Question

我从这个例子开始：https://spring.io/guides/gs/accessing-data-mongodb/#initial
一切都很好，但我注意到mongodb没有保存数据！因为当我第二次运行程序时没有保存＆＃34;客户＆＃34; （在示例中），它返回null！

// save a couple of customers
repository.save(new Customer("Alice", "Smith"));
repository.save(new Customer("Bob", "Smith"));

感谢您的帮助。编辑：

package hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application implements CommandLineRunner {

    @Autowired
    private CustomerRepository repository;

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Override
    public void run(String... args) throws Exception {

        repository.deleteAll();

        // save a couple of customers
        repository.save(new Customer("Alice", "Smith"));
        repository.save(new Customer("Bob", "Smith"));

        // fetch all customers
        System.out.println("Customers found with findAll():");
        System.out.println("-------------------------------");
        for (Customer customer : repository.findAll()) {
            System.out.println(customer);
        }
        System.out.println();

        // fetch an individual customer
        System.out.println("Customer found with findByFirstName('Alice'):");
        System.out.println("--------------------------------");
        System.out.println(repository.findByFirstName("Alice"));

        System.out.println("Customers found with findByLastName('Smith'):");
        System.out.println("--------------------------------");
        for (Customer customer : repository.findByLastName("Smith")) {
            System.out.println(customer);
        }

    }

}

package hello;

import org.springframework.data.annotation.Id;


public class Customer {

    @Id
    private String id;

    private String firstName;
    private String lastName;

    public Customer() {}

    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return String.format(
                "Customer[id=%s, firstName='%s', lastName='%s']",
                id, firstName, lastName);
    }

}

package hello;

import java.util.List;

import org.springframework.data.mongodb.repository.MongoRepository;

public interface CustomerRepository extends MongoRepository<Customer, String> {

    public Customer findByFirstName(String firstName);
    public List<Customer> findByLastName(String lastName);

}

Answer 1

首先，请确保您的说明没有像您发布的代码段那样被注释掉。

然后请务必从示例中删除repository.deleteAll();（下次提供完整代码）

然后注意接口findByXxx的{{1}}方法将自动创建代码，以使用名为MongoRepository的变量和指定值搜索对象。如果该变量拼写错误，不确定会发生什么。

mongodb没有保存第二次运行程序的数据

1 个答案: