[−][src]Struct mongodb::Cursor
A Cursor
streams the result of a query. When a query is made, a Cursor
will be returned with
the first batch of results from the server; the documents will be returned as the Cursor
is
iterated. When the batch is exhausted and if there are more results, the Cursor
will fetch the
next batch of documents, and so forth until the results are exhausted. Note that because of this
batching, additional network I/O may occur on any given call to Cursor::next
. Because of this,
a Cursor
iterates over Result<Document>
items rather than simply Document
items.
The batch size of the Cursor
can be configured using the options to the method that returns
it. For example, setting the batch_size
field of
FindOptions
will set the batch size of the
Cursor
returned by Collection::find
.
Note that the batch size determines both the number of documents stored in memory by the
Cursor
at a given time as well as the total number of network round-trips needed to fetch all
results from the server; both of these factors should be taken into account when choosing the
optimal batch size.
A cursor can be used like any other Stream
. The simplest way is just to iterate over the
documents it yields:
while let Some(doc) = cursor.next().await { println!("{}", doc?) }
Additionally, all the other methods that an Stream
has are available on Cursor
as well.
This includes all of the functionality provided by StreamExt
, which provides similar functionality to the standard library Iterator
trait.
For instance, if the number of results from a query is known to be small, it might make sense
to collect them into a vector:
let results: Vec<Result<Document>> = cursor.collect().await;
Trait Implementations
Auto Trait Implementations
impl !RefUnwindSafe for Cursor
impl Send for Cursor
impl !Sync for Cursor
impl Unpin for Cursor
impl !UnwindSafe for Cursor
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T> Same<T> for T
type Output = T
Should always be Self
impl<T> StreamExt for T where
T: Stream + ?Sized,
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T: Stream + ?Sized,
fn next(&mut self) -> Next<Self> where
Self: Unpin,
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Self: Unpin,
fn into_future(self) -> StreamFuture<Self> where
Self: Unpin,
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Self: Unpin,
fn map<T, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> T,
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F: FnMut(Self::Item) -> T,
fn enumerate(self) -> Enumerate<Self>
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fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F> where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
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F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = Option<T>>,
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F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = Option<T>>,
fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future,
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F: FnMut(Self::Item) -> Fut,
Fut: Future,
fn collect<C>(self) -> Collect<Self, C> where
C: Default + Extend<Self::Item>,
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C: Default + Extend<Self::Item>,
fn concat(self) -> Concat<Self> where
Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
Self::Item: IntoIterator,
Self::Item: Default,
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Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
Self::Item: IntoIterator,
Self::Item: Default,
fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F> where
F: FnMut(T, Self::Item) -> Fut,
Fut: Future<Output = T>,
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F: FnMut(T, Self::Item) -> Fut,
Fut: Future<Output = T>,
fn flatten(self) -> Flatten<Self> where
Self::Item: Stream,
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Self::Item: Stream,
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where
F: FnMut(Self::Item) -> U,
U: Stream,
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F: FnMut(Self::Item) -> U,
U: Stream,
fn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F> where
F: FnMut(&mut S, Self::Item) -> Fut,
Fut: Future<Output = Option<B>>,
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F: FnMut(&mut S, Self::Item) -> Fut,
Fut: Future<Output = Option<B>>,
fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F> where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
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F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F> where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
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F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut> where
Fut: Future,
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Fut: Future,
fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
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F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
fn for_each_concurrent<Fut, F>(
self,
limit: impl Into<Option<usize>>,
f: F
) -> ForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
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self,
limit: impl Into<Option<usize>>,
f: F
) -> ForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
fn take(self, n: usize) -> Take<Self>
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fn skip(self, n: usize) -> Skip<Self>
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fn fuse(self) -> Fuse<Self>
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fn by_ref(&mut self) -> &mut Self
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fn catch_unwind(self) -> CatchUnwind<Self> where
Self: UnwindSafe,
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Self: UnwindSafe,
fn boxed<'a>(self) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a + Send>> where
Self: Send + 'a,
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Self: Send + 'a,
fn boxed_local<'a>(self) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a>> where
Self: 'a,
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Self: 'a,
fn buffered(self, n: usize) -> Buffered<Self> where
Self::Item: Future,
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Self::Item: Future,
fn buffer_unordered(self, n: usize) -> BufferUnordered<Self> where
Self::Item: Future,
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Self::Item: Future,
