title: Bulk update in Pymongo using multiple ObjectId
body: <p>I want to update thousands of documents in mongo collection. I want to find them using ObjectId and then whichever document matches , should be updated. My update is same for all documents. I have list of ObjectId. For every ObjectId in list, mongo should find matching document and update "isBad" key of that document to "N"</p>
  
  <pre><code>ids = [ObjectId('56ac9d3fa722f1029b75b128'), ObjectId('56ac8961a722f10249ad0ad1')]
  bulk = db.testdata.initialize_unordered_bulk_op()
  bulk.find( { '_id': ids} ).update( { '$set': {  "isBad" : "N" } } )
  print bulk.execute()
  </code></pre>
  
  <p>This gives me result :</p>
  
  <pre><code>{'nModified': 0, 'nUpserted': 0, 'nMatched': 0, 'writeErrors': [], 'upserted': [], 'writeConcernErrors': [], 'nRemoved': 0, 'nInserted': 0}
  </code></pre>
  
  <p>This is expected because it is trying to match "_id" with list. But I don't know how to proceed.</p>
  
  <p>I know how to update every document individually. My list size is of the order of 25000. I do not want to make 25000 calls individually. Number of documents in my collection are much more. I am using python2, pymongo = 3.2.1.</p>