morph::journal::PayloadMigrationRegistry Class Reference

Registry of payload migrations, keyed by (actionType, fromSchema). More...

#include <journal.hpp>

Public Types
using	Migration = std::function<std::string(std::string_view)>
	Rewrites one recorded payload JSON into the current shape.

Public Member Functions
void	add (std::string_view actionType, std::string_view fromSchema, Migration migration)
	Registers migration for entries of actionType stamped with fromSchema. Replaces any migration already registered for that exact pair.
const Migration *	find (std::string_view actionType, std::string_view fromSchema) const
	Looks up the migration for (actionType, fromSchema).
void	clear ()
	Removes every registered migration.
std::size_t	size () const noexcept
	Returns how many migrations are registered.

Detailed Description

Registry of payload migrations, keyed by (actionType, fromSchema).

The escape hatch that makes "refuse on mismatch" a livable contract rather than a one-way door. A migration is a pure function over the recorded payload JSON: given the bytes an older build wrote, return the bytes this build's ActionTraits<A>::fromJson should see. Reconstruction applies it in memory only — the journal on disk is never rewritten, so the recorded history stays exactly what was recorded and the migration stays reviewable as code.

Thread safety

None, matching morph::model::detail::ActionDispatcher: register every migration during start-up, before any replay() can run.

morph::journal::PayloadMigrationRegistry migrations;
migrations.add("setState", oldFingerprint, [](std::string_view payload) {
    // rename "state" -> "stateCode"
    return rewriteKey(payload, "state", "stateCode");
});
auto holder = morph::journal::replay("Sample", log.entries(), registry, dispatcher, migrations);

Definition at line 107 of file journal.hpp.

Member Typedef Documentation

Migration

using morph::journal::PayloadMigrationRegistry::Migration = std::function<std::string(std::string_view)>

Rewrites one recorded payload JSON into the current shape.

Definition at line 110 of file journal.hpp.

Member Function Documentation

add()

void morph::journal::PayloadMigrationRegistry::add ( std::string_view actionType, std::string_view fromSchema, Migration migration )

inline

Registers migration for entries of actionType stamped with fromSchema. Replaces any migration already registered for that exact pair.

Parameters

actionType	LogEntry::actionType the migration applies to.
fromSchema	LogEntry::schema value the migration reads.
migration	Payload rewriter.

Definition at line 118 of file journal.hpp.

find()

const Migration * morph::journal::PayloadMigrationRegistry::find ( std::string_view actionType, std::string_view fromSchema ) const

inlinenodiscard

Looks up the migration for (actionType, fromSchema).

Returns a pointer into the registry, valid until the entry is replaced or the registry is destroyed (std::unordered_map does not invalidate references to surviving elements on rehash).

Parameters

actionType	LogEntry::actionType to match.
fromSchema	LogEntry::schema to match.

Returns

Pointer to the migration, or nullptr if none is registered — into this registry, so valid only for as long as it is.

Definition at line 131 of file journal.hpp.

clear()

void morph::journal::PayloadMigrationRegistry::clear ( )

inline

Removes every registered migration.

Definition at line 138 of file journal.hpp.

size()

std::size_t morph::journal::PayloadMigrationRegistry::size ( ) const

inlinenodiscardnoexcept

Returns how many migrations are registered.

Returns

The registration count.

Definition at line 142 of file journal.hpp.

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The documentation for this class was generated from the following file:

• morph/journal/journal.hpp