MongoDB查询单个字段
对于单个字段，请使用find()。首先让我们创建一个包含文档的集合-
> db.demo10.insertOne({"StudentId":101,"StudentName":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0f68a7d7df943a7cec4f9b")
}
> db.demo10.insertOne({"StudentId":102,"StudentName":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0f68afd7df943a7cec4f9c")
}
> db.demo10.insertOne({"StudentId":103,"StudentName":"Bob"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0f68b5d7df943a7cec4f9d")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.demo10.find();
这将产生以下输出-
{ "_id" : ObjectId("5e0f68a7d7df943a7cec4f9b"), "StudentId" : 101, "StudentName" : "Chris" }
{ "_id" : ObjectId("5e0f68afd7df943a7cec4f9c"), "StudentId" : 102, "StudentName" : "David" }
{ "_id" : ObjectId("5e0f68b5d7df943a7cec4f9d"), "StudentId" : 103, "StudentName" : "Bob" }这是对单个字段的查询-
> db.demo10.find({},{"_id":0,"StudentId":0});这将产生以下输出-
{ "StudentName" : "Chris" }
{ "StudentName" : "David" }
{ "StudentName" : "Bob" }