How to check if the KeyValue of a DBLookupComboBox is Nil?
lazarus / 16-Databases

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panoss · 2018-08-05 07:25

How can I check if my combobox 's KeyValue is nil? (null)
The combobox is a DBLookupComboBox.
It 's KeyValue is Variant.

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taazz · 2018-08-05 08:41

Quote from: panoss on August 05, 2018, 09:25:21 amHow can I check if
my combobox 's KeyValue is nil? (null)
The combobox is a DBLookupComboBox.
It 's KeyValue is Variant.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   if
DBLookupComboBox1.keyvalue = null then     showmessage('Nothing was
selected')   else     showMessage('You selected the item with Code
:'+string(DBLookupComboBox1.keyvalue));

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panoss · 2018-08-05 08:52

Thanks it works, my mistake was that I was using 'nil':
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i if
DBLookupComboBox1.keyvalue = nil then 
I thought that nil in Pascal is the null used in other languages.

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taazz · 2018-08-05 09:42

Quote from: panoss on August 05, 2018, 10:52:30 amThanks it works, my
mistake was that I was using 'nil':
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i if
DBLookupComboBox1.keyvalue = nil then 
I thought that nil in Pascal is the null used in other languages.
Null is a variant constant. Since variant is a nullable record in
memory the nil check is against an internal field. But in general you
are correct null and nil are synonyms.

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marcov · 2018-08-05 13:42

Quote from: panoss on August 05, 2018, 10:52:30 amI thought that nil
in Pascal is the null used in other languages.

It is. But you don't want the language pointer NIL, but SQL NULL here.

C NULL and SQL NULL are also two different things.

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ASerge · 2018-08-06 19:00

Quote from: taazz on August 05, 2018, 10:41:29 amCode: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   if
DBLookupComboBox1.keyvalue = null thenVarIsNull is more optimal and
clearer.
This code
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {$MODE
OBJFPC}{$APPTYPE CONSOLE} uses Variants; var  V: Variant; //
Unassigned;begin  if V = null then    ;  if VarIsNull(V) then   
;end.in assembler look like:
Code: ASM  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i # [9] if V
= null then        leaq    -32(%rbp),%rax        movq    %rax,%rcx   
   call    VARIANTS_$$_NULL$$VARIANT        leaq    -32(%rbp),%rdx   
   leaq    U_$P$PROGRAM_$$_V(%rip),%rcx        call   
SYSTEM_$$_equal$VARIANT$VARIANT$$BOOLEAN        testb   %al,%al.Ll7:#
[11] if VarIsNull(V) then        cmpw    $1,U_$P$PROGRAM_$$_V(%rip)  
    seteb   %al        testb   %al,%al