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M:M table conditional delete for parents

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Postgresql 8.1.4 on Redhat 9

I have a table which stores M:M relationships. I can't put foreign keys to the parents of this table because the relationships being stored go to several tables. This was done so that only two fields have to be searched in order for all relationships to be found for an item. For an oem number there might be 50 to 100 relationships and 40 different tables having to do with materials, locations, revisions, specifications, customer, etc. that might be referenced.

Is there some way I can make a mock foreign key restraint on the parents so the parent would search the M:M table for  a matching value in key1 if the relate-key is 22, 23, 25 or 100 before it allows the row to be deleted?

relate-key        relate-type                key1        table1        key2         table2
22                product-material        23        oem        545        material
22                product-material        23        oem        546        material
23                product-engine                23        oem        15        engine
25                product-stage                23        oem        3        stage
100                product-revision        23        oem        2270        specifications


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Margaret Gillon, IS Dept., Chromalloy Los Angeles

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