result_set.hpp

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#pragma once
 
/// @file userver/storages/postgres/result_set.hpp
/// @brief Result accessors
 
#include <initializer_list>
#include <limits>
#include <memory>
#include <optional>
#include <tuple>
#include <type_traits>
#include <utility>
#include <variant>
 
#include <fmt/format.h>
 
#include <userver/storages/postgres/exceptions.hpp>
#include <userver/storages/postgres/io/supported_types.hpp>
#include <userver/storages/postgres/postgres_fwd.hpp>
 
#include <userver/storages/postgres/detail/const_data_iterator.hpp>
 
#include <userver/compiler/demangle.hpp>
#include <userver/logging/log.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace storages::postgres {
 
/// @page pg_process_results uPg: Working with result sets
///
/// A result set returned from Execute function is a thin read only wrapper
/// around the libpq result. It can be copied around as it contains only a
/// smart pointer to the underlying result set.
///
/// The result set's lifetime is not limited by the transaction in which it was
/// created. In can be used after the transaction is committed or rolled back.
///
/// @par Iterating result set's rows
///
/// The ResultSet provides interface for range-based iteration over its rows.
/// @code
/// auto result = trx.Execute("select foo, bar from foobar");
/// for (auto row : result) {
///   // Process row data here
/// }
/// @endcode
///
/// Also rows can be accessed via indexing operators.
/// @code
/// auto result = trx.Execute("select foo, bar from foobar");
/// for (auto idx = 0; idx < result.Size(); ++idx) {
///   auto row = result[idx];
///   // process row data here
/// }
/// @endcode
///
/// @par Accessing fields in a row
///
/// Fields in a row can be accessed by their index, by field name and can be
/// iterated over. Invalid index or name will throw an exception.
/// @code
/// auto f1 = row[0];
/// auto f2 = row["foo"];
/// auto f3 = row[1];
/// auto f4 = row["bar"];
///
/// for (auto f : row) {
///   // Process field here
/// }
/// @endcode
///
/// @par Extracting field's data to variables
///
/// A Field object provides an interface to convert underlying buffer to a
/// C++ variable of supported type. Please see
/// @ref scripts/docs/en/userver/pg_types.md for more information on supported
/// types.
///
/// Functions Field::As and Field::To can throw an exception if the field
/// value is `null`. Their Field::Coalesce counterparts instead set the result
/// to default value.
///
/// All data extraction functions can throw parsing errors (descendants of
/// ResultSetError).
///
/// @code
/// auto foo = row["foo"].As<int>();
/// auto bar = row["bar"].As<std::string>();
///
/// foo = row["foo"].Coalesce(42);
/// // There is no parser for char*, so a string object must be passed here.
/// bar = row["bar"].Coalesce(std::string{"bar"});
///
/// row["foo"].To(foo);
/// row["bar"].To(bar);
///
/// row["foo"].Coalesce(foo, 42);
/// // The type is deduced by the first argument, so the second will be also
/// // treated as std::string
/// row["bar"].Coalesce(bar, "baz");
/// @endcode
///
/// @par Extracting data directly from a Row object
///
/// Data can be extracted straight from a Row object to a pack or a tuple of
/// user variables. The number of user variables cannot exceed the number of
/// fields in the result. If it does, an exception will be thrown.
///
/// When used without additional parameters, the field values are extracted
/// in the order of their appearance.
///
/// When a subset of the fields is needed, the fields can be specified by their
/// indexes or names.
///
/// Row's data extraction functions throw exceptions as the field extraction
/// functions. Also a FieldIndexOutOfBounds or FieldNameDoesntExist can be
/// thrown.
///
/// Statements that return user-defined PostgreSQL type may be called as
/// returning either one-column row with the whole type in it or as multi-column
/// row with every column representing a field in the type. For the purpose of
/// disambiguation, kRowTag may be used.
///
/// When a first column is extracted, it is expected that the result set
/// contains the only column, otherwise an exception will be thrown.
///
/// @code
/// auto [foo, bar] = row.As<int, std::string>();
/// row.To(foo, bar);
///
/// auto [bar, foo] = row.As<std::string, int>({1, 0});
/// row.To({1, 0}, bar, foo);
///
/// auto [bar, foo] = row.As<std::string, int>({"bar", "foo"});
/// row.To({"bar", "foo"}, bar, foo);
///
/// // extract the whole row into a row-type structure.
/// // The FooBar type must not have the C++ to PostgreSQL mapping in this case
/// auto foobar = row.As<FooBar>();
/// row.To(foobar);
/// // If the FooBar type does have the mapping, the function call must be
/// // disambiguated.
/// foobar = row.As<FooBar>(kRowTag);
/// row.To(foobar, kRowTag);
/// @endcode
///
/// In the following example it is assumed that the row has a single column
/// and the FooBar type is mapped to a PostgreSQL type.
///
/// @note The row is used to extract different types, it doesn't mean it will
/// actually work with incompatible types.
///
/// @code
/// auto foobar = row.As<FooBar>();
/// row.To(foobar);
///
/// auto str = row.As<std::string>();
/// auto i = row.As<int>();
/// @endcode
///
///
/// @par Converting a Row to a user row type
///
/// A row can be converted to a user type (tuple, structure, class), for more
/// information on data type requirements see @ref pg_user_row_types
///
/// @todo Interface for converting rows to arbitrary user types
///
/// @par Converting ResultSet to a result set with user row types
///
/// A result set can be represented as a set of user row types or extracted to
/// a container. For more information see @ref pg_user_row_types
///
/// @todo Interface for copying a ResultSet to an output iterator.
///
/// @par Non-select query results
///
/// @todo Process non-select result and provide interface. Do the docs.
///
///
/// ----------
///
/// @htmlonly <div class="bottom-nav"> @endhtmlonly
/// ⇦ @ref pg_run_queries | @ref scripts/docs/en/userver/pg_types.md ⇨
/// @htmlonly </div> @endhtmlonly
 
