Working with Data - The Definitive Guide to MongoDB - page 65

Setting a Field's Value
You can use the $set operator to set a field's value to one you specify. This goes for any datatype, as in the
following example:
> db.media.update ( { "Title" : "Matrix, The" }, {$set : { Genre :
"Sci-Fi" } } )
This snippet would update the genre in the document created earlier, setting it to Sci-Fi instead.
Deleting a Specified Field
The $unset operator lets you delete a given field, as in this example:
> db.media.update ( {"Title": "Matrix, The"}, {$unset : { "Genre" : 1 } } )
This snippet would delete the Genre key and its value from the document.
Appending a Value to a Specified Field
The $push operator allows you to append a value to a specified field. If the field is an existing array, then the value will
be added. If the field doesn't exist yet, then the field will be set to the array value. If the field exists, but it isn't an array,
then an error condition will be raised.
Begin by adding another author to your entry in the collection:
> db.media.update ( {"ISBN" : "978-1-4302-5821-6"}, {$push: { Author : "Griffin,
Stewie"} } )
The next snippet raises an error message because the Title field is not an array:
> db.media.update ( {"ISBN" : "978-1-4302-5821-6"}, {$push: { Title :
"This isn't an array"} } )
Cannot apply $push/$pushAll modifier to non-array
The following example shows how the document looks in the meantime:
> db.media.find ( { "ISBN" : "978-1-4302-5821-6" } )
{
"Author" :
[
"Hows, David",
"Membrey, Peter",
"Plugge, Eelco",
"Griffin, Stewie",
],
"ISBN" : "978-1-4302-5821-6",
"Publisher" : "Apress",
"Title" : "Definitive Guide to MongoDB 2nd ed., The",
"Type" : "Book",
"_id" : ObjectId("4c436231c603000000007ed0")
}