Hi,
Consider the following n-m relationship:
mysql> desc User;
+------------+--------------+-----+
| Field | Type | Key |
+------------+--------------+-----+
| userId | varchar(50) | PRI |
| password | varchar(250) | |
+------------+--------------+-----+
mysql> desc UserRole;
+--------+-------------+-----+
| Field | Type | Key |
+--------+-------------+-----+
| userId | varchar(50) | PRI | <- foreign key to User.userId
| roleId | varchar(50) | PRI | <- foreign key to Role.roleId
+--------+-------------+-----+
mysql> desc Role;
+-------------+--------------+-----+
| Field | Type | Key |
+-------------+--------------+-----+
| roleId | varchar(50) | PRI |
| description | varchar(250) | |
+-------------+--------------+-----+
Due to my GUI (a multiple selection listbox -- or a picklist; I've another
GUI to add/change the Role's data), I want to make a method call that looks
like create(userId, password, roleIds[]), note that I just have the roleId,
and not the whole Role object/row.
In JDBC, I just need to insert a record in User, and another record in
UserRole (with the given roleId, and the new userId), there's no need to
lookup the Role table.
If I use Castor n-m relationship, I need to look up Role objects using
roleIds, and call a method, such as create(userId, password, roles). This's
a unnecessary overhead (more network traffic and round-trip). n-m works
great only if I need to add a new Role, and bind it to a new User.
I can drop the Role table (it's a dummy table anyway), and use 1:n
relationship. But the dependent object, i.e. UserRole, must have an identity
field (unique), and UserRole will contain only roleId as its only property.
So I cannot make this to behave like an association table, unless I have an
extra primary key column in UserRole.
Any suggestion to model this?
Thanks
Thomas
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