Imagine this table format, and let's kind of go with the notion that these are records for actual keys:

Table: key
Fields:
    id - Unique identifier for each key.
    opens - id of device the key opens.  We're assuming a many-to-one
            relationship but that could be many to many by adding anot
+her
            table mapping which targets share the same key.
    available - 0 or 1.
    date_created
    checkout_date
    user_id
    due_date

[download]

Next you would have a table, key_history:

Table: key_history
    id - unique history id.
    key_id - maps to the id of the key.
    action - created, checked-out, checked-in, destroyed.
    date_added
    user_id

[download]

Now whenever someone needs a key you can start a transaction, find a key that matches available=1, and opens=$target, and update that key to have the correct current user id, available=0, checkout_date = now, due_date = now + 7d. And at the same time make an entry in the history table. Use a transaction to assure that nobody else grabs the same key at the same time, and to allow for rollback if it turns out that the key has become unavailable.

Check-in should fail loudly if it tries to happen to a key id that already is checked in. Also, in this model each key has a unit of one. If you need more than one key that opens the same door, you would have multiple rows. And each user either tracks which key he has, or the application tracks it for him.


Dave

In reply to Re: Searching Database Question by davido
in thread Searching Database Question by htmanning

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.