sqt::CustomValueTraits< T > Class Template Reference

Description

template<typename T>
class sqt::CustomValueTraits< T >

The primary template for defining traits for custom value types.

Template Parameters

T	The custom value type for which to define traits.

This primary template is intended to be specialized by users for each custom value type. Specializing this template allows fields or accessors with custom value types to be used in column definitions via the SQT_COLUMN_FIELD or SQT_COLUMN_ACCESSOR macros.

Specializations must satisfy the sqt::BasicValueTraitsType concept. The following example demonstrates how to define a specialization for a custom value type mapped to the BLOB data type:

// The custom value type.
struct BLOB {
    std::vector<std::byte> data;
};
 
// The specialization must be defined within the `sqt` namespace.
namespace sqt {
 
// The specialization for the BLOB type.
template<>
class CustomValueTraits<BLOB> {
public:
    // This type alias must match the custom value type.
    using ValueType = BLOB;
 
    // Specifies the data type to which the custom value type is mapped.
    static constexpr sqt::DataType DataType = sqt::DataType::BLOB;
 
    // Indicates whether the custom value type is nullable.
    static constexpr bool IsNullable = false;
 
    // Binds the custom value to a statement parameter.
    static void BindValue(sqt::Statement& statement, int parameter_index, const BLOB& blob) {
        statement.BindParameter(parameter_index, blob.data);
    }
 
    // Retrieves the custom value from a statement column.
    static BLOB RetrieveValue(const sqt::Statement& statement, int column_index) {
        auto blob = statement.GetColumnBLOB(column_index);
        BLOB result;
        result.data.assign(blob.begin(), blob.end());
        return result;
    }
};
 
}

See also

sqt::BasicValueTraitsType

SQT_COLUMN_ACCESSOR

SQT_COLUMN_FIELD