cursor.hpp

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#pragma once
 
/// @file userver/storages/mongo/cursor.hpp
/// @brief @copybrief storages::mongo::Cursor
 
#include <iterator>
#include <memory>
 
#include <userver/formats/bson/document.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace storages::mongo {
namespace impl {
class CursorImpl;
}  // namespace impl
 
/// Interface for MongoDB query cursors
class Cursor {
public:
    explicit Cursor(std::unique_ptr<impl::CursorImpl>&&);
    ~Cursor();
 
    Cursor(Cursor&&) noexcept;
    Cursor& operator=(Cursor&&) noexcept;
 
    class Iterator {
    public:
        using iterator_category = std::input_iterator_tag;
        using difference_type = ptrdiff_t;
        using value_type = formats::bson::Document;
        using reference = const value_type&;
        using pointer = const value_type*;
 
        explicit Iterator() = default;
        explicit Iterator(Cursor*);
 
        class DocHolder {
        public:
            explicit DocHolder(value_type doc)
                : doc_(std::move(doc))
            {}
 
            value_type& operator*() { return doc_; }
 
        private:
            value_type doc_;
        };
        DocHolder operator++(int);
        Iterator& operator++();
        reference operator*() const;
        pointer operator->() const;
 
        bool operator==(const Iterator&) const;
        bool operator!=(const Iterator&) const;
 
    private:
        Cursor* cursor_;
    };
 
    bool HasMore() const;
    explicit operator bool() const { return HasMore(); }
 
    /// Retrieve the cursor batch size; returns zero if the cursor uses the server-defined maximum batch size.
    std::uint32_t GetBatchSize() const;
 
    /// Set the cursor batch size; set to zero to force the cursor to use the server-defined maximum batch size.
    void SetBatchSize(std::uint32_t);
 
    Iterator begin();
    Iterator end();
 
private:
    std::unique_ptr<impl::CursorImpl> impl_;
};
 
}  // namespace storages::mongo
 
USERVER_NAMESPACE_END