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Hi,
I want to use a relational database to store data that is nested and
where the order is preserved. I am having a hard time wrapping my head
around how to do the following mostly because I don't have much
experience with relational databases.
I am looking at mapping a structure like so:
<node id="1">
<node id="11">
<node id="111">
<node id="1111"/>
<node id="1112"/>
<node id="1113"/>
</node>
<node id="112"/>
<node id="113"/>
<node id="114"/>
</node>
<node id="12">
<node id="121"/>
<node id="122"/>
<node id="123"/>
</node>
</node>
To a relational database that might have a table representing it like:
Node
-------
id
parentId
parentIndexPosition
First question: Is using an index position the best way to maintain the
position? (or is preceding and/or following sibling better? or something
else?)
OK, lets say I have imported some data/XML into the above table, giving
appropriate parents and index positions.
Next, say I want to move /node/node[2]/node[@id=121] to the position
/node/node[1]/node[1].
How do you handle updating the index position of other nodes? All
children of /node/node[@id=12] will need their parentIndexPosition moved
down one. And all children of /node/node[@id=11] will need their
parentIndexPosition moved up one. (the ID attributes where abritrarily
created and should not indicate position)
Is there a built in mechanism to do this type of thing in relational
databases? If not how would an UPDATE look?
Are there any java libraries or articles out there that handle this type
of thing? (I am having a hard time finding anything with google)
thanks,
-Rob
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