如何通过MongoDB的键名检索值？
要通过MongoDB的键名检索值，请使用以下语法-
db.yourCollectionName.find({},{"yourFieldName":1}).pretty();为了理解上述语法，让我们用文档创建一个集合。使用文档创建集合的查询如下-
> db.retrieveValueFromAKeyDemo.insertOne({"CustomerName":"Larry","CustomerAge":21,"CustomerCountryName":"US"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9163b5a56efcc0f9e69048")
}
> db.retrieveValueFromAKeyDemo.insertOne({"CustomerName":"Chris","CustomerAge":24,"CustomerCountryName":"AUS"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9163c4a56efcc0f9e69049")
}
> db.retrieveValueFromAKeyDemo.insertOne({"CustomerName":"Mike","CustomerAge":26,"CustomerCountryName":"UK"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9163d3a56efcc0f9e6904a")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.retrieveValueFromAKeyDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c9163b5a56efcc0f9e69048"),
"CustomerName" : "Larry",
"CustomerAge" : 21,
"CustomerCountryName" : "US"
}
{
"_id" : ObjectId("5c9163c4a56efcc0f9e69049"),
"CustomerName" : "Chris",
"CustomerAge" : 24,
"CustomerCountryName" : "AUS"
}
{
"_id" : ObjectId("5c9163d3a56efcc0f9e6904a"),
"CustomerName" : "Mike",
"CustomerAge" : 26,
"CustomerCountryName" : "UK"
}这是通过键名称从MongoDB检索值的查询，即我们已经考虑了键'CustomerCountryName'-
> db.retrieveValueFromAKeyDemo.find({},{"CustomerCountryName":1}).pretty();以下是输出：
{
"_id" : ObjectId("5c9163b5a56efcc0f9e69048"),
"CustomerCountryName" : "US"
}
{
"_id" : ObjectId("5c9163c4a56efcc0f9e69049"),
"CustomerCountryName" : "AUS"
}
{
"_id" : ObjectId("5c9163d3a56efcc0f9e6904a"),
"CustomerCountryName" : "UK"
}