index_object extensions

You can extend index_object with custom functions as follows:

1. Create a Lua function.
2. Add the function name to a predefined global variable, which has the table type.
3. 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 + 1end-- 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_idend-- Extend only the 'index2' index with the created function.box.schema.memtx_index_mt.increase_local_counter = increase_local_countermeta = 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)