for method public abstract java.util.List com.example.demo.CarRepository.findAllByMake()! No parameter available for part make SIMPLE_PROPERTY (1): [Is, Equals] NEVER.

Answer 1

使是字符串。 因此，如果您想让方法返回make列表，则其返回类型应为List<String> ，而不是List<Car> 。

查询需要选择品牌，而不是汽车：

select distinct car.make from Car car

Answer 2

还没有在我的笔记本电脑上运行它，但是如果您尝试执行以下操作：向CarController添加构造函数：

public CarController(CarRepository carRepository){
this.carRepository = carRepository;
}

然后可能只是尝试：

public List<Car> findAll();

在仓库中？