struct FieldDescription {
    /// Index of the field in the result set
    std::size_t index;
    /// @brief The object ID of the field's data type.
    Oid type_oid;
    /// @brief The field name.
    // TODO string_view
    std::string name;
    /// @brief If the field can be identified as a column of a specific table,
    /// the object ID of the table; otherwise zero.
    Oid table_oid;
    /// @brief If the field can be identified as a column of a specific table,
    /// the attribute number of the column; otherwise zero.
    Integer table_column;
    /// @brief The data type size (see pg_type.typlen). Note that negative
    /// values denote variable-width types.
    Integer type_size;
    /// @brief The type modifier (see pg_attribute.atttypmod). The meaning of
    /// the modifier is type-specific.
    Integer type_modifier;
};
 
/// @brief A wrapper for PGresult to access field descriptions.
class RowDescription {
public:
    RowDescription(detail::ResultWrapperPtr res) : res_{std::move(res)} {}
 
    /// Check that all fields can be read in binary format
    /// @throw NoBinaryParser if any of the fields doesn't have a binary parser
    void CheckBinaryFormat(const UserTypes& types) const;
 
    // TODO interface for iterating field descriptions
private:
    detail::ResultWrapperPtr res_;
};
 
class Row;
class ResultSet;
template <typename T, typename ExtractionTag>
class TypedResultSet;
 
class FieldView final {
public:
    using size_type = std::size_t;
 
    FieldView(const detail::ResultWrapper& res, size_type row_index, size_type field_index)
        : res_{res}, row_index_{row_index}, field_index_{field_index} {}
 
    template <typename T>
    size_type To(T&& val) const {
        using ValueType = typename std::decay<T>::type;
        auto fb = GetBuffer();
        return ReadNullable(fb, std::forward<T>(val), io::traits::IsNullable<ValueType>{});
    }
 
private:
    io::FieldBuffer GetBuffer() const;
    std::string_view Name() const;
    Oid GetTypeOid() const;
    const io::TypeBufferCategory& GetTypeBufferCategories() const;
 
    template <typename T>
    size_type ReadNullable(const io::FieldBuffer& fb, T&& val, std::true_type) const {
        using ValueType = typename std::decay<T>::type;
        using NullSetter = io::traits::GetSetNull<ValueType>;
        if (fb.is_null) {
            NullSetter::SetNull(val);
        } else {
            Read(fb, std::forward<T>(val));
        }
        return fb.length;
    }
 
    template <typename T>
    size_type ReadNullable(const io::FieldBuffer& buffer, T&& val, std::false_type) const {
        if (buffer.is_null) {
            throw FieldValueIsNull{field_index_, Name(), val};
        } else {
            Read(buffer, std::forward<T>(val));
        }
        return buffer.length;
    }
 
