FAQ
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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postedFeb 11, '10 at 11:30p
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