Spring Data MongoDB实战(上)

本文会详细展示Spring Data MongoDB是如何访问MongoDB数据库的。MongoDB是一个开源的文档型NoSQL数据库，而Spring Data MongoDB是Spring Data的模块之一，专用于访问MongoDB数据库。Spring Data MongoDB模块既提供了基于方法名的查询方式，也提供了基于注释的查询方式。

1、用Spring Data配置并管理MongoDB

要安装MongoDB数据库，可以从这里下载：https://www.mongodb.org/downloads
安装过程省略。完成MongoDB的安装和运行后，可以开始应用开发了。
首先在Eclipse创建一个简单的Maven项目，并配置pom.xml管理Spring Data MongoDB项目的依赖。内容如下：

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>SpringDataMongoDBDemo</groupId>
    <artifactId>SpringDataMongoDBDemo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-mongodb</artifactId>
            <version>1.7.2.RELEASE</version>
        </dependency>
    </dependencies>
</project> 

Eclipse会下载所需的JAR包并把依赖关系配置到项目的类路径下。现在项目的依赖关系已经完成导入，可以开始编写实际的代码了。
首先创建需要持久化到MongoDB数据库的实体类。

Person.java

package com.ch.jpa.entity;

import java.util.ArrayList;
import java.util.List;
import org.springframework.data.annotation.Id;
import org.springframework.data.annotation.PersistenceConstructor;
import org.springframework.data.mongodb.core.mapping.DBRef;
import org.springframework.data.mongodb.core.mapping.Document;

@Document(collection = "person")
public class Person {

    @Id
    private Long personId;

    private String name;

    private int age;

    @DBRef(db = "address")
    private List<Address> addresses = new ArrayList<>();

    public Person() {
    }

    @PersistenceConstructor
    public Person(Long personId, String name, int age) {
        super();
        this.personId = personId;
        this.name = name;
        this.age = age;
    }

    public Long getPersonId() {
        return personId;
    }

    public void setPersonId(Long personId) {
        this.personId = personId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public List<Address> getAddresses() {
        return addresses;
    }

    public void setAddresses(List<Address> addresses) {
        this.addresses = addresses;
    }

    @Override
    public String toString() {
        return "Person [personId=" + personId + ", name=" + name + ", age=" + age + ", addresses=" + addresses + "]";
    }
} 

注释@Document表示待持久化的数据是一个集合。如果集合没有指定名字，那么默认会使用实体类的类名作为集合名。
注释@Id表示被注解的域被映射到集合中的_id列。如果实体类中未使用此注释，那么默认名为id的域会被映射到集合中的_id列。而且此域的值由MongoDB的驱动包自动产生，它的值在在POJO中是不可用的。
注释@DBRef用于在当前的实体类中引用已有的实体类。然而，与关系数据库的情况不同，如果我们保存当前实体，它不会保存引用的相关实体。引用的相关实体的持久化是分开的。
注释@PersistenceConstructor用于标记从MongoDB数据库服务器取回数据时创建实体的构造方法。

下面是关联的Address实体类：

Address.java

package com.ch.jpa.entity;

import org.springframework.data.annotation.Id;
import org.springframework.data.annotation.PersistenceConstructor;
import org.springframework.data.mongodb.core.mapping.Document;

@Document(collection = "address")
public class Address {

    @Id
    private long addressId;

    private String address;

    private String city;

    private String state;

    private long zipcode;

    public Address() {

        System.out.println("CAlling default cons");
    }

    @PersistenceConstructor
    public Address(long addressId, String address, String city, String state, long zipcode) {
        super();
        this.addressId = addressId;
        this.address = address;
        this.city = city;
        this.state = state;
        this.zipcode = zipcode;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public long getZipcode() {
        return zipcode;
    }

    public void setZipcode(long zipcode) {
        this.zipcode = zipcode;
    }

    @Override
    public String toString() {
        return "Address [address=" + address + ", city=" + city + ", state=" + state + ", zipcode=" + zipcode + "]";
    }
}