check if a datasource has a dataset
lazarus / 16-Databases

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Hansvb · 2016-01-18 21:37

How can i check if a datasource has a dataset?

I want to turn a filter of but get an error because there is no
DBGrid.DataSource.DataSet
So if there is no active DBGrid.DataSource.DataSet then there is no
need of turning of the filter.

i tried this:
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
Frm_Main.Active_DBGrid.DataSource.DataSet.Active = true then     
begin        aDBGrid.DataSource.DataSet.Filtered:=False; //filter uit
zetten

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wp · 2016-01-18 22:32

Check for Datasource.Dataset <> nil, or Assigned(DataSource.Dataset):

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
Assigned(DBGrid1.DataSource.Dataset) and
DBGrid1.Datasource.Dataset.Active then   
DBGrid1.DataSource.DataSet.Filtered := False;
And don't compare boolean values against true or false. The "if" needs
only a boolean value to work with, DataSet.Active is enough. If you
compare against true you just create another boolean value which is
already there. And what would prevent you from applying the comparison
with true a second time, or another time...:

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
((Dataset.Active = true) = true) then ...//orif
((((((Dataset.Active=true) = true) = true) = true) = true) = true)
then ... You see the nonsense in there?

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Hansvb · 2016-01-19 20:10

i was looking at the wrong place. I had to check: 

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
Assigned(DBGrid1.DataSource) and (DBGrid1.Datasource <> nil) thenbegin
... end;
Now it is working.

I see you're point with:

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
((Dataset.Active = true) = true) then ...
I have to change a lot of if's.

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wp · 2016-01-19 20:55

Quote from: Hansvb on January 19, 2016, 09:10:45 pmCode: 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
Assigned(DBGrid1.DataSource) and (DBGrid1.Datasource <> nil) thenbegin
... end;
Both conditions do exactly the same, drop one of them (http://lazarus-
ccr.sourceforge.net/docs/rtl/system/assigned.html). But maybe you also
want to  check for an existing Dataset:

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
Assigned(DBGrid1.DataSource) and Assigned(DBGrid1.Datasource.Dataset)
then