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Relate Multiple Table IDs to Single Column ID

Posted on 2010-09-03
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Last Modified: 2012-05-10
Ok, I have a rather large relational database I'm building and have run into a problem relating tables to each other.  I need to relate an ID in one table to several other tables.  And this occurs several times.  I'm going to give a fictitious example to try and reflect what I'm doing.

I have a large number of assets which are all very unique with their own properties.  For example, Apples, Oranges, Bananas, and Grapes.  Tied to each of these are Images and Reports.  So I have a table for each asset, which each has an ID number which is a GUID.  The Images table houses all the images, the Reports table houses all the reports.

Now what I'm looking for is this.  What is the best practice for linking the Images and Reports back to the individual asset?

Right now what I've setup is an AssetID in both the Images and Reports table which points to the ID number of the asset owner.  The problem is I have no idea which asset table this ID comes from, it could be from Apples, Oranges, Bananas or Grapes.  With Images this isn't that big of a deal as I only lookup images coming from the Asset-to-the-Image.  For reports this is a problem though.  For reports I have to go from Reports-to-Assets.  The report will vary depending on whether it's for an Apple, Orange, Banana, or Grape.  

I need to be able to do queries on the reports table and then generate reports based on the asset they come from.  Obviously I can setup a stored procedure to loop through the asset tables and find the correct asset, etc.  But is there a better way to do this?

My understanding is that a GUID is always unique, so using one ID column to reference multiple table IDs shouldn't be a problem as far as unique IDs are concerned.  

I could setup a ReportToAsset table that contains ReportID, AssetID, AssetType (the name of the asset table, Apple, Orange, etc.).  To me though this seems just as precarious as what I have setup now... unless there is a way to setup a hard relationship between the asset tables and the ReportsToAssets table.  Is this possible?

So, database experts, what's the best way to solve this?  I'm looking for a solution that can directly relate the record to the proper table.  The solution could be in many forms, an altered table structure, or with a fancy SQL query that figures out the correct relationship.

If I were to delete a report I cannot currently setup a relationship to automatically cascade and delete the asset associated with that report.  I would have to do it manually with code.  What is the standard practice in this sort of information structure?
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Question by:aj2010
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by:Ephraim Wangoya
ID: 33598279
You can set them up as
Asset Table
AssetID, AssetDescription

Report Table
AssetID, other report fileds

Image Table
AssetID, AssetImage

From such a structure, you can use joins to obtain any information you want. Also set up tour referencial integrities. Deleting a report should not affect the asset, however deleting an asset should cause the cascade deletion of the reports and images for that asset
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Author Comment

by:aj2010
ID: 33601944
I do not follow your suggestion.  Again, I have multiple assets.  As an example four tables, Apples, Oranges, Bananas, and Grapes.

So I have a Apples.ID, Oranges.ID, Bananas.ID, and Grapes.ID - all uniqueidentifier/GUID

In your suggestion how does Images.AssetID and Reports.AssetID reference the asset table it goes with?  How can I setup a constraint that will cascade and delete a report/image if a record in one of the asset tables is deleted?
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Accepted Solution

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aj2010 earned 0 total points
ID: 33711895
I guess nobody had any suggestions.  I solved this problem myself.  What I did was create an Asset table, and then a child table for each type of asset, for example, Asset_Apples, Asset_Oranges, Asset_Bananas, Asset_Grapes, etc.

The Asset table has an Id = GUID.  Each of the child assets likewise have Id = GUID.  The child tables relate to the Asset table as foreign key.  In code my class objects derive from asset, for example, Apple :: Asset.  Inside the Reports and Images table I reference the Asset.Id.
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