cursor – Tools for iterating over MongoDB query results

Warning

This API is currently in beta, meaning the classes, methods, and behaviors described within may change before the full release. If you come across any bugs during your use of this API, please file a Jira ticket in the “Python Driver” project at https://jira.mongodb.org/browse/PYTHON.

Cursor class to iterate over Mongo query results.

class pymongo.asynchronous.cursor.AsyncCursor(collection, filter=None, projection=None, skip=0, limit=0, no_cursor_timeout=False, cursor_type=CursorType.NON_TAILABLE, sort=None, allow_partial_results=False, oplog_replay=False, batch_size=0, collation=None, hint=None, max_scan=None, max_time_ms=None, max=None, min=None, return_key=False, show_record_id=False, snapshot=False, comment=None, session=None, allow_disk_use=None)

Create a new cursor.

Should not be called directly by application developers - see find() instead.

See also

The MongoDB documentation on cursors.

Parameters:

  • collection (AsyncCollection[_DocumentType])

  • filter (Optional[Mapping[str, Any]])

  • projection (Optional[Union[Mapping[str, Any], Iterable[str]]])

  • skip (int)

  • limit (int)

  • no_cursor_timeout (bool)

  • cursor_type (int)

  • sort (Optional[_Sort])

  • allow_partial_results (bool)

  • oplog_replay (bool)

  • batch_size (int)

  • collation (Optional[_CollationIn])

  • hint (Optional[_Hint])

  • max_scan (Optional[int])

  • max_time_ms (Optional[int])

  • max (Optional[_Sort])

  • min (Optional[_Sort])

  • return_key (Optional[bool])

  • show_record_id (Optional[bool])

  • snapshot (Optional[bool])

  • comment (Optional[Any])

  • session (Optional[AsyncClientSession])

  • allow_disk_use (Optional[bool])

  • let (Optional[bool])

c[index]

See __getitem__() and read the warning.

__getitem__(index: int) → _DocumentType
__getitem__(index: slice) → AsyncCursor[_DocumentType]

Get a single document or a slice of documents from this cursor.

Warning

A AsyncCursor is not a Python list. Each index access or slice requires that a new query be run using skip and limit. Do not iterate the cursor using index accesses. The following example is extremely inefficient and may return surprising results:

cursor = db.collection.find()
# Warning: This runs a new query for each document.
# Don't do this!
for idx in range(10):
    print(cursor[idx])

Raises InvalidOperation if this cursor has already been used.

To get a single document use an integral index, e.g.:

>>> db.test.find()[50]

An IndexError will be raised if the index is negative or greater than the amount of documents in this cursor. Any limit previously applied to this cursor will be ignored.

To get a slice of documents use a slice index, e.g.:

>>> db.test.find()[20:25]

This will return this cursor with a limit of 5 and skip of 20 applied. Using a slice index will override any prior limits or skips applied to this cursor (including those applied through previous calls to this method). Raises IndexError when the slice has a step, a negative start value, or a stop value less than or equal to the start value.

Parameters:

index – An integer or slice index to be applied to this cursor

async add_option(mask)

Set arbitrary query flags using a bitmask.

To set the tailable flag: cursor.add_option(2)

Parameters:

mask (int)

Return type:

AsyncCursor[_DocumentType]

property address: tuple[str, Any] | None

The (host, port) of the server used, or None.

Changed in version 3.0: Renamed from “conn_id”.

property alive: bool

Does this cursor have the potential to return more data?

This is mostly useful with tailable cursors since they will stop iterating even though they may return more results in the future.

With regular cursors, simply use an asynchronous for loop instead of alive:

async for doc in collection.find():
    print(doc)

Note

Even if alive is True, next() can raise StopIteration. alive can also be True while iterating a cursor from a failed server. In this case alive will return False after next() fails to retrieve the next batch of results from the server.

allow_disk_use(allow_disk_use)

Specifies whether MongoDB can use temporary disk files while processing a blocking sort operation.

Raises TypeError if allow_disk_use is not a boolean.

Note

allow_disk_use requires server version >= 4.4

Parameters:

allow_disk_use (bool) – if True, MongoDB may use temporary disk files to store data exceeding the system memory limit while processing a blocking sort operation.

Return type:

AsyncCursor[_DocumentType]

Added in version 3.11.

batch_size(batch_size)

Limits the number of documents returned in one batch. Each batch requires a round trip to the server. It can be adjusted to optimize performance and limit data transfer.

Note

batch_size can not override MongoDB’s internal limits on the amount of data it will return to the client in a single batch (i.e if you set batch size to 1,000,000,000, MongoDB will currently only return 4-16MB of results per batch).

Raises TypeError if batch_size is not an integer. Raises ValueError if batch_size is less than 0. Raises InvalidOperation if this AsyncCursor has already been used. The last batch_size applied to this cursor takes precedence.

