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
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<LINK type="text/css" rel="stylesheet" href="resources/space.css">
<STYLE type="text/css">
.footer {
background-image: url('http://cwiki.apache.org/confluence/images/border/border_bottom.gif');
background-repeat: repeat-x;
background-position: left top;
padding-top: 4px;
color: #666;
}
</STYLE>
<SCRIPT type="text/javascript" language="javascript">
var hide = null;
var show = null;
var children = null;
function init() {
/* Search form initialization */
var form = document.forms['search'];
if (form != null) {
form.elements['domains'].value = location.hostname;
form.elements['sitesearch'].value = location.hostname;
}
/* Children initialization */
hide = document.getElementById('hide');
show = document.getElementById('show');
children = document.all != null ?
document.all['children'] :
document.getElementById('children');
if (children != null) {
children.style.display = 'none';
show.style.display = 'inline';
hide.style.display = 'none';
}
}
function showChildren() {
children.style.display = 'block';
show.style.display = 'none';
hide.style.display = 'inline';
}
function hideChildren() {
children.style.display = 'none';
show.style.display = 'inline';
hide.style.display = 'none';
}
</SCRIPT>
<TITLE>Concept - ConventionOverConfiguration</TITLE>
<META http-equiv="Content-Type" content="text/html;charset=UTF-8"></HEAD>
<BODY onload="init()">
<TABLE border="0" cellpadding="2" cellspacing="0" width="100%">
<TR class="topBar">
<TD align="left" valign="middle" class="topBarDiv" nowrap="">
<A href="home.html" title="Apache Tuscany">Apache Tuscany</A> > <A href="home.html" title="Home">Home</A> > <A href="das-overview.html" title="DAS Overview">DAS Overview</A> > <A href="das-java-project.html" title="DAS Java Project">DAS Java Project</A> > <A href="rdb-das.html" title="RDB DAS">RDB DAS</A> > <A href="rdb-das-user-guide.html" title="RDB DAS - User Guide">RDB DAS - User Guide</A> > <A href="" title="Concept - ConventionOverConfiguration">Concept - ConventionOverConfiguration</A>
</TD>
<TD align="right" valign="middle" nowrap="">
<FORM name="search" action="http://www.google.com/search" method="get">
<INPUT type="hidden" name="ie" value="UTF-8">
<INPUT type="hidden" name="oe" value="UTF-8">
<INPUT type="hidden" name="domains" value="">
<INPUT type="hidden" name="sitesearch" value="">
<INPUT type="text" name="q" maxlength="255" value="">
<INPUT type="submit" name="btnG" value="Google Search">
</FORM>
</TD>
</TR>
</TABLE>
<DIV id="PageContent">
<DIV class="pageheader" style="padding: 6px 0px 0px 0px;">
<!-- We'll enable this once we figure out how to access (and save) the logo resource -->
<!--img src="/wiki/images/confluence_logo.gif" style="float: left; margin: 4px 4px 4px 10px;" border="0"-->
<DIV style="margin: 0px 10px 0px 10px" class="smalltext">Apache Tuscany</DIV>
<DIV style="margin: 0px 10px 8px 10px" class="pagetitle">Concept - ConventionOverConfiguration</DIV>
<DIV class="greynavbar" align="right" style="padding: 2px 10px; margin: 0px;">
<A href="http://cwiki.apache.org/confluence/pages/editpage.action?pageId=52811">
<IMG src="http://cwiki.apache.org/confluence/images/icons/notep_16.gif" height="16" width="16" border="0" align="absmiddle" title="Edit Page"></A>
<A href="http://cwiki.apache.org/confluence/pages/editpage.action?pageId=52811">Edit Page</A>
<A href="http://cwiki.apache.org/confluence/pages/listpages.action?key=TUSCANY">
<IMG src="http://cwiki.apache.org/confluence/images/icons/browse_space.gif" height="16" width="16" border="0" align="absmiddle" title="Browse Space"></A>
<A href="http://cwiki.apache.org/confluence/pages/listpages.action?key=TUSCANY">Browse Space</A>
<A href="http://cwiki.apache.org/confluence/pages/createpage.action?spaceKey=TUSCANY&fromPageId=52811">
<IMG src="http://cwiki.apache.org/confluence/images/icons/add_page_16.gif" height="16" width="16" border="0" align="absmiddle" title="Add Page"></A>
<A href="http://cwiki.apache.org/confluence/pages/createpage.action?spaceKey=TUSCANY&fromPageId=52811">Add Page</A>
<A href="http://cwiki.apache.org/confluence/pages/createblogpost.action?spaceKey=TUSCANY&fromPageId=52811">
