查找數組字段不爲空的MongoDB記錄

本文翻譯自：Find MongoDB records where array field is not empty

All of my records have a field called "pictures". 我所有的記錄都有一個名爲“圖片”的字段。 This field is an array of strings. 該字段是字符串數組。

I now want the newest 10 records where this array IS NOT empty. 我現在想要該數組不爲空的最新10條記錄。

I've googled around, but strangely enough I haven't found much on this. 我在Google上四處搜尋，但奇怪的是，我在這方面沒有發現太多。 I've read into the $where option, but I was wondering how slow that is to native functions, and if there is a better solution. 我已經讀過$ where選項，但是我想知道這對本機函數有多慢，以及是否有更好的解決方案。

And even then, that does not work: 即使這樣，它也不起作用：

ME.find({$where: 'this.pictures.length > 0'}).sort('-created').limit(10).execFind()

Returns nothing. 不返回任何內容。 Leaving this.pictures without the length bit does work, but then it also returns empty records, of course. 留下this.pictures沒有長度位的確可以，但是當然它也返回空記錄。

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#1樓

參考：https://stackoom.com/question/103TI/查找數組字段不爲空的MongoDB記錄

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#2樓

經過一番摸索之後，尤其是在mongodb文檔中，又使人困惑不解，這就是答案：

ME.find({pictures: {$exists: true, $not: {$size: 0}}})

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#3樓

這也可能對您有用：

ME.find({'pictures.0': {$exists: true}});

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#4樓

If you also have documents that don't have the key, you can use: 如果您還有沒有密鑰的文檔，則可以使用：

ME.find({ pictures: { $exists: true, $not: {$size: 0} } })

MongoDB don't use indexes if $size is involved, so here is a better solution: 如果涉及$ size，MongoDB不會使用索引，因此這是一個更好的解決方案：

ME.find({ pictures: { $exists: true, $ne: [] } })

Since MongoDB 2.6 release, you can compare with the operator $gt but could lead to unexpected results (you can find a detailled explanation in this answer ): 從MongoDB 2.6版本開始，您可以與運算符$gt進行比較，但可能會導致意外的結果（您可以在此答案中找到詳細的說明）：

ME.find({ pictures: { $gt: [] } })

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#5樓

Starting with the 2.6 release, another way to do this is to compare the field to an empty array: 從2.6版本開始，另一種方法是將字段與一個空數組進行比較：

ME.find({pictures: {$gt: []}})

Testing it out in the shell: 在外殼中進行測試：

> db.ME.insert([
{pictures: [1,2,3]},
{pictures: []},
{pictures: ['']},
{pictures: [0]},
{pictures: 1},
{foobar: 1}
])

> db.ME.find({pictures: {$gt: []}})
{ "_id": ObjectId("54d4d9ff96340090b6c1c4a7"), "pictures": [ 1, 2, 3 ] }
{ "_id": ObjectId("54d4d9ff96340090b6c1c4a9"), "pictures": [ "" ] }
{ "_id": ObjectId("54d4d9ff96340090b6c1c4aa"), "pictures": [ 0 ] }

So it properly includes the docs where pictures has at least one array element, and excludes the docs where pictures is either an empty array, not an array, or missing. 因此，它適當地包括pictures至少具有一個數組元素的docs，並排除pictures爲空數組，不是數組或缺失的docs。

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#6樓

ME.find({pictures: {$exists: true}}) 

就這麼簡單，這對我有用。