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法律學在 MongoDB 中如何查詢陣列欄位不為空的記錄？
你可以使用 $ne（不等於）運算子。為了理解這一概念，讓我們建立一個帶有文件的集合。建立含有該文件的集合的查詢如下 −
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Larry","StudentTechnicalSubject":["Java","C"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe2f1e9c5dd6f1f78291")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Mike","StudentTechnicalSubject":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe3b1e9c5dd6f1f78292")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Sam","StudentTechnicalSubject":["MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe491e9c5dd6f1f78293")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Carol","StudentTechnicalSubject":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe521e9c5dd6f1f78294")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"David","StudentTechnicalSubject":["MySQL","SQL Server"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe661e9c5dd6f1f78295")
}在集合中使用 find() 方法顯示所有文件。查詢如下 −
> db.arrayFieldIsNotEmptyDemo.find().pretty();
輸出
{
"_id" : ObjectId("5c76fe2f1e9c5dd6f1f78291"),
"StudentName" : "Larry",
"StudentTechnicalSubject" : [
"Java",
"C"
]
}
{
"_id" : ObjectId("5c76fe3b1e9c5dd6f1f78292"),
"StudentName" : "Mike",
"StudentTechnicalSubject" : [ ]
}
{
"_id" : ObjectId("5c76fe491e9c5dd6f1f78293"),
"StudentName" : "Sam",
"StudentTechnicalSubject" : [
"MongoDB"
]
}
{
"_id" : ObjectId("5c76fe521e9c5dd6f1f78294"),
"StudentName" : "Carol",
"StudentTechnicalSubject" : [ ]
}
{
"_id" : ObjectId("5c76fe661e9c5dd6f1f78295"),
"StudentName" : "David",
"StudentTechnicalSubject" : [
"MySQL",
"SQL Server"
]
}以下是如何在 MongoDB 中查詢陣列欄位不為空的記錄的查詢 −
> db.arrayFieldIsNotEmptyDemo.find({StudentTechnicalSubject:{$exists:true,$ne:[]}}).pretty();輸出
{
"_id" : ObjectId("5c76fe2f1e9c5dd6f1f78291"),
"StudentName" : "Larry",
"StudentTechnicalSubject" : [
"Java",
"C"
]
}
{
"_id" : ObjectId("5c76fe491e9c5dd6f1f78293"),
"StudentName" : "Sam",
"StudentTechnicalSubject" : [
"MongoDB"
]
}
{
"_id" : ObjectId("5c76fe661e9c5dd6f1f78295"),
"StudentName" : "David",
"StudentTechnicalSubject" : [
"MySQL",
"SQL Server"
]
}
更新於： 2019 年 7 月 30 日
2 千次以上瀏覽
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