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From Michael Martineau <m...@familypursuit.com>
Subject Using the Cayenne API to dynamically create DataDomains
Date Thu, 11 Feb 2010 23:29:16 GMT
Hello,

I'm evaluating to see if Cayenne would be a good replacement for 
Hibernate in my current project.  I'm creating a website using tomcat 
where users register on the main website (e.g. www.mydomain.com).  When 
they register, they select their own sub-domain name for a private 
database (e.g. myprivatedb.mydomain.com).  The web app then creates a 
new database instance for them using a common schema.  Thus, each 
database has the exact same structure.  When each user goes to their own 
sub-domain and signs in, they are connecting to their private database 
(I use the sub-domain as a key to determine which database to use).  
However, even though each user is accessing their own database, all 
users are sharing the same JVM tomcat instance.  Furthermore, all 
databases are hosted by the same Mysql server instance.

After combing through the this email list I've been able to piece 
together a simple example of using the Modeler to create a base 
DataDomain/DataMap.  Then using the Cayenne API, I've managed to 
demonstrate to myself the ability to dynamically add new DataDomains 
that use the DataMap template created using the Modeler (see code 
below).  However, in my example, not only am I creating new DataDomains, 
I'm also creating a new connection pool for each DataDomain which is not 
really what I want.  I would like to use the commons-dbcp pool and have 
all users share the same pool of connections to the database server, 
even though they access different schemas (mysql databases).

I've managed to make this work in Hibernate by implementing their 
ConnectionProvider interface.  Each new database configuration 
(SessionFactory) in Hibernate creates a ConnectionProvider which allowed 
me to change the "default" schema on the connection (that I get from the 
DBCP pool) just before handing it to Hibernate based on the website 
sub-domain.  The problem is that Hibernate must create a new 
SessionFactory for every database schema.  Unfortunately, this 
"SessionFactory" takes up a fixed amount of memory (5MB in my case) on 
the server for each new database regardless of whether the user who 
created the private database is signed in and using the website or not.  
What I need is something (Cayenne?) that will take advantage of the fact 
that every database is structurally identical and share the "DataMap" 
resources.

So, here are my questions:
1. How do I use the Cayenne API to dynamically tie into the DBCP 
connection pool?
2. Once I've done that, how do I dynamically switch schemas on a per 
HttpRequest basis?
3. Will the solution work with multiple concurrent users each accessing 
their own database?

In this message: 
http://article.gmane.org/gmane.comp.java.cayenne.user/10428/match=datasource
Andrus suggests a solution that I'm not sure will work in my case where 
every http request will require a schema change.  Has a solution been 
added to the API since this post?

4. Is Cayenne able to solve the memory consumption problem I'm having 
with Hibernate?  I.E., will Cayenne add little to no additional 
dedicated memory resources for every new DataDomain I create if I'm 
using a common database structure for each new database?

Thank you for any help you can give me.

Michael Martineau


Below is the test code I pieced together from several email posts:

public class Main2
{
     public static void main(String[] args) throws SQLException
     {
         Main2 main = new Main2();

         main.createNewDataDomain("db0");
         main.addUser("db0", "Michael");

         main.createNewDataDomain("db1");
         main.addUser("db1", "Rebekah");

         main.createNewDataDomain("db2");
         main.addUser("db2", "Andrew");

         main.createNewDataDomain("db3");
         main.addUser("db3", "Rachael");
     }

     private void createNewDataDomain(String name) throws SQLException
     {
         DataDomain templateDomain = 
Configuration.getSharedConfiguration().getDomain("Cayenne_DBX");

         DataSource dataSource = new 
PoolManager("com.mysql.jdbc.Driver", "jdbc:mysql://localhost/cayenne_" + 
name, 1, 5, "cayenne", "cayenne");

         DataNode dataNode = new DataNode("DynamicNode" + name);
         dataNode.setAdapter(new AutoAdapter(dataSource));
         dataNode.setDataSource(dataSource);
         
dataNode.addDataMap(templateDomain.getEntityResolver().getDataMap("Cayenne_DBXMap"));

         DataDomain domainX = new DataDomain(name);
         domainX.setEntityResolver(templateDomain.getEntityResolver());
         domainX.addNode(dataNode);

         Configuration c = Configuration.getSharedConfiguration();
         c.addDomain(domainX);

     }

     private void addUser(String domain, String username)
     {
         ObjectContext context = DataContext.createDataContext(domain);

         User user = context.newObject(User.class);
         user.setName(username);
         context.commitChanges();

         SelectQuery select1 = new SelectQuery(User.class);
         List<User> users = (List<User>)context.performQuery(select1);

         for(User u : users)
         {
             System.out.println(u.getName());
         }
     }
}




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