MongoDB查询选择并仅显示文档中的特定字段？
首先让我们创建一个包含文档的集合-
> db.querySelectDemo.insertOne({UserId:100,UserName:"Chris",UserAge:25});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ce90eb478f00858fb12e90e")
}
> db.querySelectDemo.insertOne({UserId:101,UserName:"Robert",UserAge:26});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ce90ec578f00858fb12e90f")
}
> db.querySelectDemo.insertOne({UserId:103,UserName:"David",UserAge:27});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ce90ed478f00858fb12e910")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.querySelectDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5ce90eb478f00858fb12e90e"),
"UserId" : 100,
"UserName" : "Chris",
"UserAge" : 25
}
{
"_id" : ObjectId("5ce90ec578f00858fb12e90f"),
"UserId" : 101,
"UserName" : "Robert",
"UserAge" : 26
}
{
"_id" : ObjectId("5ce90ed478f00858fb12e910"),
"UserId" : 103,
"UserName" : "David",
"UserAge" : 27
}以下是通过在find()−中将其设置为TRUE来仅包含特定字段的查询
> db.querySelectDemo.find({},{_id:0,UserName:true});这将产生以下输出-
{ "UserName" : "Chris" }
{ "UserName" : "Robert" }
{ "UserName" : "David" }