    template <typename T>
    void Read(const io::FieldBuffer& buffer, T&& val) const {
        using ValueType = typename std::decay<T>::type;
        io::traits::CheckParser<ValueType>();
        try {
            io::ReadBuffer(buffer, std::forward<T>(val), GetTypeBufferCategories());
        } catch (InvalidInputBufferSize& ex) {
            // InvalidInputBufferSize is not descriptive. Enriching with OID information and C++ types info
            ex.AddMsgPrefix(fmt::format(
                "Error while reading field #{0} '{1}' which database type {2} as a C++ type '{3}'. Refer to "
                "the 'Supported data types' in the documentation to make sure that the database type is actually "
                "representable as a C++ type '{3}'. Error details: ",
                field_index_,
                Name(),
                impl::OidPrettyPrint(GetTypeOid()),
                compiler::GetTypeName<T>()
            ));
            UASSERT_MSG(false, ex.what());
            throw;
        } catch (ResultSetError& ex) {
            ex.AddMsgSuffix(fmt::format(" (ResultSet error while reading field #{} name `{}`)", field_index_, Name()));
            throw;
        }
    }
 
    const detail::ResultWrapper& res_;
    const size_type row_index_;
    const size_type field_index_;
};
 
/// @brief Accessor to a single field in a result set's row
class Field {
public:
    using size_type = std::size_t;
 
    size_type RowIndex() const { return row_index_; }
    size_type FieldIndex() const { return field_index_; }
 
    //@{
    /** @name Field metadata */
    /// Field name as named in query
    std::string_view Name() const;
    FieldDescription Description() const;
 
    Oid GetTypeOid() const;
    //@}
 
    //@{
    /** @name Data access */
    bool IsNull() const;
 
    /// Read the field's buffer into user-provided variable.
    /// @throws FieldValueIsNull If the field is null and the C++ type is
    ///                           not nullable.
    template <typename T>
    size_type To(T&& val) const {
        return FieldView{*res_, row_index_, field_index_}.To(std::forward<T>(val));
    }
 
    /// Read the field's buffer into user-provided variable.
    /// If the field is null, set the variable to the default value.
    template <typename T>
    void Coalesce(T& val, const T& default_val) const {
        if (!IsNull())
            To(val);
        else
            val = default_val;
    }
 
    /// Convert the field's buffer into a C++ type.
    /// @throws FieldValueIsNull If the field is null and the C++ type is
    ///                           not nullable.
    template <typename T>
    typename std::decay<T>::type As() const {
        T val{};
        To(val);
        return val;
    }
 
    /// Convert the field's buffer into a C++ type.
    /// If the field is null, return default value.
    template <typename T>
    typename std::decay<T>::type Coalesce(const T& default_val) const {
        if (IsNull()) return default_val;
        return As<T>();
    }
    //@}
    const io::TypeBufferCategory& GetTypeBufferCategories() const;
 
protected:
    friend class Row;
 
    Field() = default;
 
    Field(detail::ResultWrapperPtr res, size_type row, size_type col)
        : res_{std::move(res)}, row_index_{row}, field_index_{col} {}
 
    //@{
    /** @name Iteration support */
    bool IsValid() const;
    int Compare(const Field& rhs) const;
    std::ptrdiff_t Distance(const Field& rhs) const;
    Field& Advance(std::ptrdiff_t);
    //@}
 
private:
    detail::ResultWrapperPtr res_;
    size_type row_index_{0};
    size_type field_index_{0};
};
 
/// @brief Iterator over fields in a result set's row
class ConstFieldIterator
    : public detail::ConstDataIterator<ConstFieldIterator, Field, detail::IteratorDirection::kForward> {
public:
    ConstFieldIterator() = default;
 
private:
    friend class Row;
 
    ConstFieldIterator(detail::ResultWrapperPtr res, size_type row, size_type col)
        : ConstDataIterator(std::move(res), row, col) {}
};
 
/// @brief Reverse iterator over fields in a result set's row
class ReverseConstFieldIterator
    : public detail::ConstDataIterator<ReverseConstFieldIterator, Field, detail::IteratorDirection::kReverse> {
public:
    ReverseConstFieldIterator() = default;
 
private:
    friend class Row;
 
    ReverseConstFieldIterator(detail::ResultWrapperPtr res, size_type row, size_type col)
        : ConstDataIterator(std::move(res), row, col) {}
};
 
/// Data row in a result set
/// This class is a mere accessor to underlying result set data buffer,
/// must not be used outside of result set life scope.
///
/// Mimics field container
class Row {
public:
    //@{
    /** @name Field container concept */
    using size_type = std::size_t;
    using const_iterator = ConstFieldIterator;
    using const_reverse_iterator = ReverseConstFieldIterator;
 
    using value_type = Field;
    using reference = Field;
    using pointer = const_iterator;
    //@}
 
    size_type RowIndex() const { return row_index_; }
 
    RowDescription GetDescription() const { return {res_}; }
    //@{
    /** @name Field container interface */
    /// Number of fields
    size_type Size() const;
 
    //@{
    /** @name Forward iteration */
    const_iterator cbegin() const;
    const_iterator begin() const { return cbegin(); }
    const_iterator cend() const;
    const_iterator end() const { return cend(); }
    //@}
    //@{
    /** @name Reverse iteration */
    const_reverse_iterator crbegin() const;
    const_reverse_iterator rbegin() const { return crbegin(); }
    const_reverse_iterator crend() const;
    const_reverse_iterator rend() const { return crend(); }
    //@}
 
    /// @brief Field access by index
    /// @throws FieldIndexOutOfBounds if index is out of bounds
    reference operator[](size_type index) const;
    /// @brief Field access field by name
    /// @throws FieldNameDoesntExist if the result set doesn't contain
    ///         such a field
    reference operator[](const std::string& name) const;
    //@}
 
    //@{
    /** @name Access to row's data */
    /// Read the contents of the row to a user's row type or read the first
    /// column into the value.
    ///
    /// If the user tries to read the first column into a variable, it must be the
    /// only column in the result set. If the result set contains more than one
    /// column, the function will throw NonSingleColumnResultSet. If the result
    /// set is OK to contain more than one columns, the first column value should
    /// be accessed via `row[0].To/As`.
    ///
    /// If the type is a 'row' type, the function will read the fields of the row
    /// into the type's data members.
    ///
    /// If the type can be treated as both a row type and a composite type (the
    /// type is mapped to a PostgreSQL type), the function will treat the type
    /// as a type for the first (and the only) column.
    ///
    /// To read the all fields of the row as a row type, the To(T&&, RowTag)
    /// should be used.
    template <typename T>
    void To(T&& val) const;
 
    /// Function to disambiguate reading the row to a user's row type (values
    /// of the row initialize user's type data members)
    template <typename T>
    void To(T&& val, RowTag) const;
 
    /// Function to disambiguate reading the first column to a user's composite
    /// type (PostgreSQL composite type in the row initializes user's type).
    /// The same as calling To(T&& val) for a T mapped to a PostgreSQL type.
    template <typename T>
    void To(T&& val, FieldTag) const;
 
    /// Read fields into variables in order of their appearance in the row
    template <typename... T>
    void To(T&&... val) const;
 
    /// @brief Parse values from the row and return the result.
    ///
    /// If there are more than one type arguments to the function, it will
    /// return a tuple of those types.
    ///
    /// If there is a single type argument to the function, it will read the first
    /// and the only column of the row or the whole row to the row type (depending
    /// on C++ to PosgreSQL mapping presence) and return plain value of this type.
    ///
    /// @see To(T&&)
    template <typename T, typename... Y>
    auto As() const;
 
    /// @brief Returns T initialized with values of the row.
    /// @snippet storages/postgres/tests/typed_rows_pgtest.cpp RowTagSippet
    template <typename T>
    T As(RowTag) const {
        T val{};
        To(val, kRowTag);
        return val;
    }
 
    /// @brief Returns T initialized with a single column value of the row.
    /// @snippet storages/postgres/tests/composite_types_pgtest.cpp FieldTagSippet
    template <typename T>
    T As(FieldTag) const {
        T val{};
        To(val, kFieldTag);
        return val;
    }
 
    /// Read fields into variables in order of their names in the first argument
    template <typename... T>
    void To(const std::initializer_list<std::string>& names, T&&... val) const;
    template <typename... T>
    std::tuple<T...> As(const std::initializer_list<std::string>& names) const;
 
    /// Read fields into variables in order of their indexes in the first
    /// argument
    template <typename... T>
    void To(const std::initializer_list<size_type>& indexes, T&&... val) const;
    template <typename... T>
    std::tuple<T...> As(const std::initializer_list<size_type>& indexes) const;
    //@}
 
    size_type IndexOfName(const std::string&) const;
 
