• Add Fields to List Dialog Box
• Alpha Five Basics
• Automatic Backup and Revision Control of Layouts and Field Rules
• Automatically Populating Linking Field Values when Doing Data Entry
• Calculated Fields
• Calculated Values
• Changing the Caseof Words
• Coded Fields
• Controlling a Field's Width
• Copy Previous Field
• Creating a Field Rule Event
• Creating a Posting Field Rule
• Creating a Simple List
• Creating and Using a Summary Field
• Creating and Using an Email Smart Field
• Creating and Using Calculated Values
• Data Field Control Properties
• Default Values
• Defaulting a Date Field to Today's Date
• Define an Alpha Five View Query
• Dial Phone Number in Field
• Display Help Topic
• Exporting Fields from a Table
• Expression Builder
• F1 Context Sensitive Help
• Field Rule Field Events
• Field Rule Record Events
• Field Rules
• Field Rules Table Lookups
• Field Rules: Field Types
• Filtering Records to Exclude a Single Field Value
• Find Tables that Contain a Field Name
• Form Level Field Rules
• How Auto-Increment Fields Work
• Improvements V9
• List Box Table Lookup
• Mask Style
• Microsoft Word Integration
• Modifying a Form Field on the On Change Event
• Multi Field Quick Filter Dialog Box
• Override Field Definitions Dialog
• Overview of Field Rules
• Parent-Child Dialog Example
• Placing a Calculated Value on a Form
• Placing a Data Field on a Form
• Placing Bitmap and JPEG Image Fields
• Placing Image File Reference Fields
• Placing Smart Fields on a Form
• Query Builder
• Quickly Sorting and FilteringRecords
• Re-EvaluatingField Rules
• Recalculating Calculated Fields
• Required Fields
• Resize Fields to Fit Data
• Retrieving Distinct Field Values
• Returning a Different Field Than You Display
• Right-Click Menus
• Select Fields Dialog - Generic
• Select Text in a Field
• Skipping Over Fields
• Sorting and Selecting Overview
• Specify Filter Dialog
• Specify Order Dialog
• Specify Table Name Dialog
• Tracking Changes to Table Fields
• Types of Field Rules
• Update Example
• Using a Coded Lookup Field
• Using Field Rules to Generate A Table Lookup
• Using Field Statistics
• Using Object Properties for Table Lookups
• Using the Fields Panel
• Validation Rules
• When Calculated Fields are Calculated
• Xbasic View Record

Tracking Changes to Table Fields

Description

This topic describes a general technique for tracking when fields in different tables are modified. The technique uses:

• two global variables

• a logging table

• two functions for writing and reading log entries

• field rules for identifying when field values change

• event scripts that retrieve update information

The following screen shows the technique implemented for a set with two tables.

The Record_ID field on the form shows the value of the Record_ID global variable, which also happens to be the value of the current record's unique ID field. The TStamp field on the form shows the value of the TStamp global variable, which is the last updated date and time value for the current field.

The Logging Table

The fieldlog logging table has the following structure.

• Fieldname

  Type: C, Width: 50, A combination of the table and field name. For example:

  Order->Description.

• Stamp

  Type: C, Width: 25, Large enough to contain the expression "" + now().

• Rec_ID

  Type: C, Width: 8, Large enough to hold the unique ID associated with each record. Presumably, all tables' IDs are the same length.

Global Variables

The following variables are defined in the autoexec script. The Record_ID variable contains the unique ID associated with the currently selected record. The TStamp variable contains the last updated date time value associated with the current field.

dim global Record_ID as C
dim global TStamp as C

Field Rules

Attach the following script to the CanWriteField event of each field that you want to log. The following example is associated with the Description field of the Order table.

if (A_FIELD_VALUE <> Order->Description) then
    loggit("Order->Description")
end if

Logging Functions

The loggit() function adds and updates records in the fieldlog logging table.

FUNCTION loggit as V ( fld as C )
dim t as P
dim q as P
dim c as N
t = table.open("fieldlog")
query.filter = "Fieldname = " + s_quote(fld) + " .and. Rec_ID = " + s_quote(var->Record_ID)
q = t.query_create()
c = q.records_get()
if ( c = 0 ) then
    t.enter_begin()
    t.Fieldname = fld
    t.Stamp = "" + now()
    t.Rec_ID = var->Record_ID
    t.enter_end(.t.)
else
    t.fetch_first()
    t.change_begin()
    t.Stamp = "" + now()
    t.Rec_ID = var->Record_ID
    t.change_end(.t.)
end if
query.filter = .T.
q.close()
t.close()
END FUNCTION

The readlog() function retrieves the last updated value for the currently selected field.

FUNCTION readlog as V (fld as C )
dim t as P
dim q as P
on error goto norec
t = table.open("fieldlog")
query.filter = "Fieldname = " + s_quote(fld) + " .and. Rec_ID = " + s_quote(var->Record_ID)
q = t.query_create()
t.fetch_first()
var->TStamp = t.stamp
query.filter = .T.
q.close()
t.close()
end
norec:
resume next
END FUNCTION

Form Field Event Scripts

Each form field that is logged has a script similar to the following that is under its OnArrive event. This example is for the Description field of the Order table. The Order_ID field is the unique ID field for the parent Order table.

var->Record_ID = Order->Order_ID
record_id.refresh()
readlog("Order->Description")
tstamp.refresh()

Embedded Browse Event Script

Each embedded browse has a script similar to the following that is under its OnRowChange event. This example is for the Description field of the Item table. The Item_ID field is the unique ID field for the child Item table.

var->Record_ID = Item->Item_ID
record_id.refresh()
readlog("Item->Description")
tstamp.refresh()