Question

我有几个型号：User和UserTags

A User has_many UserTags
A UserTag belongs_to User

我正在尝试找到所有Users没有UserTag名称＆＃39;记录＆＃39; （所以我也想要那些根本没有任何标签的用户）。鉴于用户关系，我有这个：

users.joins("LEFT OUTER JOIN user_tags ON user_tags.user_id = users.id AND user_tags.name = 'recorded'").
where(user_tags: { id: nil })

还有其他更好或更多的Railsy方法吗？

Answer 1

试试这个：

users.joins("LEFT OUTER JOIN user_tags ON user_tags.user_id=users.id").where("user_tags.name != ? OR user_tags.id is NULL", 'recorded')

Answer 2

这个应该有效：

    Sending value: hi of type class demo.domain.Foo
2016-04-07 19:19:50.811 ERROR 76016 --- [hannel-adapter1] o.s.c.s.b.r.RedisMessageChannelBinder$2  : Failed to deliver message; retries exhausted; message sent to queue 'ERRORS:testtock.anonymous.61fc01c4-17a1-46b5-9579-286413dc45e0' 

org.springframework.messaging.converter.MessageConversionException: No converter found to convert to class demo.domain.Bar, message=GenericMessage [payload=hi, headers={contentType=text/plain, id=72274970-5e79-a8ef-d3f1-fcd4ede2fa55, timestamp=1460027990799}]
    at org.springframework.messaging.handler.annotation.support.PayloadArgumentResolver.resolveArgument(PayloadArgumentResolver.java:118) ~[spring-messaging-4.2.5.RELEASE.jar!/:4.2.5.RELEASE]
    at org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:98) ~[spring-messaging-4.2.5.RELEASE.jar!/:4.2.5.RELEASE]
    at org.springframework.messaging.handler.invocation.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:138) ~[spring-messaging-4.2.5.RELEASE.jar!/:4.2.5.RELEASE]
    at org.springframework.messaging.handler.invocation.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:107) ~[spring-messaging-4.2.5.RELEASE.jar!/:4.2.5.RELEASE]
    at org.springframework.cloud.stream.binding.StreamListenerAnnotationBeanPostProcessor$StreamListenerMessageHandler.handleRequestMessage(StreamListenerAnnotationBeanPostProcessor.java:192) ~[spring-cloud-stream-1.0.0.RC1.jar!/:1.0.0.RC1]
    at org.springframework.integration.handler.AbstractReplyProducingMessageHandler.handleMessageInternal(AbstractReplyProducingMessageHandler.java:99) ~[spring-integration-core-4.2.5.RELEASE.jar!/:na]

Answer 3

试试这个，它将返回0 user_tags：

的用户

users = users.joins(:user_tag).where("users.id IN (?) OR user_tags.name != ?",User.joins(:user_tag).group("users.id").having('count("user_tag.user_id") = 0'), "recorded")

Answer 4

加入不应该使用的加载嵌套模型＆＃34;包含或eage_load＆＃34;

 users.eager_load(:user_tags).where.not(user_tags: { name: 'recorded' })

这将使用左外连接，您可以在where子句中更新您的查询。与

相同

users.includes(:user_tags).where.not(user_tags: { name: 'recorded' })

Answer 5

嘿，您可以简单地使用includes进行外部联接，因为user_tags.id is null会返回所有没有user_tags的记录，user_tags.name != 'recorded'会返回记录，而user_tag名称不是{{1} }

recorded

或者您也可以使用users.includes(:user_tags).where("user_tags.id is null or user_tags.name != ?","recorded")子句，但它不是给定查询的优化方式：

not in

查找没有任何具有特定值的关联记录的记录

5 个答案: