Page 1 of 1
SELECT Command
Posted: Sat Oct 19, 2019 3:31 pm
by Karl-Heinz
Hi Robert,
I´m struggling with the SELECT command.
Code: Select all
#command SELECT <whatever> => dbSelectArea( <(whatever)> )
Something like:
SELECT a becomes dbSelectArea ( "a" )
SELECT 9 becomes dbSelectArea ( "9" )
SELECT 10 becomes dbSelectArea ( "10" ) <-- throws an Exception
VO behaves the same, but Foxpro doesn´t show this problem and selects to workareas > 9. in the DB.prg i see what DbSelectArea() does:
Code: Select all
FUNCTION DbSelectArea(uArea) AS LOGIC CLIPPER ->
FUNCTION _Select(uWorkArea) AS USUAL CLIPPER ->
FUNCTION _SelectString(uWorkArea AS STRING) AS DWORD
My idea is to enhance the _SelectString(). See the KHR comment below
Code: Select all
FUNCTION _SelectString(uWorkArea AS STRING) AS DWORD
LOCAL nSelect := 0 AS DWORD
uWorkArea := AllTrim(uWorkArea)
IF SLen(uWorkArea) = 1
nSelect := Val(uWorkArea)
VAR nAsc := Asc( Upper(uWorkArea) )
IF nAsc > 64 .AND. nAsc < 75
nSelect := nAsc - 64
ENDIF
ELSE
// ------ added KHR
IF NTrim ( Val( uWorkArea ) ) == uWOrkArea
nSelect := Val ( uWOrkArea)
ENDIF
// -------------------
ENDIF
IF nSelect > 0 .OR. "0" == uWorkArea
nSelect := VoDb.SetSelect((INT) nSelect)
ELSE
nSelect := (DWORD) VoDb.SymSelect(uWorkArea)
ENDIF
RETURN nSelect
Now, if _SelectString() processes e.g. "10", the workarea becomes selected. Calling the func with something like "10A" would still fail.
What do you think ?
regards
Karl-Heinz
SELECT Command
Posted: Sat Oct 19, 2019 4:26 pm
by Jamal
Hi Dev Team!
Maybe unrelated, but since we are talking about the SELECT command, the documentation seems incorrect for the SELECT command.
https://www.xsharp.eu/help/command_select.html
Shouldn't the xnWorkArea range be from 0 to 1023 not 0 to 250 ?
VO help has the same doc error. The VO Select() help says it returns a value from 0 to 1023.
Yet, when I scanned X# workareas.prg, I see the:
PUBLIC CONST MaxWorkAreas :=
4096 AS DWORD
Workareas.MaxWorkAreas is used in X# CoreDb.prg:
Code: Select all
STATIC METHOD SetSelect(siNew AS INT) AS DWORD
RETURN CoreDb.Do ({ =>
IF siNew == -1
siNew := (INT) RuntimeState.Workareas:FindEmptyArea(FALSE)
ELSEIF siNEw <= 0
siNew := (INT) RuntimeState.Workareas:FindEmptyArea(TRUE)
ENDIF
IF siNew > Workareas.MaxWorkAreas
siNew := 0
ELSEIF siNew == 0
RddError.PostArgumentError( __FUNCTION__, EDB_SELECT, nameof(siNew), 1, <OBJECT>{siNew})
ELSE
RuntimeState.CurrentWorkarea := (DWORD) siNew
ENDIF
RETURN (DWORD) siNew
})
Now this is confusing! Which/What is correct?
Jamal
SELECT Command
Posted: Sat Oct 19, 2019 4:53 pm
by robert
Jamal,
Sabo always used to say (with a fat German accent) "ze truz is in ze source".
So the maximum value is 4096.
Robert
SELECT Command
Posted: Sun Oct 20, 2019 6:10 am
by Karl-Heinz
Hi Jamal,
the first workarea of a dbServer is 4096, the next is 4095, etc.
the workarea of a classic server depends on what you´re doing.
Code: Select all
RddSetDefault ( "dbfcdx" )
SetExclusive ( FALSE )
cDbf := "d:testsmall.dbf"
oDB := DbServer { cDBF }
? oDB:WorkArea // 4096
? DbGetSelect() // 4096
?
oDB := DbServer { cDBF }
? oDB:WorkArea // 4095
? DbGetSelect() // 4095
?
DbSelect ( 0 ) // <------------
use (cDBF) alias "one"
? DbGetSelect() // 1
?
oDB := DbServer { cDBF }
? oDB:WorkArea // 4094
? DbGetSelect() // 4094
?
DbSelect ( 0 ) // <------------
use (cDBF) alias "two"
? DbGetSelect() // 2
When you deactivate both DBSelect(0) calls you´ll see how dangerous it is to use a mixture of dbservers and classic servers. The million Dollar question: If both Dbselect(0) calls are deactivated, which servers are finally in the shown workareas ?
regards
Karl-Heinz
SELECT Command
Posted: Sun Oct 20, 2019 2:37 pm
by Jamal
Hi Karl-Heinz,
Yes, I see how that mix can be a problem.
Jamal
SELECT Command
Posted: Sun Oct 20, 2019 3:15 pm
by robert
Karl-Heinz,
The default behavior if the DbServer class is to not restore the current workarea after an operation.
You can call DbSetRestoreWorkarea(TRUE) to tell the DbServer class to restore the workarea after an operation.
That is "cleaner" but slightly slower, at least that was the case in VO. I am really not sure if this is still the case in X#.
And in stead of DbSelect(0) I would recommend to use the NEW clause for the USE command. This guarantees that the file will be opened in a new workarea.
Robert