返回MongoDB中的特定字段？
要返回特定字段，请使用find()MongoDB中的方法。首先让我们创建一个包含文档的集合-
> db.specificFieldDemo.insertOne({"FirstName":"John","LastName":"Doe"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cb8019a623186894665ae31")
}
> db.specificFieldDemo.insertOne({"FirstName":"John","LastName":"Smith"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cb801ab623186894665ae32")
}
> db.specificFieldDemo.insertOne({"FirstName":"David","LastName":"Miller"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cb801b3623186894665ae33")
}
> db.specificFieldDemo.insertOne({"FirstName":"Sam","LastName":"Williams"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cb801bf623186894665ae34")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.specificFieldDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cb8019a623186894665ae31"),
"FirstName" : "John",
"LastName" : "Doe"
}
{
"_id" : ObjectId("5cb801ab623186894665ae32"),
"FirstName" : "John",
"LastName" : "Smith"
}
{
"_id" : ObjectId("5cb801b3623186894665ae33"),
"FirstName" : "David",
"LastName" : "Miller"
}
{
"_id" : ObjectId("5cb801bf623186894665ae34"),
"FirstName" : "Sam",
"LastName" : "Williams"
}以下是返回特定字段的查询。在这里，我们返回字段“LastName”-
> db.specificFieldDemo.find({},{_id:0,LastName:1});这将产生以下输出-
{ "LastName" : "Doe" }
{ "LastName" : "Smith" }
{ "LastName" : "Miller" }
{ "LastName" : "Williams" }