MongoDB将字段和切片投影限制在一起？
使用$slice运算符。首先让我们创建一个包含文档的集合-
> db.limitAndSliceProjectionDemo.insertOne(
{
"_id" : 101,
"UserName" : "Carol",
"UserAge" : 26,
"UserMesssage" : [
"Hi",
"Hello",
"Bye",
"Awesome",
"Good",
"Bad",
"Nice",
"Good Night",
"Good Morning"
]
}
);
{ "acknowledged" : true, "insertedId" : 101 }以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.limitAndSliceProjectionDemo.find().pretty();
这将产生以下输出-
{
"_id" : 101,
"UserName" : "Carol",
"UserAge" : 26,
"UserMesssage" : [
"Hi",
"Hello",
"Bye",
"Awesome",
"Good",
"Bad",
"Nice",
"Good Night",
"Good Morning"
]
}以下是限制字段并一起执行切片投影的查询。在这里，我们从2切成4-
> db.limitAndSliceProjectionDemo.find({ "UserName" : "Carol" }, {"_id": 0, "UserName":0,"UserAge":0, "UserMesssage": { "$slice": [2,4] } }).pretty();这将产生以下输出-
{ "UserMesssage" : [ "Bye", "Awesome", "Good", "Bad" ] }