/usr/share/doc/cl-sql/html/csql-rel.html is in cl-sql 6.5.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 | <?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Class Relations</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /><link rel="home" href="index.html" title="CLSQL Users' Guide" /><link rel="up" href="csql.html" title="Chapter 2. CommonSQL Tutorial" /><link rel="prev" href="ch02s02.html" title="Data Modeling with CLSQL" /><link rel="next" href="csql-creat.html" title="Object Creation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Class Relations</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s02.html">Prev</a> </td><th width="60%" align="center">Chapter 2. <span class="application">CommonSQL</span> Tutorial</th><td width="20%" align="right"> <a accesskey="n" href="csql-creat.html">Next</a></td></tr></table><hr /></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="csql-rel"></a>Class Relations</h2></div></div></div><p>
In an <span class="application">SQL</span> only application, the <span class="symbol">EMPLOYEE</span> and
<span class="symbol">COMPANY</span> tables can be queried to determine things
like, "Who is Vladimir's manager?", "What company does Josef work
for?", and "What employees work for Widgets Inc.". This is done by
joining tables with an <span class="application">SQL</span> query.
</p><p>
Who works for Widgets Inc.?
</p><pre class="programlisting">
SELECT first_name, last_name FROM employee, company
WHERE employee.companyid = company.companyid
AND company.company_name = "Widgets Inc."
</pre><p>
Who is Vladimir's manager?
</p><pre class="programlisting">
SELECT managerid FROM employee
WHERE employee.first_name = "Vladimir"
AND employee.last_name = "Lenin"
</pre><p>
What company does Josef work for?
</p><pre class="programlisting">
SELECT company_name FROM company, employee
WHERE employee.first_name = "Josef"
AND employee.last-name = "Stalin"
AND employee.companyid = company.companyid
</pre><p>
With <span class="application"><span class="emphasis"><em>CLSQL</em></span></span> however we do not need to write out such queries because
our view classes can maintain the relations between employees and
companies, and employees to their managers for us. We can then access
these relations like we would any other attribute of an employee or
company object. In order to do this we define some join slots for our
view classes.
</p><p>
What company does an employee work for? If we add the following slot
definition to the employee class we can then ask for it's
<span class="symbol">COMPANY</span> slot and get the appropriate result.
</p><pre class="programlisting">
;; In the employee slot list
(company
:accessor employee-company
:db-kind :join
:db-info (:join-class company
:home-key companyid
:foreign-key companyid
:set nil))
</pre><p>
Who are the employees of a given company? And who is the president of
it? We add the following slot definition to the company view class and
we can then ask for it's <span class="symbol">EMPLOYEES</span> slot and get the
right result.
</p><pre class="programlisting">
;; In the company slot list
(employees
:reader company-employees
:db-kind :join
:db-info (:join-class employee
:home-key companyid
:foreign-key companyid
:set t))
(president
:reader president
:db-kind :join
:db-info (:join-class employee
:home-key presidentid
:foreign-key emplid
:set nil))
</pre><p>
And lastly, to define the relation between an employee and their
manager:
</p><pre class="programlisting">
;; In the employee slot list
(manager
:accessor employee-manager
:db-kind :join
:db-info (:join-class employee
:home-key managerid
:foreign-key emplid
:set nil))
</pre><p>
<span class="application"><span class="emphasis"><em>CLSQL</em></span></span> join slots can represent one-to-one, one-to-many, and
many-to-many relations. Above we only have one-to-one and one-to-many
relations, later we will explain how to model many-to-many relations.
First, let's go over the slot definitions and the available options.
</p><p>
In order for a slot to be a join, we must specify that it's
<span class="symbol">:db-kind</span> <span class="symbol">:join</span>, as opposed to
<span class="symbol">:base</span> or <span class="symbol">:key</span>. Once we do that, we
still need to tell <span class="application"><span class="emphasis"><em>CLSQL</em></span></span> how to create the join statements for the
relation. This is what the <span class="symbol">:db-info</span> option does. It
is a list of keywords and values. The available keywords are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
<span class="symbol">:join-class</span> - The view class to which we want
to join. It can be another view class, or the same view class
as our object.</p></li><li class="listitem"><p>
<span class="symbol">:home-key</span> - The slot(s) in the immediate object
whose value will be compared to the foreign-key slot(s) in the
join-class in order to join the two tables. It can be a single
slot-name, or it can be a list of slot names.</p></li><li class="listitem"><p>
<span class="symbol">:foreign-key</span> - The slot(s) in the join-class
which will be compared to the value(s) of the home-key.
</p></li><li class="listitem"><p>
<span class="symbol">:set</span> - A boolean which if false, indicates that
this is a one-to-one relation, only one object will be returned.
If true, than this is a one-to-many relation, a list of objects
will be returned when we ask for this slots value.
</p></li></ul></div><p>
There are other :join-info options available in <span class="application"><span class="emphasis"><em>CLSQL</em></span></span>, but we will
save those till we get to the many-to-many relation examples.
</p><div class="simplesect"><div class="titlepage"><div><div><h3 class="title"><a id="idp58124320"></a>Object Oriented Class Relations</h3></div></div></div><p>
<span class="application"><span class="emphasis"><em>CLSQL</em></span></span> provides an Object Oriented Data Definition Language, which
provides a mapping from <span class="application">SQL</span> tables to CLOS objects. By default class
inheritance is handled by including all the columns from parent
classes into the child class. This means your database schema becomes
very much denormalized. The class option <span class="symbol">:normalizedp</span>
can be used to disable the default behaviour and have <span class="application"><span class="emphasis"><em>CLSQL</em></span></span>
normalize the database schemas of inherited classes.
</p><p>
See <a class="link" href="def-view-class.html" title="DEF-VIEW-CLASS"><code class="function">def-view-class</code></a>
for more information.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s02.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="csql.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="csql-creat.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Data Modeling with <span class="application"><span class="emphasis"><em>CLSQL</em></span></span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Object Creation</td></tr></table></div></body></html>
|