Updating documents has a similar interface with the ->updateOne() OR ->updateMany() method.
The first parameter is the query used to find documents and the second one will update our documents.
We can use any of the update operators explained at the end of this chapter to update in place or specify a new document to completely replace the document in the query:
$result = $collection->updateOne(
array( "isbn" => "401"),
array( '$set' => array( "price" => 39 ) )
);
We can use single quotes or double quotes for key names, but if we have special operators starting with $, we need to use single quotes. We can use array( "key" => "value" ) or ["key" => "value"]. We prefer the more explicit array() notation in this book.
The ->getMatchedCount() and ->getModifiedCount() methods will return the number of documents matched in the query part or the ones modified from the query. If the new value is the same as the existing value of a document, it will not be counted as modified.