Parameters:

batch_size (int) – The size of each batch of results requested.

Return type:

AsyncCursor[_DocumentType]

clone()

Get a clone of this cursor.

Returns a new AsyncCursor instance with options matching those that have been set on the current instance. The clone will be completely unevaluated, even if the current instance has been partially or completely evaluated.

Return type:

AsyncCursor[_DocumentType]

async close()

Explicitly close / kill this cursor.

Return type:

None

collation(collation)

Adds a Collation to this query.

Raises TypeError if collation is not an instance of Collation or a dict. Raises InvalidOperation if this AsyncCursor has already been used. Only the last collation applied to this cursor has any effect.

Parameters:

collation (Optional[_CollationIn]) – An instance of Collation.

Return type:

AsyncCursor[_DocumentType]

property collection: AsyncCollection[_DocumentType]

The AsyncCollection that this AsyncCursor is iterating.

comment(comment)

Adds a ‘comment’ to the cursor.

http://mongodb.com/docs/manual/reference/operator/comment/

Parameters:

comment (Any) – A string to attach to the query to help interpret and trace the operation in the server logs and in profile data.

Return type:

AsyncCursor[_DocumentType]

Added in version 2.7.

property cursor_id: int | None

Returns the id of the cursor

Added in version 2.2.

async distinct(key)

Get a list of distinct values for key among all documents in the result set of this query.

Raises TypeError if key is not an instance of str.

The distinct() method obeys the read_preference of the AsyncCollection instance on which find() was called.

Parameters:

key (str) – name of key for which we want to get the distinct values

Return type:

list

See also

pymongo.asynchronous.collection.AsyncCollection.distinct()

async explain()

Returns an explain plan record for this cursor.

Note

This method uses the default verbosity mode of the explain command, allPlansExecution. To use a different verbosity use command() to run the explain command directly.

See also

The MongoDB documentation on explain.

Return type:

_DocumentType

hint(index)

Adds a ‘hint’, telling Mongo the proper index to use for the query.

Judicious use of hints can greatly improve query performance. When doing a query on multiple fields (at least one of which is indexed) pass the indexed field as a hint to the query. Raises OperationFailure if the provided hint requires an index that does not exist on this collection, and raises InvalidOperation if this cursor has already been used.

index should be an index as passed to create_index() (e.g. [('field', ASCENDING)]) or the name of the index. If index is None any existing hint for this query is cleared. The last hint applied to this cursor takes precedence over all others.

Parameters:

index (str | Sequence[str | Tuple[str, int | str | Mapping[str, Any]]] | Mapping[str, Any] | None) – index to hint on (as an index specifier)

Return type:

AsyncCursor[_DocumentType]

limit(limit)

Limits the number of results to be returned by this cursor.

Raises TypeError if limit is not an integer. Raises InvalidOperation if this AsyncCursor has already been used. The last limit applied to this cursor takes precedence. A limit of 0 is equivalent to no limit.

Parameters:

limit (int) – the number of results to return

Return type:

AsyncCursor[_DocumentType]

See also

The MongoDB documentation on limit.

max(spec)

Adds max operator that specifies upper bound for specific index.

When using max, hint() should also be configured to ensure the query uses the expected index and starting in MongoDB 4.2 hint() will be required.

Parameters:

spec (Sequence[str | Tuple[str, int | str | Mapping[str, Any]]] | Mapping[str, Any]) – a list of field, limit pairs specifying the exclusive upper bound for all keys of a specific index in order.

Return type:

AsyncCursor[_DocumentType]

Changed in version 3.8: Deprecated cursors that use max without a hint().

Added in version 2.7.

max_await_time_ms(max_await_time_ms)

Specifies a time limit for a getMore operation on a TAILABLE_AWAIT cursor. For all other types of cursor max_await_time_ms is ignored.

Raises TypeError if max_await_time_ms is not an integer or None. Raises InvalidOperation if this AsyncCursor has already been used.

Note

max_await_time_ms requires server version >= 3.2

Parameters:

max_await_time_ms (int | None) – the time limit after which the operation is aborted

Return type:

AsyncCursor[_DocumentType]

Added in version 3.2.

max_scan(max_scan)

DEPRECATED - Limit the number of documents to scan when performing the query.

Raises InvalidOperation if this cursor has already been used. Only the last max_scan() applied to this cursor has any effect.

Parameters:

max_scan (int | None) – the maximum number of documents to scan

Return type:

AsyncCursor[_DocumentType]

Changed in version 3.7: Deprecated max_scan(). Support for this option is deprecated in MongoDB 4.0. Use max_time_ms() instead to limit server side execution time.

max_time_ms(max_time_ms)

Specifies a time limit for a query operation. If the specified time is exceeded, the operation will be aborted and ExecutionTimeout is raised. If max_time_ms is None no limit is applied.