fn zip<St>(self, other: St) -> Zip<Self, St> where
St: Stream,
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St: Stream,
fn chain<St>(self, other: St) -> Chain<Self, St> where
St: Stream<Item = Self::Item>,
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St: Stream<Item = Self::Item>,
fn peekable(self) -> Peekable<Self>
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fn chunks(self, capacity: usize) -> Chunks<Self>
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fn ready_chunks(self, capacity: usize) -> ReadyChunks<Self>
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fn forward<S>(self, sink: S) -> Forward<Self, S> where
S: Sink<Self::Ok, Error = Self::Error>,
Self: TryStream,
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S: Sink<Self::Ok, Error = Self::Error>,
Self: TryStream,
fn split<Item>(self) -> (SplitSink<Self, Item>, SplitStream<Self>) where
Self: Sink<Item>,
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Self: Sink<Item>,
fn inspect<F>(self, f: F) -> Inspect<Self, F> where
F: FnMut(&Self::Item),
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F: FnMut(&Self::Item),
fn left_stream<B>(self) -> Either<Self, B> where
B: Stream<Item = Self::Item>,
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B: Stream<Item = Self::Item>,
fn right_stream<B>(self) -> Either<B, Self> where
B: Stream<Item = Self::Item>,
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B: Stream<Item = Self::Item>,
fn poll_next_unpin(&mut self, cx: &mut Context) -> Poll<Option<Self::Item>> where
Self: Unpin,
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Self: Unpin,
fn select_next_some(&mut self) -> SelectNextSome<Self> where
Self: Unpin + FusedStream,
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Self: Unpin + FusedStream,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<S, T, E> TryStream for S where
S: Stream<Item = Result<T, E>> + ?Sized,
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S: Stream<Item = Result<T, E>> + ?Sized,
type Ok = T
The type of successful values yielded by this future
type Error = E
The type of failures yielded by this future
fn try_poll_next(
self: Pin<&mut S>,
cx: &mut Context
) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>
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self: Pin<&mut S>,
cx: &mut Context
) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>
impl<S> TryStreamExt for S where
S: TryStream + ?Sized,
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S: TryStream + ?Sized,
fn err_into<E>(self) -> ErrInto<Self, E> where
Self::Error: Into<E>,
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Self::Error: Into<E>,
fn map_ok<T, F>(self, f: F) -> MapOk<Self, F> where
F: FnMut(Self::Ok) -> T,
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F: FnMut(Self::Ok) -> T,
fn map_err<E, F>(self, f: F) -> MapErr<Self, F> where
F: FnMut(Self::Error) -> E,
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F: FnMut(Self::Error) -> E,
fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
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F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F> where
F: FnMut(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
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F: FnMut(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F> where
F: FnMut(&Self::Ok),
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F: FnMut(&Self::Ok),
fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where
F: FnMut(&Self::Error),
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F: FnMut(&Self::Error),
fn into_stream(self) -> IntoStream<Self>
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fn try_next(&mut self) -> TryNext<Self> where
Self: Unpin,
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Self: Unpin,
fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
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F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
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F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
fn try_for_each_concurrent<Fut, F>(
self,
limit: impl Into<Option<usize>>,
f: F
) -> TryForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = Result<(), Self::Error>>,
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self,
limit: impl Into<Option<usize>>,
f: F
) -> TryForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = Result<(), Self::Error>>,
fn try_collect<C>(self) -> TryCollect<Self, C> where
C: Default + Extend<Self::Ok>,
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C: Default + Extend<Self::Ok>,
fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: Future<Output = bool>,
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F: FnMut(&Self::Ok) -> Fut,
Fut: Future<Output = bool>,
fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
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F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
fn try_flatten(self) -> TryFlatten<Self> where
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
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Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F> where
F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
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F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
fn try_concat(self) -> TryConcat<Self> where
Self::Ok: Extend<<Self::Ok as IntoIterator>::Item>,
Self::Ok: IntoIterator,
Self::Ok: Default,
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Self::Ok: Extend<<Self::Ok as IntoIterator>::Item>,
Self::Ok: IntoIterator,
Self::Ok: Default,
fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self> where
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
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Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
fn try_poll_next_unpin(
&mut self,
cx: &mut Context
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,
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&mut self,
cx: &mut Context
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,
fn into_async_read(self) -> IntoAsyncRead<Self> where
Self: TryStreamExt<Error = Error> + Unpin,
Self::Ok: AsRef<[u8]>,
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Self: TryStreamExt<Error = Error> + Unpin,
Self::Ok: AsRef<[u8]>,
impl<V, T> VZip<V> for T where
V: MultiLane<T>,
V: MultiLane<T>,