如何使用2.4 C＃Mongo驱动程序运行解释查询？

Question

A long time ago using an older version of the Mongo C# driver, it was possible to do something along the lines of this (I forget exactly).

collection.FindOne(query).Explain()

And this would provide details of query execution, indexes used, etc. using cursor.explain() . Now we're using 2.4 and would like to use explain for one of our queries.

The only question I found relating to this was this one but the driver used seems to be different again.

How do I run an explain query with the 2.4 C# driver?

Answer 1

According to an issue on MongoDB's JIRA page, it was removed from the API as an out of the box feature.

Explain is/has undergone some changes and adding it to the driver before that is done would have been a mistake. In addition, we feel that most explanations happen in the shell and not in the drivers. As a result, we've not included explain as part of the API.

Fortunately, it's still possible by supplying the query modifier in FindOptions :

var options = new FindOptions
{
    Modifiers = new BsonDocument("$explain", true)
};
var explain = await collection.Find(x => true, options)
    .Project(new BsonDocument())
    .FirstOrDefault()
    ?.ToJson();

Simply replace x => true with the query you would like to profile. I've added .ToJson() in order to get a nice human-readable JSON string.