在MongoDB中查询数组大小大于1的文档？
您可以使用长度查询数组大小大于1的文档：
db.yourCollectionName.find({$where:"this.yourArrayDocumentName.length > 1"}).pretty();为了理解上述语法，让我们创建包含一些文档的集合。查询如下以创建包含文档的集合：
>db.arrayLengthGreaterThanOne.insertOne({"StudentName":"Larry","StudentTechnicalSubje
ct":["Java","C","C++"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c6d6c4c0c3d5054b766a76a")
}
>db.arrayLengthGreaterThanOne.insertOne({"StudentName":"Maxwell","StudentTechnicalSu
bject":["MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c6d6c660c3d5054b766a76b")
}
>db.arrayLengthGreaterThanOne.insertOne({"StudentName":"Maxwell","StudentTechnicalSu
bject":["MySQL","SQL Server","PL/SQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c6d6c800c3d5054b766a76c")
}在find()method的帮助下显示集合中的所有文档。查询如下：
> db.arrayLengthGreaterThanOne.find().pretty();
以下是输出：
{
"_id" : ObjectId("5c6d6c4c0c3d5054b766a76a"),
"StudentName" : "Larry",
"StudentTechnicalSubject" : [
"Java",
"C",
"C++"
]
}
{
"_id" : ObjectId("5c6d6c660c3d5054b766a76b"),
"StudentName" : "Maxwell",
"StudentTechnicalSubject" : [
"MongoDB"
]
}
{
"_id" : ObjectId("5c6d6c800c3d5054b766a76c"),
"StudentName" : "Maxwell",
"StudentTechnicalSubject" : [
"MySQL",
"SQL Server",
"PL/SQL"
]
}这是对数组大小大于1的文档的查询。以下查询将给出数组大小大于1的所有文档：
> db.arrayLengthGreaterThanOne.find({$where:"this.StudentTechnicalSubject.length > 1"}).pretty();以下是输出：
{
"_id" : ObjectId("5c6d6c4c0c3d5054b766a76a"),
"StudentName" : "Larry",
"StudentTechnicalSubject" : [
"Java",
"C",
"C++"
]
}
{
"_id" : ObjectId("5c6d6c800c3d5054b766a76c"),
"StudentName" : "Maxwell",
"StudentTechnicalSubject" : [
"MySQL",
"SQL Server",
"PL/SQL"
]
}