DittoPendingCursorOperation

public class DittoPendingCursorOperation

These objects are returned when using find-like functionality on DittoCollections.

They allow chaining of further query-related functions to do things like add a limit to the number of documents you want returned or specify how you want the documents to be sorted and ordered. You can either call exec on the object to get an array of DittoDocuments as an immediate return value, or you can establish either a live query or a subscription, which both work over time.

A live query, established by calling observeLocal, will notify you every time there’s an update to a document that matches the query you provided in the preceding find-like call.

A subscription, established by calling subscribe, will act as a signal to other peers that the device connects to that you would like to receive updates from them about documents that match the query you provided in the preceding find-like call.

Typically, an app would set up a subscribe in some part of the application which is long-lived to ensure the device receives updates from the mesh. These updates will be automatically received and written into the local store. Elsewhere, where you need to use this data, an observeLocal can be used to notify you of the data, and all subsequent changes to the data.

Update and remove functionality is also exposed through this object.

  • Limit the number of documents that get returned when querying a collection for matching documents.

    Declaration

    Swift

    public func limit(_ limit: Int32) -> Self

    Parameters

    limit

    The maximum number of documents that will be returned.

    Return Value

    A DittoPendingCursorOperation that you can chain further function calls and then either get the matching documents immediately or get updates about them over time.

  • Sort the documents that match the query provided in the preceding find-like function call.

    Documents that are missing the field to sort by will appear at the beginning of the results when sorting in ascending order.

    Declaration

    Swift

    public func sort(_ query: String, direction: DittoSortDirection) -> Self

    Parameters

    query

    Name or path of the field to sort by.
    direction

    Specify whether you want the sorting order to be ascending or descending.

    Return Value

    A DittoPendingCursorOperation that you can chain further function calls and then either get the matching documents immediately or get updates about them over time.

  • Offset the resulting set of matching documents. This is useful if you aren’t interested in the first N matching documents for one reason or another. For example, you might already have queried the collection and obtained the first 20 matching documents and so you might want to run the same query as you did previously but ignore the first 20 matching documents, and that is where you would use offset.

    Declaration

    Swift

    public func offset(_ offset: UInt32) -> Self

    Parameters

    offset

    The number of matching documents that you want the eventual resulting set of matching documents to be offset by (and thus not include).

    Return Value

    A DittoPendingCursorOperation that you can chain further function calls and then either get the matching documents immediately or get updates about them over time.

  • Enables you to subscribe to changes that occur on a collection. Having a subscription acts as a signal to others that you are interested in receiving updates when local or remote changes are made to documents that match the query generated by the chain of operations that precedes the call to subscribe. The returned DittoSubscription object must be kept in scope for as long as you want to keep receiving updates.

    Declaration

    Swift

    public func subscribe() -> DittoSubscription

    Return Value

    A DittoSubscription object that must be kept in scope for as long as you want to keep receiving updates for documents that match the query specified in the preceding chain.

  • Remove all documents that match the query generated by the preceding function chaining.

    Declaration

    Swift

    @discardableResult
public func remove() -> [DittoDocumentID]

    Return Value

    A list containing the IDs of the documents that were removed.

  • Evict all documents that match the query generated by the preceding function chaining.

    Declaration

    Swift

    @discardableResult
public func evict() -> [DittoDocumentID]

    Return Value

    A list containing the IDs of the documents that were evicted.

  • Execute the query generated by the preceding function chaining and return the list of matching documents.

    Declaration

    Swift

    public func exec() -> [DittoDocument]

    Return Value

    A list of DittoDocuments matching the query generated by the preceding function chaining.

Observe

  • Enables you to listen for changes that occur on a collection. This won’t subscribe to receive changes made remotely by others and so it will only fire updates when a local change is made. If you want to receive remotely performed updates as well then also call subscribe with the relevant query. The returned DittoLiveQuery object must be kept in scope for as long as you want the provided eventHandler to be called when an update occurs.

    Declaration

    Swift

    public func observeLocal(
    deliverOn queue: DispatchQueue = .main,
    eventHandler: @escaping ([DittoDocument], DittoLiveQueryEvent) -> Void
) -> DittoLiveQuery

    Parameters

    queue

    The DispatchQueue that will be used to deliver live query updates. Defaults to DispatchQueue.main.
    eventHandler

    A closure that will be called every time there is a transaction committed to the store that involves modifications to documents matching the query in the collection that observeLocal was called on.

    Return Value

    A DittoLiveQuery object that must be kept in scope for as long as you want to keep receiving updates.

  • Enables you to listen for changes that occur on a collection, and to signal when you are ready for the live query to deliver the next event.. This won’t subscribe to receive changes made remotely by others and so it will only fire updates when a local change is made. If you want to receive remotely performed updates as well then also call subscribe with the relevant query. The returned DittoLiveQuery object must be kept in scope for as long as you want the provided eventHandler to be called when an update occurs.

    Declaration

    Swift

    public func observeLocalWithNextSignal(
    deliverOn queue: DispatchQueue = .main,
    eventHandler: @escaping ([DittoDocument], DittoLiveQueryEvent, @escaping DittoSignalNext) -> Void
) -> DittoLiveQuery

    Parameters

    queue

    The DispatchQueue that will be used to deliver live query updates. Defaults to DispatchQueue.main.
    eventHandler

    A closure that will be called every time there is a transaction committed to the store that involves modifications to documents matching the query in the collection that observeLocal was called on.

    Return Value

    A DittoLiveQuery object that must be kept in scope for as long as you want to keep receiving updates.

Update