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Diffstat (limited to 'demos/quickstart')
| -rw-r--r-- | demos/quickstart/protected/pages/Database/ActiveRecord.page | 24 |
1 files changed, 24 insertions, 0 deletions
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> <div class="last-modified">$Id$</div></com:TContent>
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