If @RequestParameter is given, filter by it's value, if not do nothing-CodePudding

I'm trying to use @RequestParam, and if the value is given it should filter from all items found in the database by this parameter, if not it should do nothing. I would also like to ask if functional programming is a good use here.

This is my Car class:

import lombok.AccessLevel;
import lombok.Data;
import lombok.Setter;

import javax.persistence.*;

@Data
@Entity
@Table(name = "Cars")
public class Car {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Setter(AccessLevel.NONE)
    private Long Id;

    private int yearOfProduction;
    private int price;
    private String color;
    private String brand;
    private String model;

    @ManyToOne
    @JoinColumn(name = "customer")
    private Customer customer;

    public Car() {
    }

    public Car(int yearOfProduction, int price, String color, String brand, String model) {
        this.yearOfProduction = yearOfProduction;
        this.price = price;
        this.color = color;
        this.brand = brand;
        this.model = model;
    }
}

This is the Controller where I set the parameters to ask for:

@GetMapping
public List<Car> getCars(@RequestParam(required = false) Integer minPrice,
                         @RequestParam(required = false) Integer maxPrice,
                         @RequestParam(required = false) String model){

    return carService.getCars(minPrice, maxPrice, model);
}

This is Car Service and what I would like to do:

public List<Car> getCars(Integer minPrice, Integer maxPrice, String model) {
    return carRepository
            .findAll()
            .stream()
            .filter(car ->
                      //if minPrice exists
                                car.getPrice() >= minPrice
                                 &&
                       //if maxPrice exists
                                 car.getPrice() <= maxPrice
                                 &&
                       //if model exists
                                 car.getModel().equals(model))
                      .collect(Collectors.toList());
}

I could set @RequestParam (defaultValue = "something") in controller, but it's problematic since I don't know what are the default values for "model" field, because every Car has a different model, and still I have to filter items by default values, and it's not needed since I don't want to do anything with that if it's not given.

I was also trying to pass Optional<> as the parameters and then check every parameter with if statement and ifPresent() method in filter function, but I don't how how to bring it together.

CodePudding user response：

You can create a jpa query like this (in your car repository):

@Query("select c from Car c where (?1 is null or c.price >= ?1) and (?2 is null or c.price <= ?2) and (?3 is null or c.model = ?3)")
List<Car> getCars(Integer minPrice, Integer maxPrice, String model);

and then call it from your CarService:

public List<Car> getCars(Integer minPrice, Integer maxPrice, String model) {
   return carRepository.getCars(minPrice, maxPrice, model);
}

One way to circumvent cast problem in postgresql, is to use default values for the params. Say you set 0 as default value for min price and max price and empty string for model.

@Query("select c from Car c where (?1 = 0 or c.price >= ?1) and (?2 = 0 or c.price <= ?2) and (?3 = '' or c.model = ?3)")
List<Car> getCars(Integer minPrice, Integer maxPrice, String model);

And in your controller:

@RequestParam(defaultValue="") String model
@RequestParam(defaultValue="0") Integer minPrice
@RequestParam(defaultValue="0") Integer maxPrice