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authorwei <>2007-08-30 02:17:55 +0000
committerwei <>2007-08-30 02:17:55 +0000
commit913a2a6e7f036126d123a6b51c5826726246e912 (patch)
tree7b6df6a4d368c3aa245fa799011399c3ede3e8e2 /demos/quickstart
parentc2ca39d96c2320b7dd0433b303d1e778df1edc29 (diff)
add design implications
Diffstat (limited to 'demos/quickstart')
-rw-r--r--demos/quickstart/protected/pages/Database/ActiveRecord.page24
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diff --git a/demos/quickstart/protected/pages/Database/ActiveRecord.page b/demos/quickstart/protected/pages/Database/ActiveRecord.page
index e5ddcdfd..481985e9 100644
--- a/demos/quickstart/protected/pages/Database/ActiveRecord.page
+++ b/demos/quickstart/protected/pages/Database/ActiveRecord.page
@@ -50,6 +50,26 @@
<li>Fetch relationships (related foreign objects) such as "has many", "has one", "belongs to" and "has many" via association table.</li>
<li>Lazy loading of relationships.</li>
</ul>
+<h2>Design Implications</h2>
+<p>
+Prado's implementation of Active Record does not maintain referential identity. Each object obtained using
+Active Record is a copy of the data in the database. For example, If you ask for
+a particular customer and get back a <tt>Customer</tt> object, the next time you ask for
+that customer you get back another instance of a <tt>Customer</tt> object. This implies that a strict
+comparison (i.e., using <tt>===</tt>) will return false, while loose comparison (i.e., using <tt>==</tt>) will
+return true if the object values are equal by loose comparison.
+<p>
+<p>
+This is design implication related to the following question.
+<i>"Do you think of the customer as an object, of which there's only one,
+or do you think of the objects you operate on as <b>copies</b> of the database?"</i>
+Other O/R mappings will imply that there is only one Customer object with custID 100, and it literally is that customer.
+If you get the customer and change a field on it, then you have now changed that customer.
+<i>"That constrasts with: you have changed this copy of the customer, but not that copy.
+And if two people update the customer on two copies of the object, whoever updates first,
+or maybe last, wins."</i> [A. Hejlsberg 2003]
+</p>
+
<h2 id="142010">Database Supported</h2>
<p id="p1" class="block-content">
The Active Record implementation utilizes the <a href="?page=Database.DAO">Prado DAO</a> classes for data access.
@@ -1043,6 +1063,10 @@ will be thrown.
<ul id="u3" class="block-content">
<li>Fowler et. al. <i>Patterns of Enterprise Application Architecture</i>,
Addison Wesley, 2002.</li>
+ <li>B. Venners with B. Eckel. <i><a href="http://www.artima.com/intv/abstract3.html">Inappropriate Abstractions - A Conversation with Anders Hejlsberg, Part VI.</a></i>
+ Artima Developer, 2003.
+ </li>
+
</ul>
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