Removing data

Important note: This article is in relation to online MongoDB course. For more information about the course and other posts describing its content please check my main page here: M101P: MongoDB for Developers course. 

 
> db.arrays.find()
{ "_id" : ObjectId("52ba1c78a83c1ee5e6c903a1"), "a" : 2, "tab" : [  11,  22,  "hello" ] }
{ "_id" : ObjectId("52ba1e4cc1207a4a1fdeb3ac"), "a" : 3, "tab" : { "2" : "london" } }
{ "_id" : ObjectId("52ba1e99c1207a4a1fdeb3ad"), "a" : 4, "mystr" : "poland" }
>
> db.arrays.remove( { a: 2})
> db.arrays.find()
{ "_id" : ObjectId("52ba1e4cc1207a4a1fdeb3ac"), "a" : 3, "tab" : { "2" : "london" } }
{ "_id" : ObjectId("52ba1e99c1207a4a1fdeb3ad"), "a" : 4, "mystr" : "poland" }

This removes all the documents in the collection at once. The drop method is more recommended because it drops the whole collection instead or removing document by document (more performant).

 
> db.arrays.remove()
> db.arrays.drop()
> db.arrays.find()

IMPORTANT: multi document operation are not atomic and the db engine execution thread after removing a few documents can yield the execution to another thread before returning and finishing its operation.