Any ways to use "space:delete" by part of partial key in Tarantool? - tarantool

Question

The documentation says "delete cannot work with partial keys". What is your recommendation how to solve it. For example create new index, use cycle delete or any way?

Answer 1

You can delete values in a loop using a primary key.
#!/usr/bin/env tarantool
local json = require('json')
local function key_from_tuple(tuple, key_parts)
local key = {}
for _, part in ipairs(key_parts) do
table.insert(key, tuple[part.fieldno] or box.NULL)
end
return key
end
box.cfg{}
box.once('init', function()
box.schema.space.create('s')
box.space.s:create_index('pk')
box.space.s:create_index('sk', {
unique = false,
parts = {
{2, 'number'},
{3, 'number'},
}
})
end)
box.space.s:truncate()
box.space.s:insert{1, 1, 1}
box.space.s:insert{2, 1, 1}
print('before delete')
print('---')
box.space.s:pairs():each(function(tuple)
print(json.encode(tuple))
end)
print('...')
local key_parts = box.space.s.index.pk.parts
for _, tuple in box.space.s.index.sk:pairs({1}) do
local key = key_from_tuple(tuple, key_parts)
box.space.s.index.pk:delete(key)
end
print('after delete')
print('---')
box.space.s:pairs():each(function(tuple)
print(json.encode(tuple))
end)
print('...')
os.exit()
In the example above a common case is handled using key_from_tuple function. Things may be simpler when you know which fields form a primary key. Say, if it is the first field:
for _, tuple in box.space.s.index.sk:pairs({1}) do
box.space.s.index.pk:delete(tuple[1])
end
The new key_def module that was added in tarantool-2.2.0-255-g22db9c264 (not released yet, but availiable from our 2.2 repository) simplifies extracting a key from a tuple, especially in case of json path indexes:
#!/usr/bin/env tarantool
local json = require('json')
local key_def_lib = require('key_def')
box.cfg{}
box.once('init', function()
box.schema.space.create('s')
box.space.s:create_index('pk')
box.space.s:create_index('sk', {
unique = false,
parts = {
{2, 'number', path = 'a'},
{2, 'number', path = 'b'},
}
})
end)
box.space.s:truncate()
box.space.s:insert{1, {a = 1, b = 1}}
box.space.s:insert{2, {a = 1, b = 2}}
print('before delete')
print('---')
box.space.s:pairs():each(function(tuple)
print(json.encode(tuple))
end)
print('...')
local key_def = key_def_lib.new(box.space.s.index.pk.parts)
for _, tuple in box.space.s.index.sk:pairs({1}) do
local key = key_def:extract_key(tuple)
box.space.s.index.pk:delete(key)
end
print('after delete')
print('---')
box.space.s:pairs():each(function(tuple)
print(json.encode(tuple))
end)
print('...')
os.exit()
(source of the code)

Answer 2

Starting from Tarantool 2.1, you can use SQL syntax for that ('delete from ... where ...').
However, be aware that Tarantool will try to perfrom this in a transaction, so if you're trying to delete too many tuples, it will lock transaction thread for some time.