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法律学在 MongoDB 中如何查找数组字段不为空的记录？
你可以使用 $ne（不等于）运算符。为了理解这一概念，让我们创建一个带有文档的集合。创建含有该文档的集合的查询如下 −
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Larry","StudentTechnicalSubject":["Java","C"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe2f1e9c5dd6f1f78291")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Mike","StudentTechnicalSubject":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe3b1e9c5dd6f1f78292")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Sam","StudentTechnicalSubject":["MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe491e9c5dd6f1f78293")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"Carol","StudentTechnicalSubject":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe521e9c5dd6f1f78294")
}
> db.arrayFieldIsNotEmptyDemo.insertOne({"StudentName":"David","StudentTechnicalSubject":["MySQL","SQL Server"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c76fe661e9c5dd6f1f78295")
}在集合中使用 find() 方法显示所有文档。查询如下 −
> db.arrayFieldIsNotEmptyDemo.find().pretty();
输出
{
"_id" : ObjectId("5c76fe2f1e9c5dd6f1f78291"),
"StudentName" : "Larry",
"StudentTechnicalSubject" : [
"Java",
"C"
]
}
{
"_id" : ObjectId("5c76fe3b1e9c5dd6f1f78292"),
"StudentName" : "Mike",
"StudentTechnicalSubject" : [ ]
}
{
"_id" : ObjectId("5c76fe491e9c5dd6f1f78293"),
"StudentName" : "Sam",
"StudentTechnicalSubject" : [
"MongoDB"
]
}
{
"_id" : ObjectId("5c76fe521e9c5dd6f1f78294"),
"StudentName" : "Carol",
"StudentTechnicalSubject" : [ ]
}
{
"_id" : ObjectId("5c76fe661e9c5dd6f1f78295"),
"StudentName" : "David",
"StudentTechnicalSubject" : [
"MySQL",
"SQL Server"
]
}以下是如何在 MongoDB 中查找数组字段不为空的记录的查询 −
> db.arrayFieldIsNotEmptyDemo.find({StudentTechnicalSubject:{$exists:true,$ne:[]}}).pretty();输出
{
"_id" : ObjectId("5c76fe2f1e9c5dd6f1f78291"),
"StudentName" : "Larry",
"StudentTechnicalSubject" : [
"Java",
"C"
]
}
{
"_id" : ObjectId("5c76fe491e9c5dd6f1f78293"),
"StudentName" : "Sam",
"StudentTechnicalSubject" : [
"MongoDB"
]
}
{
"_id" : ObjectId("5c76fe661e9c5dd6f1f78295"),
"StudentName" : "David",
"StudentTechnicalSubject" : [
"MySQL",
"SQL Server"
]
}
更新于： 2019 年 7 月 30 日
2 千次以上浏览
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