How to map combinations of things to a relational database?
Posted
by Space_C0wb0y
on Stack Overflow
See other posts from Stack Overflow
or by Space_C0wb0y
Published on 2010-05-19T11:03:53Z
Indexed on
2010/05/19
11:10 UTC
Read the original article
Hit count: 227
I have a table whose records represent certain objects. For the sake of simplicity I am going to assume that the table only has one row, and that is the unique ObjectId
. Now I need a way to store combinations of objects from that table. The combinations have to be unique, but can be of arbitrary length. For example, if I have the ObjectId
s
1,2,3,4
I want to store the following combinations:
{1,2}, {1,3,4}, {2,4}, {1,2,3,4}
The ordering is not necessary. My current implementation is to have a table Combinations
that maps ObjectId
s to CombinationId
s. So every combination receives a unique Id:
ObjectId | CombinationId
------------------------
1 | 1
2 | 1
1 | 2
3 | 2
4 | 2
This is the mapping for the first two combinations of the example above. The problem is, that the query for finding the CombinationId
of a specific Combination seems to be very complex. The two main usage scenarios for this table will be to iterate over all combinations, and the retrieve a specific combination. The table will be created once and never be updated. I am using SQLite through JDBC. Is there any simpler way or a best practice to implement such a mapping?
© Stack Overflow or respective owner