这个问题整整折腾了我两天，现在记录下来，希望可以帮助和我一样，遇到相同问题的小伙伴。
项目是分层的（Intellij IDEA中的模块Module），有API（Core）层，Service&Dao，Common，Model，上一张项目结构图。（不要在意为什么Service和Dao放在一起。这不是重点。）
API中包括了Controller，Mongodb在Service&Dao层中，也就是API层，调用Service&Dao层，我敢用性命担保，所有注释，逻辑，都没有错，但是运行SpringBoot的时候，偏偏报错。（找不到依赖，就是注入失败。）
代码中继承了MongoRepository接口
public interface IUserGroupRepository extends MongoRepository<UserGroup, Integer> {
UserGroup findById(Integer id);
}
报错内容如下：
2017-06-28 10:11:52.423 WARN 8648 --- [ main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt:
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userGroupController': Unsatisfied dependency expressed through field 'userGroupRepository'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.iboxpay.nosql.mongodb.IUserGroupRepository' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} 2017-06-28 10:11:52.426 INFO 8648 --- [ main] o.apache.catalina.core.StandardService : Stopping service [Tomcat] 2017-06-28 10:11:52.446 INFO 8648 --- [ main] utoConfigurationReportLoggingInitializer : Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled. 2017-06-28 10:11:52.591 ERROR 8648 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter : *************************** APPLICATION FAILED TO START *************************** Description: Field userGroupRepository in com.iboxpay.ops.api.controller.UserGroupController required a bean of type 'com.iboxpay.nosql.mongodb.IUserGroupRepository' that could not be found. Action: Consider defining a bean of type 'com.iboxpay.nosql.mongodb.IUserGroupRepository' in your configuration.
解决办法如下：
@SpringBootApplication(scanBasePackages = {"com.iboxpay.service", "com.iboxpay.ops.api", "com.iboxpay.nosql"})
@EnableMongoRepositories(basePackages = {"com.iboxpay.nosql"})
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
因为我的项目是分层的，SpringBoot的@SpringBootApplication注解要添加扫描包，否则有的地方可能会注入失败。另外一点比较重要，需要使有和Mongodb的@EnableMongoRepositories注解，并指定要扫描的包（IUserGroupRepository所在的包，即继承
MongoRepository接口的接口中所在的包。）
上面两个com.iboxpay.nosql缺一不可。切记，切记。