O kyrios Phil Endecott egrapse stis Jul 1, 2004 : > >>>in my app i have a table where the id serves as a foreign key for > >>>one or more other tables. if i want to delete a row in the table, > >>>i currently search the other tables where this table is referenced > >>>to see if the row is in use - and then, if not in use, permit > >>>deletion. > >>>Now if i want the delete button in my app to be disabled whenever > >>>a row that is in use is selected, searching the database every time > >>>would dramatically slow down the app.
There's an alternative approach to take. Educate your users to be familiar with PostgreSQL error messages (E.g. ERROR: update or delete on "vessels" violates foreign key constraint "$1" on "certificates" ) > >> > >>Basically you do have to do this search. But it won't be too slow if you > >>create an index on the foreign key. > > > > pity. thought postgres would have some function like 'in_use' to tell when a > > row that is used as a foreign key is in actual use and hence cannot be > > deleted. surely, in a database of millions of records, it wouldnt have search > > them all to find if the row is in use? > > It doesn't "search them all" if you have an index. If your database has > a million records it needs to look at only 20 index entries, as 2^20 is > about a million. (At least that's what I, naively, think it should do - > anyone who knows more want to correct me?) > > --Phil. > > > ---------------------------(end of broadcast)--------------------------- > TIP 7: don't forget to increase your free space map settings > -- -Achilleus ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
