index_object extensions

You can extend index_object with custom functions as follows:

Create a Lua function.
Add the function name to a predefined global variable, which has the table type.
Call the function on the index_object: index_object:function-name([parameters]).

There are three predefined global variables:

Adding to box_schema.index_mt makes the function available for all indexes.
Adding to box_schema.memtx_index_mt makes the function available for all memtx indexes.
Adding to box_schema.vinyl_index_mt makes the function available for all vinyl indexes.

Alternatively, you can make a user-defined function available for only one index by calling getmetatable(index_object) and then adding the function name to the meta table.

Example 1:

The example below shows how to extend all memtx indexes with the custom function:

box.schema.space.create('tester1', { engine = 'memtx' })
box.space.tester1:create_index('index1')
global_counter = 5

-- Create a custom function.
function increase_global_counter()
    global_counter = global_counter + 1
end

-- Extend all memtx indexes with the created function.
box.schema.memtx_index_mt.increase_global_counter = increase_global_counter

-- Call the 'increase_global_counter' function on 'index1'
-- to change the 'global_counter' value from 5 to 6.
box.space.tester1.index.index1:increase_global_counter()

Example 2:

The example below shows how to extend the specified index with the custom function with parameters:

box.schema.space.create('tester2', { engine = 'memtx', id = 1000 })
box.space.tester2:create_index('index2')
local_counter = 0

-- Create a custom function.
function increase_local_counter(i_arg, param)
    local_counter = local_counter + param + i_arg.space_id
end

-- Extend only the 'index2' index with the created function.
box.schema.memtx_index_mt.increase_local_counter = increase_local_counter
meta = getmetatable(box.space.tester2.index.index2)
meta.increase_local_counter = increase_local_counter

-- Call the 'increase_local_counter' function on 'index2'
-- to change the 'local_counter' value from 0 to 1005.
box.space.tester2.index.index2:increase_local_counter(5)

Version:

index_object extensions