I'm trying to obtain explain from quite simple query. It uses posts collection with following schema:
> db.posts.findOne()
{
"_id" : ObjectId("55236e6182bf196454a952b6"),
"Content" : "wuOfCjKborHcxkoyXzXiW",
"CreatedAtUtc" : ISODate("2014-01-18T23:59:30.023Z"),
"Tags" : [
"sjM",
"Van",
"Orm"
],
"Title" : "msAQAbQwAl",
"Author" : "yIIhato",
"Comments" : [ ]
}
Query I want to explain is this:
db.posts.find( { $query: {}, $orderby: { "CreatedAtUtc" : -1 } } )
It produces proper result without any errors. But it throws the exception when I want to explain it. I've tried these commands to explain query:
db.posts.explain().find( { $query: {}, $orderby: { "CreatedAtUtc" : -1 } } )
db.posts.find( { $query: {}, $orderby: { "CreatedAtUtc" : -1 } } ).explain()
var cursor = db.posts.find( { $query: {}, $orderby: { "CreatedAtUtc" : -1 } } )
cursor.explain()
The error is always the same:
2015-11-08T16:20:40.137+0100 E QUERY Error: explain failed: { "ok" : 0, "errm
sg" : "unknown top level operator: $query", "code" : 2 }
at Error (<anonymous>)
at Function.throwOrReturn (src/mongo/shell/explainable.js:34:19)
at constructor.finish (src/mongo/shell/explain_query.js:188:36)
at DBQuery.explain (src/mongo/shell/query.js:434:25)
at (shell):1:8 at src/mongo/shell/explainable.js:34
>
From the docs:
Do not mix query forms. If you use the
$query
format, do not append cursor methods to thefind()
. To modify the query use the meta-query operators, such as$explain
.Therefore, the following two operations are equivalent:
db.collection.find( { $query: { age : 25 }, $explain: true } )
db.collection.find( { age : 25 } ).explain()
So in your case, as the $explain
operator has been deprecated since version 3.0, use the latter form of querying like:
db.posts.find({}).sort({ "CreatedAtUtc" : -1 }).explain();