Pymongo find document whose field is a substring of a given string - mongodb

Question

Let's say we have a collection with the following documents:
{_id : 1, str : 'hello'}
{_id : 2, str : 'hello world'}
{_id : 3, str : 'world'}
And I would like to find documents whose str field is a substring of hello world!. Is there a way to do this in pymongo?
I know the opposite - getting documents whose field contains a string can be done using $regex, but what I want is getting documents whose field is contained by a string.

Answer 1

You can use text indexes for this, which support text search queries on string content. Text indexes can include any field whose value is a string or an array of string elements.
Here's a minimal example using pymongo:
# Get database connection
conn = pymongo.MongoClient('mongodb://localhost:27017/')
coll = conn.get_database('test').get_collection('test')
# Create text index
coll.create_index([('str',pymongo.TEXT)])
# Text search
print list(coll.find({'$text': {'$search': 'hello world'}}))
With your example documents, this will result in:
[{u'_id': 3.0, u'str': u'world'},
{u'_id': 2.0, u'str': u'hello world'},
{u'_id': 1.0, u'str': u'hello'}]
For more information, please see:
Text Indexes
$text operator