Re: Using alternate key instead of primary key when relating an class descriptor with a collection descriptor
I don't think what you want is possible because it goes against concepts
of row indentity and referential integrity.
A foreign key in one table implies a relation to the primary key in the
other table, and there can be only one primary key.
The normal way to specify the relationship you want is to add a user id
attribute to the UserRole class and use the inverse-foreignkey attribute
in the user roles' collection descriptor.
Pulat
Sean Dockery wrote:
Hello.
I've searched the gmane archives, but I was unable to find any messages
related to my question.
Suppose that I have the following classes...
public class User {
private Integer id; // primary key field
private String username; // alternate key field
private Collection userRoles; // collection of UserRole objects related
by username
};
public class UserRole {
private String username; // foreign key
private String rolename;
}
...and I wanted to relate User and UserRole in a repository mapping based
on the equality of the username fields in both User and UserRole. Can this
exact schema be handled through a repository mapping? (Does
fk-pointing-to-this-class work without using an indirection-table? Is
there an alternative?)
Most of the rest of the data model in the application uses User.id as a
foreign key, so we can't easily change the primary key of the user table.
The UserRole fields were chosen for compatibility with Tomcat
JDBCRealm-like declarative security implementations.
The only way that I can see to work around this problem is to duplicate the
User.id field in the UserRole table, along with the username.
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Re: Using alternate key instead of primary key when relating an class descriptor with a collection descriptor
Look at:
doc/docu/guides/basic-technique.html#Support+for+Non-Decomposed+m%3An+Mappings
in the OJB documentation. I think I was able to get something along
these lines to work in a test (pre- 1.0). I think it would be
relatively straight forward for you to implement a test and see if it
works; I would simpy mark the username as a key, and then try it.
Changes to the OJB meta-data that prevent this would be my main concern
Sean Dockery wrote:
Hello.
I've searched the gmane archives, but I was unable to find any messages
related to my question.
Suppose that I have the following classes...
public class User {
private Integer id; // primary key field
private String username; // alternate key field
private Collection userRoles; // collection of UserRole objects related
by username
};
public class UserRole {
private String username; // foreign key
private String rolename;
}
...and I wanted to relate User and UserRole in a repository mapping based
on the equality of the username fields in both User and UserRole. Can this
exact schema be handled through a repository mapping? (Does
fk-pointing-to-this-class work without using an indirection-table? Is
there an alternative?)
Most of the rest of the data model in the application uses User.id as a
foreign key, so we can't easily change the primary key of the user table.
The UserRole fields were chosen for compatibility with Tomcat
JDBCRealm-like declarative security implementations.
The only way that I can see to work around this problem is to duplicate the
User.id field in the UserRole table, along with the username.
-
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--
Robert r. Sanders
Chief Technologist
iPOV
www.ipov.net
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Re: Using alternate key instead of primary key when relating an class descriptor with a collection descriptor
I'll have a look at the documentation; thanks for the link.
Robert r. Sanders [EMAIL PROTECTED] wrote in message
news:[EMAIL PROTECTED]
Look at:
doc/docu/guides/basic-technique.html#Support+for+Non-Decomposed+m%3An+Mappings
in the OJB documentation. I think I was able to get something along
these lines to work in a test (pre- 1.0). I think it would be relatively
straight forward for you to implement a test and see if it works; I
would simpy mark the username as a key, and then try it. Changes to the
OJB meta-data that prevent this would be my main concern
Sean Dockery wrote:
Hello.
I've searched the gmane archives, but I was unable to find any messages
related to my question.
Suppose that I have the following classes...
public class User {
private Integer id; // primary key field
private String username; // alternate key field
private Collection userRoles; // collection of UserRole objects
related by username
};
public class UserRole {
private String username; // foreign key
private String rolename;
}
...and I wanted to relate User and UserRole in a repository mapping based
on the equality of the username fields in both User and UserRole. Can
this exact schema be handled through a repository mapping? (Does
fk-pointing-to-this-class work without using an indirection-table? Is
there an alternative?)
Most of the rest of the data model in the application uses User.id as a
foreign key, so we can't easily change the primary key of the user table.
The UserRole fields were chosen for compatibility with Tomcat
JDBCRealm-like declarative security implementations.
The only way that I can see to work around this problem is to duplicate
the User.id field in the UserRole table, along with the username.
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
--
Robert r. Sanders
Chief Technologist
iPOV
www.ipov.net
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
Re: Using alternate key instead of primary key when relating an class descriptor with a collection descriptor
I don't think what you want is possible because it goes against concepts
of row indentity and referential integrity.
Sorry, but that is incorrect.
There is no restriction on having more than one key that can uniquely
identify a row. All of the keys which can serve to identify a row are
called candidate keys. From the candidate keys, one of the keys is chosen
as the primary key; the remaining keys are then referred to as alternate
keys.
A foreign key in one table implies a relation to the primary key in the
other table, and there can be only one primary key.
The normal way to specify the relationship you want is to add a user id
attribute to the UserRole class and use the inverse-foreignkey attribute
in the user roles' collection descriptor.
Over lunch, I had a discussion with a colleague about this. One issue that
came up during the discussion was that if your alternate key can change,
then it should not be used as the foreign key part of a composite primary
key in a related table because primary keys should never change. So, by
virtue that you would have to cascade the alternate key changes to the
primary key of a related table, then the alternate key is no longer
acceptable as a foreign key in the related table.
One other solution that came up was to have the following tables...
User (userId, username, password)
UserRole (userId, rolename)
...and the following view...
UserRoleView (username, rolename)
...based on the User/UserRole relationship. This approach nicely achieves
my goal of preserving normalization (not duplicating both userId and
username in the UserRole table), and still providing the data navigation
required by DataSourceRealm/JDBCRealm to find roles based on
username/password credentials.
So, I get to have my cake (UserRoles collection in the User class based on
userId relationship to UserRole) and eat it too (still compatible with
Tomcat Realms).
Pulat Yunusov [EMAIL PROTECTED] wrote in message
news:[EMAIL PROTECTED]
I don't think what you want is possible because it goes against concepts
of row indentity and referential integrity.
A foreign key in one table implies a relation to the primary key in the
other table, and there can be only one primary key.
The normal way to specify the relationship you want is to add a user id
attribute to the UserRole class and use the inverse-foreignkey attribute
in the user roles' collection descriptor.
Pulat
Sean Dockery wrote:
Hello.
I've searched the gmane archives, but I was unable to find any messages
related to my question.
Suppose that I have the following classes...
public class User {
private Integer id; // primary key field
private String username; // alternate key field
private Collection userRoles; // collection of UserRole objects
related by username
};
public class UserRole {
private String username; // foreign key
private String rolename;
}
...and I wanted to relate User and UserRole in a repository mapping
based on the equality of the username fields in both User and UserRole.
Can this exact schema be handled through a repository mapping? (Does
fk-pointing-to-this-class work without using an indirection-table? Is
there an alternative?)
Most of the rest of the data model in the application uses User.id as a
foreign key, so we can't easily change the primary key of the user
table.
The UserRole fields were chosen for compatibility with Tomcat
JDBCRealm-like declarative security implementations.
The only way that I can see to work around this problem is to duplicate
the User.id field in the UserRole table, along with the username.
-
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For additional commands, e-mail: [EMAIL PROTECTED]