Raises TypeError if max_time_ms is not an integer or None. Raises InvalidOperation if this AsyncCursor has already been used.

Parameters:

max_time_ms (int | None) – the time limit after which the operation is aborted

Return type:

AsyncCursor[_DocumentType]

min(spec)

Adds min operator that specifies lower bound for specific index.

When using min, hint() should also be configured to ensure the query uses the expected index and starting in MongoDB 4.2 hint() will be required.

Parameters:

spec (Sequence[str | Tuple[str, int | str | Mapping[str, Any]]] | Mapping[str, Any]) – a list of field, limit pairs specifying the inclusive lower bound for all keys of a specific index in order.

Return type:

AsyncCursor[_DocumentType]

Changed in version 3.8: Deprecated cursors that use min without a hint().

Added in version 2.7.

async next()

Advance the cursor.

Return type:

_DocumentType

remove_option(mask)

Unset arbitrary query flags using a bitmask.

To unset the tailable flag: cursor.remove_option(2)

Parameters:

mask (int)

Return type:

AsyncCursor[_DocumentType]

property retrieved: int

The number of documents retrieved so far.

async rewind()

Rewind this cursor to its unevaluated state.

Reset this cursor if it has been partially or completely evaluated. Any options that are present on the cursor will remain in effect. Future iterating performed on this cursor will cause new queries to be sent to the server, even if the resultant data has already been retrieved by this cursor.

Return type:

AsyncCursor[_DocumentType]

property session: AsyncClientSession | None

The cursor’s AsyncClientSession, or None.

Added in version 3.6.

skip(skip)

Skips the first skip results of this cursor.

Raises TypeError if skip is not an integer. Raises ValueError if skip is less than 0. Raises InvalidOperation if this AsyncCursor has already been used. The last skip applied to this cursor takes precedence.

Parameters:

skip (int) – the number of results to skip

Return type:

AsyncCursor[_DocumentType]

sort(key_or_list, direction=None)

Sorts this cursor’s results.

Pass a field name and a direction, either ASCENDING or DESCENDING.:

async for doc in collection.find().sort('field', pymongo.ASCENDING):
    print(doc)

To sort by multiple fields, pass a list of (key, direction) pairs. If just a name is given, ASCENDING will be inferred:

async for doc in collection.find().sort([
        'field1',
        ('field2', pymongo.DESCENDING)]):
    print(doc)

Text search results can be sorted by relevance:

cursor = db.test.find(
    {'$text': {'$search': 'some words'}},
    {'score': {'$meta': 'textScore'}})

# Sort by 'score' field.
cursor.sort([('score', {'$meta': 'textScore'})])

async for doc in cursor:
    print(doc)

For more advanced text search functionality, see MongoDB’s Atlas Search.

Raises InvalidOperation if this cursor has already been used. Only the last sort() applied to this cursor has any effect.

Parameters:
Return type:

AsyncCursor[_DocumentType]

async to_list(length=None)

Converts the contents of this cursor to a list more efficiently than [doc async for doc in cursor].

To use:

>>> await cursor.to_list()

Or, so read at most n items from the cursor:

>>> await cursor.to_list(n)

If the cursor is empty or has no more results, an empty list will be returned.

Added in version 4.9.

Parameters:

length (int | None)

Return type:

list[_DocumentType]

where(code)

Adds a $where clause to this query.

The code argument must be an instance of str or Code containing a JavaScript expression. This expression will be evaluated for each document scanned. Only those documents for which the expression evaluates to true will be returned as results. The keyword this refers to the object currently being scanned. For example:

# Find all documents where field "a" is less than "b" plus "c".
async for doc in db.test.find().where('this.a < (this.b + this.c)'):
    print(doc)

Raises TypeError if code is not an instance of str. Raises InvalidOperation if this AsyncCursor has already been used. Only the last call to where() applied to a AsyncCursor has any effect.

Note

MongoDB 4.4 drops support for Code with scope variables. Consider using $expr instead.

Parameters:

code (str | Code) – JavaScript expression to use as a filter

Return type:

AsyncCursor[_DocumentType]

class pymongo.asynchronous.cursor.AsyncRawBatchCursor(collection, filter=None, projection=None, skip=0, limit=0, no_cursor_timeout=False, cursor_type=CursorType.NON_TAILABLE, sort=None, allow_partial_results=False, oplog_replay=False, batch_size=0, collation=None, hint=None, max_scan=None, max_time_ms=None, max=None, min=None, return_key=False, show_record_id=False, snapshot=False, comment=None, allow_disk_use=None)

Create a new cursor / iterator over raw batches of BSON data.

Should not be called directly by application developers - see find_raw_batches() instead.

See also

The MongoDB documentation on cursors.

Parameters: