clickhouse_io

Table of Contents

• Supported Clickhouse types:
• Example usage:

uClickHouse driver doesn't expose underlying ClickHouse types and only provides a way to convert results to strongly-typed structs/containers (see storages::clickhouse::ExecutionResult).

As naive mapping is ambiguous for some types, namely for chrono and string, explicit mapping is required by the driver - explicit specialization of CppToClickhouse template.

Supported Clickhouse types:

• DateTime storages::clickhouse::io::columns::DateTimeColumn
• DateTime64([3, 6, 9]) storages::clickhouse::io::columns::DateTime64Column
• Int8 storages::clickhouse::io::columns::Int8Column
• Int32 storages::clickhouse::io::columns::Int32Column
• Int64 storages::clickhouse::io::columns::Int64Column
• UInt8 storages::clickhouse::io::columns::UInt8Column
• UInt16 storages::clickhouse::io::columns::UInt16Column
• UInt32 storages::clickhouse::io::columns::UInt32Column
• UInt64 storages::clickhouse::io::columns::UInt64Column
• String storages::clickhouse::io::columns::StringColumn
• UUID storages::clickhouse::io::columns::UuidColumn
• Nullable storages::clickhouse::io::columns::NullableColumn
• Float32 storages::clickhouse::io::columns::Float32Column
• Float64 storages::clickhouse::io::columns::Float64Column

Example usage:

namespace {
 
struct Data final {
  std::vector<uint64_t> numbers;
  std::vector<std::string> strings;
  std::vector<uint64_t> other_numbers;
  std::vector<std::chrono::system_clock::time_point> tps;
};
 
struct RowData final {
  uint64_t number;
  std::string string;
  uint64_t other_number;
  std::chrono::system_clock::time_point tp;
};
 
}  // namespace
 
namespace storages::clickhouse::io {
 
template <>
struct CppToClickhouse<Data> final {
  using mapped_type =
      std::tuple<columns::UInt64Column, columns::StringColumn,
                 columns::UInt64Column, columns::DateTime64ColumnNano>;
};
 
template <>
struct CppToClickhouse<RowData> final {
  using mapped_type =
      std::tuple<columns::UInt64Column, columns::StringColumn,
                 columns::UInt64Column, columns::DateTime64ColumnNano>;
};
 
}  // namespace storages::clickhouse::io