MongoDB学习02:使用MongoTemplate操作MongoDB

SpringData的官方文档Spring Data MongoDB - Reference Documentation,阅读官方文档永远是最好的学习方法.

MongoTemplate的使用示例

1. 创建SpringBoot项目,在pom.xml中添加依赖如下:

   <dependency>
       
       <groupId>org.springframework.datagroupId>
       <artifactId>spring-data-mongodbartifactId>
   dependency>
   

2. 在cn.maoritian.domain包下创建实体类Preson如下:

   package cn.maoritian.domain;
   
   public class Person {
   
       private String id;
       private String name;
       private int age;
   
       public String getId() {return id; }
       public String getName() {return name; }
       public int getAge() {return age; }
   
       public Person(String name, int age) {this.name = name; this.age = age; }
   
       @Override
       public String toString() {return "Person [id=" + id + ", name=" + name + ", age=" + age + "]"; }
   }
   

3. 在cn.maoritian包下创建SpringBoot启动类MongoApp,在其main()函数中进行对MongoDB的操作

   package cn.maoritian;
   
   import static org.springframework.data.mongodb.core.query.Criteria.where;
   
   import cn.maoritian.domain.Person;
   import org.apache.commons.logging.Log;
   import org.apache.commons.logging.LogFactory;
   import org.springframework.data.mongodb.core.MongoOperations;
   import org.springframework.data.mongodb.core.MongoTemplate;
   import org.springframework.data.mongodb.core.query.Query;
   
   import com.mongodb.MongoClient;
   
   public class MongoApp {
   
       private static final Log log = LogFactory.getLog(MongoApp.class);
   
       public static void main(String[] args) throws Exception {
   
           MongoOperations mongoOps = new MongoTemplate(new MongoClient(), "数据库名");
           mongoOps.insert(new Person("Joe", 34));	// 默认插入进名为person的collection
   
           log.info(mongoOps.findOne(new Query(where("name").is("Joe")), Person.class));
   
           mongoOps.dropCollection("person");
       }
   }
   

   程序输出如下:

   22:35:59.212 [main] DEBUG org.springframework.data.mongodb.core.index.MongoPersistentEntityIndexCreator - Analyzing class class cn.maoritian.domain.Person for index information.
   22:35:59.260 [main] DEBUG org.springframework.data.mongodb.core.MongoTemplate - Inserting Document containing fields: [name, age, _class] in collection: person
   22:35:59.337 [main] DEBUG org.springframework.data.mongodb.core.MongoTemplate - findOne using query: { "name" : "Joe" } fields: Document{{}} for class: class cn.maoritian.domain.Person in collection: person
   22:35:59.372 [main] INFO cn.maoritian.MongoApp - Person [id=5d7e4c39676d91262cdf734f, name=Joe, age=34]
   22:35:59.384 [main] DEBUG framework.data.mongodb.core.MongoTemplate: 375 - Dropped collection [database.person]
   

MongoTemplate的使用

向Spring容器注入MongoTemplate

下面三种方式均可向Spring容器中注入MongoTemplate:

1. 使用.xml文件注入:

   <mongo:mongo-client host="localhost" port="27017"/>
   
   <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
   	<constructor-arg ref="mongoClient"/>
   	<constructor-arg name="databaseName" value="数据库名"/>
   bean>
   

2. 使用Java Config注入:

   @Configuration
   public class AppConfig {
   
       public @Bean MongoClient mongoClient() {
           return new MongoClient("localhost");
       }
   
       public @Bean MongoTemplate mongoTemplate() {
           return new MongoTemplate(mongoClient(), "数据库名");
       }
   }
   

3. 在SpringBoot项目中,还可以使用.yml文件注入

   spring:
     data:
       mongodb:
         uri: mongodb://服务器IP地址:端口号/数据库名
   

   其中,mongodb属性对应的所有yml配置项均为org.springframework.boot.autoconfigure.mongo.MongoProperties类的属性,其源代码如下:

   package org.springframework.boot.autoconfigure.mongo;
   
   import com.mongodb.MongoClientURI;
   import org.springframework.boot.context.properties.ConfigurationProperties;
   
   @ConfigurationProperties(prefix = "spring.data.mongodb")	// 指明yml配置的前缀
   public class MongoProperties {
       public static final int DEFAULT_PORT = 27017;
       public static final String DEFAULT_URI = "mongodb://localhost/test";
       private String host;
       private Integer port = null;
       private String uri;
       private String database;
       private String authenticationDatabase;
       private String gridFsDatabase;
       private String username;
       private char[] password;
       private Class<?> fieldNamingStrategy;
   	
       // get,set方法...
   }
   

字段和类型映射

_id字段映射

MongoDB要求每个文档包含一个_id字段,在实体类中,如下两种属性会被映射为_id字段:

1. 使用@Id注解的属性会被映射为数据库_id字段.
2. 名为id的属性会被映射为数据库_id字段.

_class字段映射

当一个POJO对象被转换为MongoDB中的文档时,会自动在文档末尾加入一个_class字段,其值为该POJO类的全限定类名(fully qualified classname).

下面例子展示一个实体类与其转化为的MongoDB文档间的关系:

public class Sample {
  Contact value;
}

public abstract class Contact { … }

public class Person extends Contact { … }

Sample sample = new Sample();
sample.value = new Person();

mongoTemplate.save(sample);

{
    "value" : { "_class" : "cn.maoritian.Person" },
    "_class" : "cn.maoritian.Sample"
}

如果不想在_class字段中保存整个类名,可以在POJO类上使用@TypeAlias注解,其值为_class字段的值.

@TypeAlias("pers")
class Person {
    ...
}

{
    "value" : { "_class" : "pers" },
    "_class" : "cn.maoritian.Sample"
}

自定义类型映射

通过向Spring容器中注入MongoTypeMapper 的实现类,我们可以配置自定义类型映射.

class CustomMongoTypeMapper extends DefaultMongoTypeMapper {
	//implement custom type mapping here
}

@Configuration
class SampleMongoConfiguration extends AbstractMongoConfiguration {

	@Override
	protected String getDatabaseName() {
		return "数据库名";
	}

	@Override
	public MongoClient mongoClient() {
		return new MongoClient();
	}

	@Bean
	@Override
	public MappingMongoConverter mappingMongoConverter() throws Exception {
		MappingMongoConverter mmc = super.mappingMongoConverter();
		mmc.setTypeMapper(customTypeMapper());
		return mmc;
	}

	@Bean
	public MongoTypeMapper customTypeMapper() {
		return new CustomMongoTypeMapper();
	}
}

使用MongoTemplate进行CRUD

对于每个实体类,MongoTemplate会将其对象存入一个单独的集合(collection)中,该集合的默认集合名为实体类名首字母变小写(如cn.maoritian.Person类的所有实例默认会被存入person集合中).

可以在实体类上加以@Document注解,其collection属性指定将该类的实例对象存入的集合名.

@Document(collection = "集合名")
public class Person {
 	// ...   
}

保存(insert/save)文档的方法

下面三个方法可以向MongoDB中保存文档

• insert(Object objectToSave)和insert(Object objectToSave, String collectionName): 将objectToSave存入MongoDB中,若与集合中现有文档发生_id字段冲突,则报错.
• insertAll(Collection