<IMG src="http://cwiki.apache.org/confluence/images/icons/add_blogentry_16.gif" height="16" width="16" border="0" align="absmiddle" title="Add News"></A>
<A href="http://cwiki.apache.org/confluence/pages/createblogpost.action?spaceKey=TUSCANY&fromPageId=52811">Add News</A>
</DIV>
</DIV>
<DIV class="pagesubheading" style="margin: 0px 10px 0px 10px;">
Added by <A href="http://cwiki.apache.org/confluence/users/viewuserprofile.action?username=adriano_crestani">Adriano Crestani</A>, last edited by <A href="http://cwiki.apache.org/confluence/users/viewuserprofile.action?username=lresende@apache.org">Luciano Resende</A> on Apr 29, 2007
(<A href="http://cwiki.apache.org/confluence/pages/diffpages.action?pageId=52811&originalId=52885">view change</A>)
</DIV>
<DIV class="pagecontent">
<DIV class="wiki-content">
<H1><A name="Concept-ConventionOverConfiguration-ConventionOverConfiguration"></A>ConventionOverConfiguration</H1>
<P>This concept reflects the notion that configuration (defining a bunch of stuff in a side file) can be avoided by following convention (adhering to prescribed patterns) and that this is generally a good thing. The RDB DAS has several reasonable conventions in place and using these can significantly reduce a developer's work-load.</P>
<P>As an example, the RDB DAS provides a straight-forward, one-to-one mapping of database tables to DataObject Types and from table columns to DataObject properties. If a user provides no mapping information to the contrary, a graph of DataObjects returned by the DAS will directly map Types/Properties to the Tables/Columns queried.</P>
<P>For example, consider a database with the following table:</P>
<DIV class="code"><DIV class="codeContent">
<PRE class="code-java">TABLE CUSTOMER
ID INTEGER
LASTNAME VARCHAR(20)
ADDRESS VARCHAR(30)</PRE>
</DIV></DIV>
<P>If an application uses the DAS to query this table with the following SQL statement:</P>
<DIV class="preformatted"><DIV class="preformattedContent">
<PRE>SELECT * FROM CUSTOMER
</PRE>
</DIV></DIV>
<P>The DAS will return a graph of DataObjects each of Type CUSTOMER and each instance in will have three properties: (ID, LASTNAME, ADDRESS). Here is the example code. Note that no configuration data is provided at all.</P>
<DIV class="panel"><DIV class="panelContent">
<P>DAS das = DAS.FACTORY.createDAS(getConnection());<BR>
Command readCustomers = das.createCommand("select * from CUSTOMER");<BR>
DataObject root = readCustomers.executeQuery();</P>
</DIV></DIV>
<P>Another piece of convention followed by the RDB DAS has to do with database table keys. When asked to "apply changes", the RDB DAS scans the SDO ChangeSummery and generates the set of INSERT/UPDATE and DELETE statements needed to flush the graph changes to the database. To generate the correct statements the RDB DAS needs to know how a DataObject's properties map to a database table key. In typical Object/Relational mappings frameworks, this information is provided in a config file with something like this:</P>
<DIV class="preformatted"><DIV class="preformattedContent">
<PRE><Table tableName="COMPANY">
<Column columnName="ID" primaryKey="true"/>
.
.
.
</Table>
</PRE>
</DIV></DIV>
<P>However, the RDB DAS understands is that, in the absence of user provided cofiguration data, a DataObject property named "ID" maps to a key column named "ID" in the database. If a developer follows this convention (naming key columns "ID") then this key-mapping information need not be specified in a configuration file.</P>
<P>The RDB DAS also has convention in place for mapping DataObject relationships. If a database table (yyy) has a column named xxx_ID then the DAS will assume, in the absence of config data to the contrary, that there is a one-to-many relationship from table xxx to table yyy and that the key column for table xxx is named "ID".</P>
<P>There is more "convention over configuration" coming. We are currently looking into support for optimistic concurrency control conventions and other areas. </P>
</DIV>
</DIV>
</DIV>
<DIV class="footer">
Generated by
<A href="http://www.atlassian.com/confluence/">Atlassian Confluence</A> (Version: 2.2.9 Build: 527 Sep 07, 2006)
<A href="http://could.it/autoexport/">AutoExport Plugin</A> (Version: Unknown - PluginManager Error)
</DIV>
</BODY>
</HTML>
|
