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Table, index and multiple relations
Message
De
18/02/2005 21:15:25
Hilmar Zonneveld
Independent Consultant
Cochabamba, Bolivie
 
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Versions des environnements
Visual FoxPro:
VFP 8
Divers
Thread ID:
00988168
Message ID:
00988543
Vues:
70
This message has been marked as a message which has helped to the initial question of the thread.
>Hi Hilmar,
>
>Yes I'm familiair with queries and have used them a lot.

OK. In this case, views should be easy for you.

First, the basic idea: A view is, in essence, an "updatable query": while a query is read-only, a view can be made updatable. As soon as you save your data, the changes are updated in the underlying tables.

While a query (built with the query designer) is stored in a file with extension .QPR, a view is easiest to manage if it is part of a database.

  • Open a project.
  • Select (or create) a database.
  • Expand the database in the project manager, and select "Local Views".
  • Click on the button "New...", and then select "New View".
  • Now, you enter the view definition window. This is almost identical with the query manager, which you say that you already know. Add your tables, relate them, etc. For a first test, select all fields from a single table.
  • To make your view updatable, go to "Update Criteria". In the field list, activate the column with the key icon, for your primary key (this must be a column that has a different value for each record). Activate the column with the pencil icon, for all other columns. Warning: if the primary key is not defined correctly, the wrong records can be updated.
  • Click on "Send SQL updates". This is a "master switch": if you forget this, no data will be updated.
  • Save and close the view. It will be saved in your database. I recommend that you give the view a name that starts with "lv_" (for "local view"). If the view is based mainly on a table called "client", call the view "lv_client".

    To use the view:
  • Make sure the database, which contains the view, is open (open database...).
  • Open the view like a table, for example: use lv_client.
  • Do some changes.
  • Select your preferred buffering mode (usually 3 or 5). Again, this is just like working with a table.
  • Save the changes, and see if the changes were applied to the original table.

    In many aspects, you work with the view just as if it were a normal table (with buffering enabled). For example, you can make changes with REPLACE, add records with APPEND BLANK, save changes with TableUpdate(), or undo changes with TableRevert().

    HTH,

    Hilmar.
    Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
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