    FieldView GetFieldView(size_type index) const;
 
protected:
    friend class ResultSet;
 
    Row() = default;
 
    Row(detail::ResultWrapperPtr res, size_type row) : res_{std::move(res)}, row_index_{row} {}
 
    //@{
    /** @name Iteration support */
    bool IsValid() const;
    int Compare(const Row& rhs) const;
    std::ptrdiff_t Distance(const Row& rhs) const;
    Row& Advance(std::ptrdiff_t);
    //@}
private:
    detail::ResultWrapperPtr res_;
    size_type row_index_{0};
};
 
/// @name Iterator over rows in a result set
class ConstRowIterator : public detail::ConstDataIterator<ConstRowIterator, Row, detail::IteratorDirection::kForward> {
public:
    ConstRowIterator() = default;
 
private:
    friend class ResultSet;
 
    ConstRowIterator(detail::ResultWrapperPtr res, size_type row) : ConstDataIterator(std::move(res), row) {}
};
 
/// @name Reverse iterator over rows in a result set
class ReverseConstRowIterator
    : public detail::ConstDataIterator<ReverseConstRowIterator, Row, detail::IteratorDirection::kReverse> {
public:
    ReverseConstRowIterator() = default;
 
private:
    friend class ResultSet;
 
    ReverseConstRowIterator(detail::ResultWrapperPtr res, size_type row) : ConstDataIterator(std::move(res), row) {}
};
 
/// @brief PostgreSQL result set
///
/// Provides random access to rows via indexing operations
/// and bidirectional iteration via iterators.
///
/// ## Usage synopsis
/// ```
/// auto trx = ...;
/// auto res = trx.Execute("select a, b from table");
/// for (auto row : res) {
///   // Process row data
/// }
/// ```
class ResultSet {
public:
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
    static constexpr size_type npos = std::numeric_limits<size_type>::max();
 
    //@{
    /** @name Row container concept */
    using const_iterator = ConstRowIterator;
    using const_reverse_iterator = ReverseConstRowIterator;
 
    using value_type = Row;
    using reference = value_type;
    using pointer = const_iterator;
    //@}
 
    explicit ResultSet(std::shared_ptr<detail::ResultWrapper> pimpl) : pimpl_{std::move(pimpl)} {}
 
    /// Number of rows in the result set
    size_type Size() const;
    bool IsEmpty() const { return Size() == 0; }
 
    size_type RowsAffected() const;
    std::string CommandStatus() const;
 
    //@{
    /** @name Row container interface */
    //@{
    /** @name Forward iteration */
    const_iterator cbegin() const&;
    const_iterator begin() const& { return cbegin(); }
    const_iterator cend() const&;
    const_iterator end() const& { return cend(); }
 
    // One should store ResultSet before using its accessors
    const_iterator cbegin() const&& = delete;
    const_iterator begin() const&& = delete;
    const_iterator cend() const&& = delete;
    const_iterator end() const&& = delete;
    //@}
    //@{
    /** @name Reverse iteration */
    const_reverse_iterator crbegin() const&;
    const_reverse_iterator rbegin() const& { return crbegin(); }
    const_reverse_iterator crend() const&;
    const_reverse_iterator rend() const& { return crend(); }
    // One should store ResultSet before using its accessors
    const_reverse_iterator crbegin() const&& = delete;
    const_reverse_iterator rbegin() const&& = delete;
    const_reverse_iterator crend() const&& = delete;
    const_reverse_iterator rend() const&& = delete;
    //@}
 
    reference Front() const&;
    reference Back() const&;
    // One should store ResultSet before using its accessors
    reference Front() const&& = delete;
    reference Back() const&& = delete;
 
    /// @brief Access a row by index
    /// @throws RowIndexOutOfBounds if index is out of bounds
    reference operator[](size_type index) const&;
    // One should store ResultSet before using its accessors
    reference operator[](size_type index) const&& = delete;
    //@}
 
    //@{
    /** @name ResultSet metadata access */
    // TODO ResultSet metadata access interface
    size_type FieldCount() const;
    RowDescription GetRowDescription() const& { return {pimpl_}; }
    // One should store ResultSet before using its accessors
    RowDescription GetRowDescription() const&& = delete;
    //@}
 
    //@{
    /** @name Typed results */
    /// @brief Get a wrapper for iterating over a set of typed results.
    /// For more information see @ref psql_typed_results
    template <typename T>
    auto AsSetOf() const;
    template <typename T>
    auto AsSetOf(RowTag) const;
    template <typename T>
    auto AsSetOf(FieldTag) const;
 
