Remove element from array in mongodb

Question

I am new in mongodb and i want to remove the some element in array.

my document as below

{
  "_id" : ObjectId("4d525ab2924f0000000022ad"), 
  "name" : "hello", 
  "time" : [
      {
              "stamp" : "2010-07-01T12:01:03.75+02:00",
              "reason" : "new"
      },
      {
              "stamp" : "2010-07-02T16:03:48.187+03:00",
              "reason" : "update"
      },
      {
              "stamp" : "2010-07-02T16:03:48.187+04:00",
              "reason" : "update"
      },
      {
              "stamp" : "2010-07-02T16:03:48.187+05:00",
              "reason" : "update"
      },
      {
              "stamp" : "2010-07-02T16:03:48.187+06:00",
              "reason" : "update"
      }
  ]
}

in document, i want to remove first element(reason:new) and last element(06:00) .

and i want to do it using mongoquery, i am not using any java/php driver.

Answer 1

If I'm understanding you correctly, you want to remove the first and last elements of the array if the size of the array is greater than 3. You can do this by using the findAndModify query. In mongo shell you would be using this command:

db.collection.findAndModify({
    query: { $where: "this.time.length > 3" },
    update: { $pop: {time: 1}, $pop: {time: -1} },
    new: true
});

This would find the document in your collection which matches the $where clause. The $where field allows you to specify any valid javascript method. Please note that it applies the update only to the first matched document.

You might want to look at the following docs also:

1. http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-JavascriptExpressionsand%7B%7B%24where%7D%7D for more on the $where clause.
2. http://www.mongodb.org/display/DOCS/Updating#Updating-%24pop for more on $pop.
3. http://www.mongodb.org/display/DOCS/findAndModify+Command for more on findAndModify.

Answer 2

You could update it with { $pop: { time: 1 } } to remove the last one, and { $pop: { time : -1 } } to remove the first one. There is probably a better way to handle it though.