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Brendan Whiting
Front End Web Development Techdegree Graduate 84,738 PointsWhy is one "_id" and the other "_id_"?
> db.posts.getIndexes()
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "mongoBasics.posts"
}
]
And then when I try and delete _ id _ it refers to it without the 2nd underscore as _ id:
> db.posts.dropIndex('_id_');
{
"nIndexesWas" : 1,
"ok" : 0,
"errmsg" : "cannot drop _id index",
"code" : 72
}
What's this underscore business?
1 Answer
Ken Alger
Treehouse TeacherBrendan;
Great question. As you learned, MongoDB automatically generates a field for us called _id. By default it is assigned a type of ObjectId, which is a 12-byte BSON type. Indexes are vital to performance in MongoDB and the database automatically generates an index on the _id field and assigns the index a name _id_. This is a built in index and cannot be dropped, as it sounds like you discovered. Further it's name cannot be altered because there currently is not a way to modify an index in MongoDB, they have to be dropped and recreated.
Post back if you have further questions.
Happy coding,
Ken
Brendan Whiting
Front End Web Development Techdegree Graduate 84,738 PointsBrendan Whiting
Front End Web Development Techdegree Graduate 84,738 PointsWhy does it need to give it a name _ id _ if it already is called _ id? Seems like a redundancy.
Ken Alger
Treehouse TeacherKen Alger
Treehouse Teacher_idis the field name._id_is the name of the index.Why are they named that way... because that is what the developers at MongoDB decided.
Happy coding,
Ken