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Add PostgreSQL FOR UPDATE getters

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Add a PostgreSQL-specific getRecordForUpdate helper that appends FOR
UPDATE to the generated SELECT statement so callers can lock a row
inside an explicit transaction.

generateProcsForModels now always emits a direct-connection
get<RecordName>ForUpdate proc that accepts db_postgres.DbConn. There is
intentionally no dbType overload for this API, because reacquiring a
connection via withConnection would defeat the lock's transactional
scope.

The source docs and README now document the new helper and show the
intended usage pattern inside inTransaction:

  db.inTransaction:
    var item = conn.getTodoItemForUpdate(todoId)
    item.priority += 1
    discard conn.updateTodoItem(item)
This commit is contained in:
Jonathan Bernard
2026-03-24 22:04:39 -05:00
parent 71cb5a7cff
commit 2301da8143
2 changed files with 35 additions and 3 deletions
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5
README.rst
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@@ -109,6 +109,7 @@ This will generate procedures like the following in two flavors:
.. code-block:: Nim
proc getTodoItem*(db: TodoDB, id: UUID): TodoItem;
proc getTodoItem*[D: DbConnType](conn: D, id: UUID): TodoItem;
proc getTodoItemForUpdate*(conn: db_postgres.DbConn, id: UUID): TodoItem;
proc tryGetTodoItem*(db: TodoDB, id: UUID): Option[TodoItem];
proc tryGetTodoItem*[D: DbConnType](conn: D, id: UUID): Option[TodoItem];
proc getTodoItemIfItExists*(db: TodoDB, id: UUID): Option[TodoItem];
@@ -170,6 +171,8 @@ This will generate procedures like the following in two flavors:
Use the `dbType` flavor when the caller does not already have a connection.
Use the connection flavor inside `withConnection` or `inTransaction`.
The generated `get<RecordName>ForUpdate` helper is PostgreSQL-specific and
is only available for direct PostgreSQL connections.
Warning: do not call the `dbType` flavor from inside `inTransaction`.
Those overloads call `withConnection` and may acquire a different
@@ -178,7 +181,7 @@ transaction.
.. code-block:: Nim
db.inTransaction:
var item = conn.getTodoItem(todoId)
var item = conn.getTodoItemForUpdate(todoId)
item.priority += 1
discard conn.updateTodoItem(item)