How are Queries Interpreted?

Posted on 2002-07-17
Last Modified: 2012-05-04
How does StoryServer return queries for example if

SEARCH TABLE foo INTO t SQL [concat "select * from " $table]
foreach x $t {
 set id [lindex [lindex $x 1] 0]
 set curl [CURL $template $id]
 append f {  } <B>[lindex [lindex $x 1] 1]</B>\n<BR>
Problem is that we are not currently running StoryServer anymore and I am converting TCL code into ColdFusion. So I am trying to understand how TCL works
How does lindex work with queries ?
 Any help would be great!
Question by:DorianP

Accepted Solution

hooker042299 earned 50 total points
ID: 7165152
Here is a fully fleeced out example:

Let's say we have a database like this:

id name
== ====
1  john
2  bill
3  bob

Say we have a bit of code like this:

what happens is that Vignette takes the parameter "x" and creates a hidden variable called "_Schema_x" which is a tcl list containing the order of the columns returned by the SQL - do in this case "id name"

Then into y it places the data returned by the SQL and it places it in a tcl list with a reference to which _Schema_ hidden variable to reference to get the column names.
So, in this example the variable y would contain this:
{x 1 john} {x 2 bill} {x 3 bob}

We could then do something like this:
"foreach z $y {
set id [lindex $z 1]
set name [lindex $name 2]

Returning to your example:
SEARCH TABLE foo INTO t SQL [concat "select * from " $table]
foreach x $t {
set id [lindex [lindex $x 1] 0]
set curl [CURL $template $id]
append f {  } <B>[lindex [lindex $x 1] 1]</B>\n<BR>

Your SQL is being created dynamically based on the value of the variable "table".
Then the "foreach" command is iterating through each row in the variable "t" and assigning that row to the variable "x"

Then, it sets the variable "id" to be the value at position 1 in the row (position 0 will be "foo" in each row - telling internal commands like "FIELD" to look at the hidden variable _Schema_foo as suggested previously).
The outer use of "lindex", "[lindex [lindex $x 1] 0]", rather than just "[lindex $x 1]" suggests that the data returned is itself a list. In the simplified example above, the outer "lindex" would not be necessary.
"set curl [CURL $template $id]" is setting a variable to be a custom url to the path value of variable "template" passing in "id" as the OID.
The line "append f {  } <B>[lindex [lindex $x 1] 1]</B>\n<BR>" confirms that the data returned by the SQL is not as simple as that which I did in my example because there are two elements in it - the id and whatever the developer wants to put in the html in variable "f".

To get a clearer picture, put the command "ERROR_TRACE" or "ERROR_TRACE $x" at various points in the code to understand the values of the various variables set.

Hope this helps.

Author Comment

ID: 7165384
Thanks! This should definitely help me understand.

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