How to check if the KeyValue of a DBLookupComboBox is Nil?

[panoss]

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

[taazz]

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

Code: Pascal  [Select][+][-]

1.   if DBLookupComboBox1.keyvalue = null then
2.     showmessage('Nothing was selected')
3.   else
4.     showMessage('You selected the item with Code :'+string(DBLookupComboBox1.keyvalue));
5.  

[panoss]

Thanks it works, my mistake was that I was using 'nil':

Code: Pascal  [Select][+][-]

1. if DBLookupComboBox1.keyvalue = nil then
2.  

I thought that nil in Pascal is the null used in other languages.

[taazz]

Thanks it works, my mistake was that I was using 'nil':

Code: Pascal  [Select][+][-]

1. if DBLookupComboBox1.keyvalue = nil then
2.  

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.

[marcov]

I 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.

[ASerge]

Code: Pascal  [Select][+][-]

1.   if DBLookupComboBox1.keyvalue = null then

VarIsNull is more optimal and clearer.
This code

Code: Pascal  [Select][+][-]

1. {$MODE OBJFPC}
2. {$APPTYPE CONSOLE}
3.  
4. uses Variants;
5.  
6. var
7.   V: Variant; // Unassigned;
8. begin
9.   if V = null then
10.     ;
11.   if VarIsNull(V) then
12.     ;
13. end.

in assembler look like:

Code: ASM  [Select][+][-]

1. # [9] if V = null then
2.         leaq    -32(%rbp),%rax
3.         movq    %rax,%rcx
4.         call    VARIANTS_$$_NULL$$VARIANT
5.         leaq    -32(%rbp),%rdx
6.         leaq    U_$P$PROGRAM_$$_V(%rip),%rcx
7.         call    SYSTEM_$$_equal$VARIANT$VARIANT$$BOOLEAN
8.         testb   %al,%al
9. .Ll7:
10. # [11] if VarIsNull(V) then
11.         cmpw    $1,U_$P$PROGRAM_$$_V(%rip)
12.         seteb   %al
13.         testb   %al,%al