SpringBoot v2.x MongodB 中 去除 _class 字段

 在使用SpringBoot中使用MongoTemplate时，数据库中数据会有_class字段.。_class的意义，在下面这个链接有很好的解答： 
http://stackoverflow.com/questions/6810488/spring-data-mongodb-mappingmongoconverter-remove-class/ 
，其实就是说，为了在把document转换成Java对象时能够转换到具体的子类.。
要去掉的方法简单：DefaultMongoTypeMapper类的构造函数的第一个参数是Type在MongoDB中名字. 设置为null的话就不会在保存时自动添加_class属性.所以需要覆写 

以下就是去除_class 字段的配置类，只需将代码复制即可直接使用。

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.convert.CustomConversions;
import org.springframework.data.mongodb.MongoDbFactory;
import org.springframework.data.mongodb.core.convert.DbRefResolver;
import org.springframework.data.mongodb.core.convert.DefaultDbRefResolver;
import org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper;
import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
 
/**
 * Create by JIUN·LIU at 2018/7/24
 */
 
@Configuration
public class MongoConfig {
 
    @Bean
    public MappingMongoConverter mappingMongoConverter(MongoDbFactory factory, MongoMappingContext context, BeanFactory beanFactory) {
        DbRefResolver dbRefResolver = new DefaultDbRefResolver(factory);
        MappingMongoConverter mappingConverter = new MappingMongoConverter(dbRefResolver, context);
        try {
            mappingConverter.setCustomConversions(beanFactory.getBean(CustomConversions.class));
        } catch (NoSuchBeanDefinitionException ignore) {
        }
 
        // Don't save _class to mongo
        mappingConverter.setTypeMapper(new DefaultMongoTypeMapper(null));
 
        return mappingConverter;
    }
 
}

如果不是spring boot项目则可以用xml配置。

<mongo:mongo host="localhost" port="27017" />
<mongo:db-factory dbname="database" />
 <bean id="mappingContext"
    class="org.springframework.data.mongodb.core.mapping.MongoMappingContext" />
 <bean id="defaultMongoTypeMapper"
    class="org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper">
    <constructor-arg name="typeKey"><null/></constructor-arg>
 </bean>
 <bean id="mappingMongoConverter"
    class="org.springframework.data.mongodb.core.convert.MappingMongoConverter">
    <constructor-arg name="mongoDbFactory" ref="mongoDbFactory" />
    <constructor-arg name="mappingContext" ref="mappingContext" />
    <property name="typeMapper" ref="defaultMongoTypeMapper" />
 </bean>
 <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
    <constructor-arg name="mongoDbFactory" ref="mongoDbFactory" />
    <constructor-arg name="mongoConverter" ref="mappingMongoConverter" />
 </bean>