插入到MongoDB数组的特定索引？
要为MongoDB数组插入特定索引，可以使用$push运算符。让我们创建包含文档的集合
>db.insertToSpecificIndexDemo.insertOne({"StudentName":"Larry","StudentSubjects":["MySQL","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d2562a629b87623db1b2c")
}
>db.insertToSpecificIndexDemo.insertOne({"StudentName":"Chris","StudentSubjects":["C++","C"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d2573a629b87623db1b2d")
}以下是查询以借助find()方法显示集合中的所有文档
> db.insertToSpecificIndexDemo.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5c9d2562a629b87623db1b2c"),
"StudentName" : "Larry",
"StudentSubjects" : [
"MySQL",
"Java"
]
}
{
"_id" : ObjectId("5c9d2573a629b87623db1b2d"),
"StudentName" : "Chris",
"StudentSubjects" : [
"C++",
"C"
]
}以下是在_id“5c9d2573a629b87623db1b2d”中插入到MongoDB数组的特定索引的查询
> db.insertToSpecificIndexDemo.update(
... { _id: ObjectId("5c9d2573a629b87623db1b2d")},
... { $push: {
... StudentSubjects: {
... $each: [ {"CoreSubject": "MongoDB"} ],
... $position: 0
... }
... }}
... );
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们检查该值是否插入到特定位置。上面，我们给索引0表示在开头插入
> db.insertToSpecificIndexDemo.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5c9d2562a629b87623db1b2c"),
"StudentName" : "Larry",
"StudentSubjects" : [
"MySQL",
"Java"
]
}
{
"_id" : ObjectId("5c9d2573a629b87623db1b2d"),
"StudentName" : "Chris",
"StudentSubjects" : [
{
"CoreSubject" : "MongoDB"
},
"C++",
"C"
]
}查看示例输出，将“CoreSubject”：“MongoDB”插入到MongoDB数组的开头。