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84 lines
2.9 KiB
Plaintext
84 lines
2.9 KiB
Plaintext
;; Copyright (c) 2008-2013 Robert Virding
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;;
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;; Licensed under the Apache License, Version 2.0 (the "License");
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;; you may not use this file except in compliance with the License.
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;; You may obtain a copy of the License at
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;;
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;; http://www.apache.org/licenses/LICENSE-2.0
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;;
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;; Unless required by applicable law or agreed to in writing, software
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;; distributed under the License is distributed on an "AS IS" BASIS,
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;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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;; See the License for the specific language governing permissions and
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;; limitations under the License.
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;; File : mnesia_demo.lfe
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;; Author : Robert Virding
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;; Purpose : A simple Mnesia demo file for LFE.
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;; This file contains a simple demo of using LFE to access Mnesia
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;; tables. It shows how to use the emp-XXXX macro (ETS match pattern)
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;; together with mnesia:match_object, match specifications with
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;; mnesia:select and Query List Comprehensions.
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(defmodule mnesia_demo
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(export (new 0) (by_place 1) (by_place_ms 1) (by_place_qlc 1)))
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(defrecord person name place job)
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(defun new ()
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;; Start mnesia and create a table, we will get an in memory only schema.
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(: mnesia start)
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(: mnesia create_table 'person '(#(attributes (name place job))))
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;; Initialise the table.
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(let ((people '(
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;; First some people in London.
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#(fred london waiter)
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#(bert london waiter)
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#(john london painter)
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#(paul london driver)
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;; Now some in Paris.
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#(jean paris waiter)
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#(gerard paris driver)
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#(claude paris painter)
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#(yves paris waiter)
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;; And some in Rome.
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#(roberto rome waiter)
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#(guiseppe rome driver)
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#(paulo rome painter)
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;; And some in Berlin.
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#(fritz berlin painter)
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#(kurt berlin driver)
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#(hans berlin waiter)
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#(franz berlin waiter)
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)))
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(: lists foreach (match-lambda
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([(tuple n p j)]
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(: mnesia transaction
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(lambda ()
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(let ((new (make-person name n place p job j)))
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(: mnesia write new))))))
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people)))
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;; Match records by place using match_object and the emp-XXXX macro.
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(defun by_place (place)
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(: mnesia transaction
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(lambda () (: mnesia match_object (emp-person place place)))))
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;; Use match specifications to match records
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(defun by_place_ms (place)
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(let ((f (lambda () (: mnesia select 'person
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(match-spec ([(match-person name n place p job j)]
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(when (=:= p place))
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(tuple n j)))))))
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(: mnesia transaction f)))
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;; Use Query List Comprehensions to match records
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(defun by_place_qlc (place)
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(let ((f (lambda ()
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(let ((q (qlc (lc ((<- person (: mnesia table 'person))
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(=:= (person-place person) place))
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person))))
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(: qlc e q)))))
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(: mnesia transaction f)))
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