按值或默认值查询 [英] Mongoid query by value or default value

问题描述

我刚刚用布尔值字段更新了我的一个模型.我已将字段的默认值设置为true.如何以一种方式查询此字段，以使所有将该字段设置为true或没有此字段(默认值)的文档.

I've just updated one of my models with a boolean field. I've set a default value for the field to true. How can I query for this field in such a way that I get all documents with this field set to true or doesn't have this field (default value).

推荐答案

要查找没有具有特定密钥的文档，您想使用

To find documents that don't have a particular key, you want to use $exists:

$存在
语法:{ field: { $exists: <boolean> } }

$exists
Syntax: { field: { $exists: <boolean> } }

$exists选择包含该字段的文档.如果<boolean>为false，则查询仅返回不包含该字段的文档. $exists与包含包含null值的字段的文档匹配.

$exists selects the documents that contain the field if <boolean> is true. If <boolean> is false, the query only returns the documents that do not contain the field. $exists does match documents that contain the field that stores the null value.

因此，存在检查将如下所示:

So the existence check would look like:

Model.where(:field.exists => false)
Model.where(:field => { :$exists => false })

请注意，第一个:field.exists表单在发送到MongoDB之前变成了第二个表单；我之所以这样说是因为，如果不使用$and或$or来组合这些子句，就无法在查询的其他地方使用:field::field.exists扩展会导致查询中的键哈希相互覆盖.您不会在这里遇到这个问题，但提醒不会受到伤害.

Note that the first :field.exists form becomes the second form before it gets sent to MongoDB; I mention this because you won't be able to use :field elsewhere in the query without using $and or $or to combine the clauses: the :field.exists expansion can lead to keys in the query Hash overwriting each other. You won't have this problem here but a reminder can't hurt.

查找true很容易:

Model.where(:field => true)

您想要其中一个，因此可以将它们与 $or结合使用:

You want either one so combine them with $or:

Model.where(:$or => [
  { :field.exists => false },
  { :field        => true  }
])

如果:field可能存在但具有null值，则可以使用{ :field => nil }匹配:field为null 或根本不存在的文档:

If :field might be there but have a null value then you could use { :field => nil } to match documents where :field is null or not there at all:

Model.where(:$or => [
  { :field => null  },
  { :field => true  }
])
# or
Model.where(:field.in => [ null, true ]) # This is probably the one you want

如果您正在查找和明确显示的null内容，也有{ :field => { :$type => 10 } }.现在可能是快速回顾MongoDB常见问题的好时机:

There's also { :field => { :$type => 10 } } if you're looking for things that are there and explicitly null. Now might be a good time for a quick review of the MongoDB FAQ:

如何查询字段包含空值?

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