    /// @brief Extract data into a container.
    /// For more information see @ref psql_typed_results
    template <typename Container>
    Container AsContainer() const;
    template <typename Container>
    Container AsContainer(RowTag) const;
 
    /// @brief Extract first row into user type.
    /// A single row result set is expected, will throw an exception when result
    /// set size != 1
    template <typename T>
    auto AsSingleRow() const;
    template <typename T>
    auto AsSingleRow(RowTag) const;
    template <typename T>
    auto AsSingleRow(FieldTag) const;
 
    /// @brief Extract first row into user type.
    /// @returns A single row result set if non empty result was returned, empty
    /// std::optional otherwise
    /// @throws exception when result set size > 1
    template <typename T>
    std::optional<T> AsOptionalSingleRow() const;
    template <typename T>
    std::optional<T> AsOptionalSingleRow(RowTag) const;
    template <typename T>
    std::optional<T> AsOptionalSingleRow(FieldTag) const;
    //@}
private:
    friend class detail::ConnectionImpl;
    void FillBufferCategories(const UserTypes& types);
    void SetBufferCategoriesFrom(const ResultSet&);
 
    template <typename T, typename Tag>
    friend class TypedResultSet;
    friend class ConnectionImpl;
 
    std::shared_ptr<detail::ResultWrapper> pimpl_;
};
 
namespace detail {
 
template <typename T>
struct IsOptionalFromOptional : std::false_type {};
 
template <typename T>
struct IsOptionalFromOptional<std::optional<std::optional<T>>> : std::true_type {};
 
template <typename T>
struct IsOneVariant : std::false_type {};
 
template <typename T>
struct IsOneVariant<std::variant<T>> : std::true_type {};
 
template <typename... Args>
constexpr void AssertSaneTypeToDeserialize() {
    static_assert(
        !(IsOptionalFromOptional<std::remove_const_t<std::remove_reference_t<Args>>>::value || ...),
        "Attempt to get an optional<optional<T>> was detected. Such "
        "optional-from-optional types are very error prone, obfuscate code and "
        "are ambiguous to deserialize. Change the type to just optional<T>"
    );
    static_assert(
        !(IsOneVariant<std::remove_const_t<std::remove_reference_t<Args>>>::value || ...),
        "Attempt to get an variant<T> was detected. Such variant from one type "
        "obfuscates code. Change the type to just T"
    );
}
 
//@{
/** @name Sequental field extraction */
template <typename IndexTuple, typename... T>
struct RowDataExtractorBase;
 
template <std::size_t... Indexes, typename... T>
struct RowDataExtractorBase<std::index_sequence<Indexes...>, T...> {
    static void ExtractValues(const Row& row, T&&... val) {
        static_assert(sizeof...(Indexes) == sizeof...(T));
 
        std::size_t field_index = 0;
        const auto perform = [&](auto&& arg) { row.GetFieldView(field_index++).To(std::forward<decltype(arg)>(arg)); };
        (perform(std::forward<T>(val)), ...);
    }
    static void ExtractTuple(const Row& row, std::tuple<T...>& val) {
        static_assert(sizeof...(Indexes) == sizeof...(T));
 
        std::size_t field_index = 0;
        const auto perform = [&](auto& arg) { row.GetFieldView(field_index++).To(arg); };
        (perform(std::get<Indexes>(val)), ...);
    }
    static void ExtractTuple(const Row& row, std::tuple<T...>&& val) {
        static_assert(sizeof...(Indexes) == sizeof...(T));
 
        std::size_t field_index = 0;
        const auto perform = [&](auto& arg) { row.GetFieldView(field_index++).To(arg); };
        (perform(std::get<Indexes>(val)), ...);
    }
 
    static void ExtractValues(const Row& row, const std::initializer_list<std::string>& names, T&&... val) {
        (row[*(names.begin() + Indexes)].To(std::forward<T>(val)), ...);
    }
    static void ExtractTuple(const Row& row, const std::initializer_list<std::string>& names, std::tuple<T...>& val) {
        std::tuple<T...> tmp{row[*(names.begin() + Indexes)].template As<T>()...};
        tmp.swap(val);
    }
 
