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field numbers and types. There must be at least one part. Every part must contain the attributes ``type`` and ``fieldno``/``field``. Other attributes are optional.
returns
:ref:`a key_def object <key_def-object>`
The parts table has components which are the same as the ``parts`` option in :ref:`Options for space_object:create_index() <index_opts_object>`.
``fieldno`` (integer), for example, ``fieldno = 1``. It is legal to use ``field`` instead of ``fieldno``.
``type`` (string), for example, ``type = 'string'``.
Other components are optional.
Example: ``key_def.new({{type = 'unsigned', fieldno = 1}})``
Example: ``key_def.new({{type = 'string', collation = 'unicode', field = 2}})``
A key_def object is an object returned by :ref:`key_def.new() <key_def-new>`. It has methods :ref:`extract_key() <key_def-extract_key>`, :ref:`compare() <key_def-compare>`, :ref:`compare_with_key() <key_def-compare_with_key>`, :ref:`merge() <key_def-merge>`, :ref:`totable() <key_def-totable>`.
Return a tuple containing only the fields of the ``key_def`` object.
tuple or Lua table with field contents
return
the fields defined for the ``key_def`` object
**Example #1:**
-- Suppose an item has five fields
-- 1, 99.5, 'X', nil, 99.5
-- and the fields that we care about are
-- #3 (a string) and #1 (an integer).
-- We can define those fields with k = key_def.new
-- and extract the values with k:extract_key.

tarantool> key_def = require('key_def')
---
...

tarantool> k = key_def.new({{type = 'string', fieldno = 3},
> {type = 'unsigned', fieldno = 1}})
---
...

tarantool> k:extract_key({1, 99.5, 'X', nil, 99.5})
---
- ['X', 1]
...
**Example #2**
-- Now suppose the item is a tuple in a space with
-- an index on field #3 plus field #1.
-- We can use key_def.new with the index definition
-- instead of filling it out (Example #1).
-- The result will be the same.
key_def = require('key_def')
box.schema.space.create('T')
i = box.space.T:create_index('I', {parts={3, 'string', 1, 'unsigned'}})
box.space.T:insert{1, 99.5, 'X', nil, 99.5}
k = key_def.new(i.parts)
k:extract_key(box.space.T:get({'X', 1}))
**Example #3**
-- Iterate through the tuples in a secondary non-unique index
-- extracting the tuples' primary-key values, so they could be deleted
-- using a unique index. This code should be a part of a Lua function.
local key_def_lib = require('key_def')
local s = box.schema.space.create('test')
local pk = s:create_index('pk')
local sk = s:create_index('test', {unique = false, parts = {
{2, 'number', path = 'a'}, {2, 'number', path = 'b'}}})
s:insert{1, {a = 1, b = 1}}
s:insert{2, {a = 1, b = 2}}
local key_def = key_def_lib.new(pk.parts)
for _, tuple in sk:pairs({1})) do
local key = key_def:extract_key(tuple)
pk:delete(key)
end
Compare the key fields of ``tuple_1`` with the key fields of ``tuple_2``. It is a tuple-by-tuple comparison so users do not have to write code that compares one field at a time. Each field's type and collation will be taken into account. In effect it is a comparison of ``extract_key(tuple_1)`` with ``extract_key(tuple_2)``.
> 0 if tuple_1 key fields > tuple_2 key fields, = 0 if tuple_1 key fields = tuple_2 key fields, < 0 if tuple_1 key fields < tuple_2 key fields
**Example:**
-- This will return 0
key_def = require('key_def')
k = key_def.new({{type = 'string', fieldno = 3, collation = 'unicode_ci'},
{type = 'unsigned', fieldno = 1}})
k:compare({1, 99.5, 'X', nil, 99.5}, {1, 99.5, 'x', nil, 99.5})
Compare the key fields of ``tuple_1`` with all the fields of ``tuple_2``. This is the same as :ref:`key_def_object:compare() <key_def-compare>` except that ``tuple_2`` contains only the key fields. In effect it is a comparison of ``extract_key(tuple_1)`` with ``tuple_2``.
> 0 if tuple_1 key fields > tuple_2 fields, = 0 if tuple_1 key fields = tuple_2 fields, < 0 if tuple_1 key fields < tuple_2 fields
-- Returns 0
key_def = require('key_def')
k = key_def.new({{type = 'string', fieldno = 3, collation = 'unicode_ci'},
{type = 'unsigned', fieldno = 1}})
k:compare_with_key({1, 99.5, 'X', nil, 99.5}, {'x', 1})
Combine the main ``key_def_object`` with ``other_key_def_object``. The return value is a new ``key_def_object`` containing all the fields of the main ``key_def_object``, then all the fields of ``other_key_def_object`` which are not in the main ``key_def_object``.
definition of fields to add
key_def_object
-- Returns a key definition with fieldno = 3 and fieldno = 1.
key_def = require('key_def')
k = key_def.new({{type = 'string', fieldno = 3}})
k2= key_def.new({{type = 'unsigned', fieldno = 1},
{type = 'string', fieldno = 3}})
k:merge(k2)

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testing_project / Documentation: reference/reference_lua/key_def — English

-- Suppose an item has five fields
-- 1, 99.5, 'X', nil, 99.5
-- and the fields that we care about are
-- #3 (a string) and #1 (an integer).
-- We can define those fields with k = key_def.new
-- and extract the values with k:extract_key.

tarantool> key_def = require('key_def')
---
...

tarantool> k = key_def.new({{type = 'string', fieldno = 3},
> {type = 'unsigned', fieldno = 1}})
---
...

tarantool> k:extract_key({1, 99.5, 'X', nil, 99.5})
---
- ['X', 1]
...
2 years ago
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