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Legal Studies在 MongoDB 中查詢沒有某個欄位的條目？
要查詢沒有某個欄位的條目，請使用 $exists 運算子。語法如下 −
> db.yourCollectionName.find({"yourItemName":{$exists:false}}).pretty();為理解語法，讓我們透過文件建立一個集合。建立帶文件的集合的查詢如下 −
> db.findDocumentDoNotHaveCertainFields.insertOne({"UserId":101,"UserName":"John","UserAge":21});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8a95fb6cea1f28b7aa07fb")
}
> db.findDocumentDoNotHaveCertainFields.insertOne({"UserName":"David","UserAge":22,"UserFavouriteSubject":["C","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8a96116cea1f28b7aa07fc")
}
> db.findDocumentDoNotHaveCertainFields.insertOne({"UserName":"Bob","UserAge":24,"UserFavouriteSubject":["MongoDB","MySQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8a96306cea1f28b7aa07fd")
}藉助 find() 方法從一個集合裡展示所有文件。查詢如下 −
> db.findDocumentDoNotHaveCertainFields.find().pretty();
輸出如下 −
{
"_id" : ObjectId("5c8a95fb6cea1f28b7aa07fb"),
"UserId" : 101,
"UserName" : "John",
"UserAge" : 21
}
{
"_id" : ObjectId("5c8a96116cea1f28b7aa07fc"),
"UserName" : "David",
"UserAge" : 22,
"UserFavouriteSubject" : [
"C",
"Java"
]
}
{
"_id" : ObjectId("5c8a96306cea1f28b7aa07fd"),
"UserName" : "Bob",
"UserAge" : 24,
"UserFavouriteSubject" : [
"MongoDB",
"MySQL"
]
}這裡有一個查詢，它可以找到沒有 UserFavouriteSubject 欄位的條目 −
> db.findDocumentDoNotHaveCertainFields.find({"UserFavouriteSubject":{$exists:false}}).pretty();輸出如下 −
{
"_id" : ObjectId("5c8a95fb6cea1f28b7aa07fb"),
"UserId" : 101,
"UserName" : "John",
"UserAge" : 21
}
更新於：2019-07-30
129 次瀏覽
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