    static void ExtractValues(const Row& row, const std::initializer_list<std::size_t>& indexes, T&&... val) {
        (row[*(indexes.begin() + Indexes)].To(std::forward<T>(val)), ...);
    }
    static void ExtractTuple(const Row& row, const std::initializer_list<std::size_t>& indexes, std::tuple<T...>& val) {
        std::tuple<T...> tmp{row[*(indexes.begin() + Indexes)].template As<T>()...};
        tmp.swap(val);
    }
};
 
template <typename... T>
struct RowDataExtractor : RowDataExtractorBase<std::index_sequence_for<T...>, T...> {};
 
template <typename T>
struct TupleDataExtractor;
template <typename... T>
struct TupleDataExtractor<std::tuple<T...>> : RowDataExtractorBase<std::index_sequence_for<T...>, T...> {};
//@}
 
template <typename RowType>
constexpr void AssertRowTypeIsMappedToPgOrIsCompositeType() {
    // composite types can be parsed without an explicit mapping
    static_assert(
        io::traits::kIsMappedToPg<RowType> || io::traits::kIsCompositeType<RowType>,
        "Row type must be mapped to pg type(CppToUserPg) or one of the "
        "following: "
        "1. primitive type. "
        "2. std::tuple. "
        "3. Aggregation type. See std::aggregation. "
        "4. Has a Introspect method that makes the std::tuple from your "
        "class/struct. "
        "For more info see `uPg: Typed PostgreSQL results` chapter in docs."
    );
}
 
}  // namespace detail
 
template <typename T>
void Row::To(T&& val) const {
    To(std::forward<T>(val), kFieldTag);
}
 
template <typename T>
void Row::To(T&& val, RowTag) const {
    detail::AssertSaneTypeToDeserialize<T>();
    // Convert the val into a writable tuple and extract the data
    using ValueType = std::decay_t<T>;
    io::traits::AssertIsValidRowType<ValueType>();
    using RowType = io::RowType<ValueType>;
    using TupleType = typename RowType::TupleType;
    constexpr auto tuple_size = RowType::size;
    if (tuple_size > Size()) {
        throw InvalidTupleSizeRequested(Size(), tuple_size);
    } else if (tuple_size < Size()) {
        LOG_LIMITED_WARNING() << "Row size is greater that the number of data members in "
                                 "C++ user datatype "
                              << compiler::GetTypeName<T>();
    }
 
    detail::TupleDataExtractor<TupleType>::ExtractTuple(*this, RowType::GetTuple(std::forward<T>(val)));
}
 
template <typename T>
void Row::To(T&& val, FieldTag) const {
    detail::AssertSaneTypeToDeserialize<T>();
    using ValueType = std::decay_t<T>;
    detail::AssertRowTypeIsMappedToPgOrIsCompositeType<ValueType>();
    // Read the first field into the type
    if (Size() < 1) {
        throw InvalidTupleSizeRequested{Size(), 1};
    }
    if (Size() > 1) {
        throw NonSingleColumnResultSet{Size(), compiler::GetTypeName<T>(), "As"};
    }
    (*this)[0].To(std::forward<T>(val));
}
 
template <typename... T>
void Row::To(T&&... val) const {
    detail::AssertSaneTypeToDeserialize<T...>();
    if (sizeof...(T) > Size()) {
        throw InvalidTupleSizeRequested(Size(), sizeof...(T));
    }
    detail::RowDataExtractor<T...>::ExtractValues(*this, std::forward<T>(val)...);
}
 
template <typename T, typename... Y>
auto Row::As() const {
    if constexpr (sizeof...(Y) > 0) {
        std::tuple<T, Y...> res;
        To(res, kRowTag);
        return res;
    } else {
        return As<T>(kFieldTag);
    }
}
 
template <typename... T>
void Row::To(const std::initializer_list<std::string>& names, T&&... val) const {
    detail::AssertSaneTypeToDeserialize<T...>();
    if (sizeof...(T) != names.size()) {
        throw FieldTupleMismatch(names.size(), sizeof...(T));
    }
    detail::RowDataExtractor<T...>::ExtractValues(*this, names, std::forward<T>(val)...);
}
 
template <typename... T>
std::tuple<T...> Row::As(const std::initializer_list<std::string>& names) const {
    if (sizeof...(T) != names.size()) {
        throw FieldTupleMismatch(names.size(), sizeof...(T));
    }
    std::tuple<T...> res;
    detail::RowDataExtractor<T...>::ExtractTuple(*this, names, res);
    return res;
}
 
