How To Get And Set Dbaddress In Reports

Commands using database addresses give you the ability to mark a record when running a report. You can return directly to the record later in the report and print it. The address can be used to navigate through lists and control what is displayed.

This feature is useful right now for the Web Host but will likely find other uses. Database addresses can be used in the following ways.

- print a database address
- store it in a variable
- set the current database address from a variable or an absolute number
- set the 'starton' database address for a loop
- set the 'fallback' database address to help with end-of-list scenarios
- set the database address plus or minus some number of records.
- retrieve and print the record at a particular database address

The following snippet illustrates the syntax of these commands in a loop retrieving a client's active accounts.

//begin code snippet
@cl.de NO TOTAL where (@de.mo = Active) max = 40
@starton = @vardbaddr+@varadvance
@fallback = @varfallbackdbaddr
@vardbaddr& = @de.dbaddress
@varfallbackdbaddr& = @de.dbaddress if (@tvarCtr = 0)
@tvarNothingFound = " "
@tvarCtr = @(tvarCtr+1)
@de.na<25> @de.ac< @de.li< @de.pr<15.0> @de.ow<15.0> @de.sta<
@cl.de
//end code snippet

In this snippet:

@starton gets the database address for the first record in a loop.

SYNTAX: @starton = <dbaddress>
EXAMPLE: @starton = @de.dbaddress

The @starton command must be the next line after beginning a loop.

Example from code snippet:
@cl.de NO TOTAL where (@de.mo = Active) max = 40

@starton = @vardbaddr+@varadvance

@varadvance is used to scan ahead or backwards through lists.

SYNTAX: @varadvance

Example from code snippet:

@starton = @vardbaddr+@varadvance

@fallback is used when the user clicks Next and there is nothing more to return. Without the fallback address, Collect! displays the last record in the list. The fallback address should be the first item of the list displayed.

SYNTAX: @fallback = <dbaddress>
EXAMPLE: @fallback = @de.dbaddress

Example from code snippet:

@fallback = @varfallbackdbaddr
@varfallbackdbaddr& = @de.dbaddress if (@tvarCtr = 0)

@vardbaddr& assigns a dbAddress to a variable. The ampersand (&) indicates a dbAddress type variable.

SYNTAX: @<vardbaddr>& = @<form>.dbaddress
EXAMPLE: @vardbaddr& = @de.dbaddress

Example from code snippet:

@vardbaddr& = @de.dbaddress
@varfallbackdbaddr& = @de.dbaddress if (@tvarCtr = 0)

Advanced Syntax

The @SET command sets the dbaddress to a selected record and reads the record from the database, making its contents current for subsequent printout.

SYNTAX: @SET<form>.dbaddress
EXAMPLE: @SETde.dbaddress

You can perform simple addition and subtraction on dbaddresses to make the Collect! report system read ahead or back by some number.

SYNTAX: @SET<form>.dbaddress+99
EXAMPLE: @SETde.dbaddress+99

Other examples:
@SETde.dbaddress-99
@SETde.dbaddress+@<var>

SYNTAX: @starton = <form>.dbaddress+99
EXAMPLE: @starton = de.dbaddress+99

Other examples:
@starton = de.dbaddress;-99
@starton = de.dbaddress+@<var>

99 represents a numeric, any number between -99 and 99 will do.

Using These Commands In A Sample Report

To use these examples, create a blank report and paste the following commands into your new report body and run the report.

Assign the dbaddress of the Debtor form to the variable varAddr and print them both.

@varAddr& = @de.dbaddress
Variable: @varAddr
Direct: @de.dbaddress

Now we'll loop through the debtors and print a couple of names. Note that by the end of this loop the current debtor will be the last one printed in the loop and the dbAddr variable will contain the dbaddress of the last one printed.

@de max = 2
@varAddr = @de.dbaddress
@de.na @varAddr
@de

Here is a loop using the starton. This loop will start on the last one printed during the previous loop, and will print from there.

@de max = 10
@starton = @varAddr
@de.na @varAddr
@de

Here is a loop using starton and fallback. Fallback address is set as the dbaddress of the first item in a list.

@de max = 10
@starton = @varAddr
@fallback = @varFallback
@varFallback = @varAddr
@de.na
@de

Here is a loop using starton plus a fixed number of records (3 in this case).

@de max = 10
@starton = @varAddr+3
@fallback = @varFallback
@varFallback = @varAddr+3
@de.na
@de

Here is a loop using starton and moving back a number of records specified in the variable varCount.

@varCount = -10
@de max = 10
@starton = @varAddr+@varCount
@fallback = @varFallback
@de.na
@de

Web Host Implementation

Implementing this on Web host is a bit of a trick but it's simple enough, once you understand what it is doing. The variables varAddr, varFallback and varCount are submitted to the Collect! Web Host from the browser. When the report runs, it fills in these variables for the current instance of the report and sends that data to the browser.

By doing things this way, we support the general HTTP concept that the server is stateless and merely responds to individual requests, rather than keeping track of where the user is at any point in time. The form displayed on the client's browser contains all the information necessary to pursue the client objectives. The submit command is formulated to pass that data to the server and all is well.

This method gives us great flexibility while conforming to internationally recognized standards.

Security

If a person constructs a web page and attempts to enter their own dbaddresses to selectively scan your database, they will have a hard time. The dbaddress is encoded in a special way to detect tampering. If they attempt to use a bad address, then Collect! can do one of two things, depending on what the report command was.

If the command was @SET and the address is bad, then Collect! clears the record data being searched on. Attempting to print any data from that record results in zeros and invalid data.

If the command is @starton, it means it is in a list, and if the address is bad, then the system returns an empty list. Nothing is printed in the list. It is as if no records exist.

Address Encryption

Security is a consideration for Web Host. You don't want someone constructing a web page and then testing to see what data they can get. Therefore the dbaddress is encoded to be functional for only one given ID and only one specific session for that ID, and to detect tampering. An invalid or altered dbaddress is not acted upon and the event is written to the Collect! Application Log.