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Remove 0.96 for update to 0.98
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Bruce Momjian
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.61 [en] (X11; I; Linux 2.2.11 i586) [Netscape]">
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</head>
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<body text="#000000" bgcolor="#FEFEDF" link="#0000EF" vlink="#51188E" alink="#FF0000">
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<h1>
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FORMS</h1>
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<hr WIDTH="100%">
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<p>This version (0.97) of PgAccess has changed the form API : variable
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handling, query results interface and control bindings naming convention.
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Please read it carefully, download the database demo and practice a while
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before trying to design your own forms.
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<p>For the moment, it has only some basic widgets : labels, entries, buttons
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, listboxes , checkboxes and radiobuttons.
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<p>Also there is a pseudo data control widget that allows you yo have access
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to a query results.
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<p><b>How do you generate widgets :</b>
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<ol>
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<li>
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select a widget from the toolbox by clicking the appropriate radiobutton</li>
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<li>
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move to the canvas , point with the mouse at the desired location and click
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the mouse button to begin</li>
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<li>
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keeping the mouse-button pressed move the mouse in order to draw a rectangle
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that will hold the widget</li>
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<li>
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release the mouse-button</li>
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</ol>
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In the rectangle that you have designed it will appear the selected object.
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<br>Move now to the attribute window to change some of its properties.
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<p>Renaming, resizing items are possible (for the moment) only by modifying
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appropriate parameters in attribute window. You <b>must </b>press Enter
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in the edit field after changing a value in order to be accepted.
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<p>You can also move items by dragging them or delete them by pressing
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Del key after selecting them.
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<p>In attribute window, there are some fields named <b><tt><font size=+1>Command
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</font></tt></b>and
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<b><tt><font size=+1>Variable</font></tt></b>.
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<p>The field <b><tt><font size=+1>Command </font></tt></b>have meaning
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only for Button widgets and holds the command that will be invoked when
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the button is pressed.
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<p> The field <b><tt><font size=+1>Variable </font></tt></b>have
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meaning only for EditField , Label widgets , checkboxes and radiobuttons
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and it is the name of the global variable that will hold the value for
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that widget. For checkboxes the values are <b>t</b> and <b>f</b> (from
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true and false) in order to simplify binding to logical data fields (PgAccess
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0.82 used 0 and 1).
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<p> For radiobuttons, it is usual to assign the same
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variable to the same radiobuttons within the same group. That variable
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will contain the name of the widget of the radiobutton that has been pressed.
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Let's presume that you have entered 3 radiobuttons named red, green and
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blue, all of them having the same variable named color. If you will press
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them, they will assign their names to global variable.
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<p> In order to make a simple test, put an entry field
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and set it's variable to <b>v1</b> and a button who's command is "set v1
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whisky". Press the button "Test form" and click on the button. In that
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entry should appear whisky.
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<br>Another test is defining in Script module a script called "My first
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script" having the following commands:
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<br><tt><font size=+1>tk_messageBox -title Warning -message "This is my
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first message!"</font></tt>
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<br>and then define a button who's command is <b><tt><font size=+1>execute_script
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"My first script"</font></tt></b>.
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<br>
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<h2>
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Database manipulation</h2>
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Let's presume that our form have the internal name <b><tt>mf </tt></b>(<b>m</b>y
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<b>f</b>orm). Don't forget that the Tk window names could not start with
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an uppercase letter.
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<br>The window will be referred inside the Tcl/Tk source as <b><tt>.mf</tt></b>
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<br>If you want to close the form in run-time you have to issue the command
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<b><tt>destroy
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.mf</tt></b>
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<p>Also, any widget created inside this window (form) will have the name
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prefixed by <b><tt>.mf ,</tt></b>so we will have <b><tt>.mf.button1</tt></b>
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or <b><tt>.mf.listbox1</tt></b> .
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<p>We can name the data control widget <b><tt>dc</tt></b> for example.
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The fully qualified name for that "virtual widget" will be <b><tt>.mf.dc</tt></b>
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then. A new namespace called <b><tt>DataControl(.mf.dc)</tt></b> will be
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automatically defined.
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<br>The <b><tt>Command </tt></b>property of the data control widget must
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contain the SQL command that will be executed.