template <typename... T>
void Row::To(const std::initializer_list<size_type>& indexes, T&&... val) const {
    detail::AssertSaneTypeToDeserialize<T...>();
    if (sizeof...(T) != indexes.size()) {
        throw FieldTupleMismatch(indexes.size(), sizeof...(T));
    }
    detail::RowDataExtractor<T...>::ExtractValues(*this, indexes, std::forward<T>(val)...);
}
 
template <typename... T>
std::tuple<T...> Row::As(const std::initializer_list<size_type>& indexes) const {
    if (sizeof...(T) != indexes.size()) {
        throw FieldTupleMismatch(indexes.size(), sizeof...(T));
    }
    std::tuple<T...> res;
    detail::RowDataExtractor<T...>::ExtractTuple(*this, indexes, res);
    return res;
}
 
template <typename T>
auto ResultSet::AsSetOf() const {
    return AsSetOf<T>(kFieldTag);
}
 
template <typename T>
auto ResultSet::AsSetOf(RowTag) const {
    detail::AssertSaneTypeToDeserialize<T>();
    using ValueType = std::decay_t<T>;
    io::traits::AssertIsValidRowType<ValueType>();
    return TypedResultSet<T, RowTag>{*this};
}
 
template <typename T>
auto ResultSet::AsSetOf(FieldTag) const {
    detail::AssertSaneTypeToDeserialize<T>();
    using ValueType = std::decay_t<T>;
    detail::AssertRowTypeIsMappedToPgOrIsCompositeType<ValueType>();
    if (FieldCount() > 1) {
        throw NonSingleColumnResultSet{FieldCount(), compiler::GetTypeName<T>(), "AsSetOf"};
    }
    return TypedResultSet<T, FieldTag>{*this};
}
 
template <typename Container>
Container ResultSet::AsContainer() const {
    detail::AssertSaneTypeToDeserialize<Container>();
    using ValueType = typename Container::value_type;
    Container c;
    if constexpr (io::traits::kCanReserve<Container>) {
        c.reserve(Size());
    }
    auto res = AsSetOf<ValueType>();
 
    auto inserter = io::traits::Inserter(c);
    auto row_it = res.begin();
    for (std::size_t i = 0; i < res.Size(); ++i, ++row_it, ++inserter) {
        *inserter = *row_it;
    }
 
    return c;
}
 
template <typename Container>
Container ResultSet::AsContainer(RowTag) const {
    detail::AssertSaneTypeToDeserialize<Container>();
    using ValueType = typename Container::value_type;
    Container c;
    if constexpr (io::traits::kCanReserve<Container>) {
        c.reserve(Size());
    }
    auto res = AsSetOf<ValueType>(kRowTag);
 
    auto inserter = io::traits::Inserter(c);
    auto row_it = res.begin();
    for (std::size_t i = 0; i < res.Size(); ++i, ++row_it, ++inserter) {
        *inserter = *row_it;
    }
 
    return c;
}
 
template <typename T>
auto ResultSet::AsSingleRow() const {
    return AsSingleRow<T>(kFieldTag);
}
 
template <typename T>
auto ResultSet::AsSingleRow(RowTag) const {
    detail::AssertSaneTypeToDeserialize<T>();
    if (Size() != 1) {
        throw NonSingleRowResultSet{Size()};
    }
    return Front().As<T>(kRowTag);
}
 
template <typename T>
auto ResultSet::AsSingleRow(FieldTag) const {
    detail::AssertSaneTypeToDeserialize<T>();
    if (Size() != 1) {
        throw NonSingleRowResultSet{Size()};
    }
    return Front().As<T>(kFieldTag);
}
 
template <typename T>
std::optional<T> ResultSet::AsOptionalSingleRow() const {
    return AsOptionalSingleRow<T>(kFieldTag);
}
 
template <typename T>
std::optional<T> ResultSet::AsOptionalSingleRow(RowTag) const {
    return IsEmpty() ? std::nullopt : std::optional<T>{AsSingleRow<T>(kRowTag)};
}
 
template <typename T>
std::optional<T> ResultSet::AsOptionalSingleRow(FieldTag) const {
    return IsEmpty() ? std::nullopt : std::optional<T>{AsSingleRow<T>(kFieldTag)};
}
 
}  // namespace storages::postgres
 
USERVER_NAMESPACE_END
 
#include <userver/storages/postgres/typed_result_set.hpp>