如何在MongoDB中的第一级数组上使用$ elemMatch？
您可以在一级数组上使用$in运算符代替$elemMatch。语法如下
db.yourCollectionName.find({yourFieldName:{$in:["yourValue"]}}).pretty();首先让我们创建一个包含文档的集合
>db.firstLevelArrayDemo.insertOne({"StudentName":"Chris","StudentTechnicalSkills":["Mongo
DB","MySQL","SQL Server"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca2360f66324ffac2a7dc71")
}
>db.firstLevelArrayDemo.insertOne({"StudentName":"Robert","StudentTechnicalSkills":["C","J
ava","C++"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca2362766324ffac2a7dc72")
}以下是在find()方法的帮助下显示集合中所有文档的查询
> db.firstLevelArrayDemo.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5ca2360f66324ffac2a7dc71"),
"StudentName" : "Chris",
"StudentTechnicalSkills" : [
"MongoDB",
"MySQL",
"SQL Server"
]
}
{
"_id" : ObjectId("5ca2362766324ffac2a7dc72"),
"StudentName" : "Robert",
"StudentTechnicalSkills" : [
"C",
"Java",
"C++"
]
}以下是要在第一级数组上进行匹配的查询
> db.firstLevelArrayDemo.find({StudentTechnicalSkills:{$in:["MongoDB"]}}).pretty();这将产生以下输出
{
"_id" : ObjectId("5ca2360f66324ffac2a7dc71"),
"StudentName" : "Chris",
"StudentTechnicalSkills" : [
"MongoDB",
"MySQL",
"SQL Server"
]
}