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<br>When the form will be in run-time, automatically you will have access
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to the following procedures and functions from the namespace:
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<p><b><tt>open</tt></b> - opens the connection and execute the query (returns
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nothing)
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<br><b><tt>setSQL newsql</tt></b> - set the command query that will be
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executed at the next <b><tt>open</tt></b>
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<br><b><tt>getRowCount</tt></b> - returns the number of records of the
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result set
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<br><b><tt>getRowIndex </tt></b>- returns the current record number inside
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the result set
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<br><b><tt>getFieldList</tt></b> - returns a Tcl list containing the fields
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names from the current result set
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<br><b><tt>moveFirst</tt></b> - move the cursor to the first record in
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the recordset
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<br><b><tt>moveLast</tt></b><tt> , <b>moveNext</b> , <b>movePrevious</b></tt>-
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moves the cursor there
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<br><b><tt>moveTo newrecno</tt></b> - move the cursor to that new record
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number (first is 0)
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<br><b><tt>updateDataSet</tt></b> - update the variables inside the designed
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form that have a particular name (I'll explain later)
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<br><b><tt>clearDataSet</tt></b> - clear the associated DataSet variables
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<br><tt><b>fill listbox field</b> </tt>- fill the named listbox (whole
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widget name as <b><tt>.mf.listbox1</tt></b>) with the all the values of
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that field from the current result set
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<br><b><tt>close</tt></b> - close the result set (<b><font color="#FF0000">if
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you don't close it, you will loose some memory</font></b>)
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<p>These procedures and functions should be called in the normal Tcl namespace
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mode as in the following example:
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<p><tt>DataControl(.mf.dc)::setSQL "select * from phonebook"</tt>
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<br><tt>DataControl(.mf.dc)::open</tt>
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<br><tt>set nrecs [DataControl(.mf.dc)::getRowCount]</tt>
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<p>If you complaint about writting to many DataControl(...) you can include
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many commands into a single namespace eval as in the following example
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:
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<p><tt>namespace eval DataControl(.mf.dc) {</tt>
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<br><tt> setSQL "select * from phonebook"</tt>
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<br><tt> open</tt>
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<br><tt> set nrecs [getRowCount]</tt>
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<br><tt> moveLast</tt>
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<br><tt> updateDataSet</tt>
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<br><tt>}</tt>
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<p>It's no need to close a query-result set if you want to assign it a
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new SQL command and open it again. That will be done automatically releasing
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the memory used for the last result set.
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<br>Opening a new <b>DataControl</b> will automatically position the current
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row index of the result set on the first row (index 0) and will define
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a new global associative array named <b>DataSet</b> that will hold data
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from the current row. The key into that array will be the fully qualified
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name of the data control widget followed by a comma and the name of every
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field in the selected rows.
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<p><i>Example:</i>
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<br><tt>DataSet(.mf.dc,name)</tt>
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<br><tt>DataSet(.mf.dc,city)</tt>
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<p>If you want to bound some controls to the fields of the recordset, you
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will have to name their associate variable like that :
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<p><b><tt>DataSet(.mf.dc,salary)</tt></b> to get the "salary" field , or
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<b><tt>DataSet(.mf.dc,name)</tt></b> to get the "name" field. Using the
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data control procedures <b><tt>DataControl(.mf.dc)::moveNext</tt></b> or
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movePrevious will automatically update the <b><tt>DataSet(.mf.dc,...)</tt></b>
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array so the database information from entries in the form will be refreshed.
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<br>
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<p>Here it is a dumped <b><a href="formdemo.sql">sample database</a></b>
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that contains a demo database. What should you do ?
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<br>Shift-click the above URL in order to download that tiny file (4 Kb).
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Create a empty database and <b><tt>psql yourdatabase <formdemo.sql</tt></b>
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<p>You should find a single table called "phonebook" a form called "Phone
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book" and another "A simple demo form".
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<p>First of all enter and view the phonebook table in table view. Note
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the fields and their values.
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<br>Open the "Phone book" form and enter a letter (a, e or i) in the field
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to the left of "Find" button then press Find. It's fine to enter one letter
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in order to get more records in query result. You will get information
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about the number of records selected, in the listbox you will see all the
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values of field "name" from the current data set. Use buttons to move to
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first, next, previous or last record within the record set.
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<p>In order to add a new record, press the "New" button in order to get
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new, clean entries. Fill them with your data and press "Add new" button.
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A new phonebook record will be added. Also, if you want to update a record,
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change it's values in the displayed fields after finding it and press "Update"
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button. The values will be updated in the database BUT NOT IN THE CURRENT
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QUERY RESULT . If you want to see them modified, make a new query trying
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to find it again.
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<p><font color="#000080">Before using the results from a query you should
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know that the information that has been retrieved could be found only in
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your computer client memory. It has <b>no live connection</b> to the data
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from the database. That's why it isn't possible to develop a simple update
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function as interface to that query-result widget. More than that : a query
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result could be obtained from a SQL command that return a non-updatable
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data set !!! For example fields gathered from multiple tables or summary
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fields. It isn't just simple to make an automatic update procedure. The
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programmer must know how to make the update or the append procedure, sometimes
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using key fields to point to the desired record or an OID. There are examples
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in the demo database in "Phone book" form. It may be possible that in the
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future, I will develop another pseudo-widget describing a table. It would
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be more simple than to implement an update or append or even a delete procedure.</font>
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<p>There is in the demo database also another simple form called "A simple
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demo form". It will show you how to handle variables from checkboxes, radiobuttons,
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how to use listboxes, open another forms and so on. I think they will help
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you.
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<p>In order to avoid naming user defined forms with a particular
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name of another PgAccess form, I would recommend naming them as udf0, udf1
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(user defined form 0 , 1 )
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<p>
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<hr WIDTH="25%">
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<p>Please feel free to send me your opinion at <b>teo@flex.ro</b> on forms
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designing and usage.
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<p><b><font size=+1>KEEP IN MIND !
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THE FORM API MAY CHANGE IN ORDER TO BE MORE SIMPLE AND BETTER!</font></b>
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<br><b><font size=+1>SEND ME YOUR WISHES, YOUR IDEAS, YOUR OPINIONS !</font></b>
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<br><b><font size=+1>ALSO ... DON'T BLAME ME IF YOU WILL HAVE TO RE-DESIGN
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YOUR OLD FORMS DUE TO SOME INCOMPATIBILITIES WITH NEWER PGACCESS VERSIONS.</font></b>
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</body>
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</html>
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