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box.ctl.on_schema_init()
Create a "schema_init :ref:`trigger <triggers>`". The ``trigger-function`` will be executed when :ref:`box.cfg{} <index-book_cfg>` happens for the first time. That is, the ``schema_init`` trigger is called before the server's configuration and recovery begins, and therefore ``box.ctl.on_schema_init`` must be called before ``box.cfg`` is called.
Parameters
function which will become the trigger function
existing trigger function which will be replaced by trigger-function
return
nil or function pointer
If the parameters are (nil, old-trigger-function), then the old trigger is deleted.
A common use is: make a ``schema_init`` trigger function which creates a ``before_replace`` trigger function on a system space. Thus, since system spaces are created when the server starts, the ``before_replace`` triggers will be activated for each tuple in each system space. For example, such a trigger could change the storage engine of a given space, or make a given space :ref:`replica-local <replication-local>` while a replica is being bootstrapped. Making such a change after ``box.cfg`` is not reliable because other connections might use the database before the change is made.
Details about trigger characteristics are in the :ref:`triggers <triggers-box_triggers>` section.
**Example:**
Suppose that, before the server is fully up and ready for connections, you want to make sure that the engine of space ``space_name`` is vinyl. So you want to make a trigger that will be activated when a tuple is inserted in the ``_space`` system space. In this case you could end up with a master that has space-name with ``engine='memtx'`` and a replica that has space_name with ``engine='vinyl'``, with the same contents.
function function_for_before_replace(old, new)
if old == nil and new ~= nil and new[3] == 'space_name' and new[4] ~= 'vinyl' then
return new:update{{'=', 4, 'vinyl'}}
end
end

box.ctl.on_schema_init(function()
box.space._space:before_replace(function_for_before_replace)
end)

box.cfg{replication='master_uri', ...}

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testing_project / Documentation: reference/reference_lua/box_ctl/on_schema_init — English

function function_for_before_replace(old, new)
if old == nil and new ~= nil and new[3] == 'space_name' and new[4] ~= 'vinyl' then
return new:update{{'=', 4, 'vinyl'}}
end
end

box.ctl.on_schema_init(function()
box.space._space:before_replace(function_for_before_replace)
end)

box.cfg{replication='master_uri', ...}
a year ago
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