Multi

kura_multi provides transaction pipelines that group multiple repo operations into a single atomic transaction. If any step fails, the entire transaction is rolled back.

Creating a Pipeline

Multi = kura_multi:new().

Adding Steps

Each step has a unique name (atom) and an operation.

Insert

CS = kura_changeset:cast(my_user, #{}, #{~"name" => ~"Alice"}, [name]),
M1 = kura_multi:insert(Multi, create_user, CS).

Update

CS = kura_changeset:cast(my_user, ExistingUser, #{~"name" => ~"Bob"}, [name]),
M1 = kura_multi:update(Multi, update_user, CS).

Delete

CS = kura_changeset:cast(my_user, User, #{}, []),
M1 = kura_multi:delete(Multi, delete_user, CS).

Run (arbitrary function)

M1 = kura_multi:run(Multi, send_email, fun(Results) ->
    User = maps:get(create_user, Results),
    %% do something...
    {ok, sent}
end).

Dynamic Steps with Functions

Steps can take a function that receives previous results, enabling dependent operations:

Multi = kura_multi:new(),
M1 = kura_multi:insert(Multi, create_user,
    kura_changeset:cast(my_user, #{}, #{~"name" => ~"Alice"}, [name])),
M2 = kura_multi:insert(M1, create_profile, fun(#{create_user := User}) ->
    kura_changeset:cast(my_profile, #{}, #{~"user_id" => maps:get(id, User)}, [user_id])
end).

Executing

case kura_repo_worker:multi(my_repo, Multi) of
    {ok, Results} ->
        %% Results is a map of step_name => result
        User = maps:get(create_user, Results),
        Profile = maps:get(create_profile, Results);
    {error, FailedStep, Value, Completed} ->
        %% FailedStep: atom name of the failed step
        %% Value: the error value
        %% Completed: map of successfully completed steps before failure
        io:format("Step ~p failed: ~p~n", [FailedStep, Value])
end.

Appending Multis

Combine two multi pipelines:

Combined = kura_multi:append(Multi1, Multi2).

Operations from Multi2 are appended after Multi1. Step names must be unique across both.

Error Handling

• If a step returns {error, Value}, the transaction is rolled back
• For insert/update/delete steps, errors come from changeset validation or DB constraint violations
• For run steps, your function must return {ok, Result} or {error, Reason}
• Duplicate step names raise an error at build time: {duplicate_step, Name}