Populating a TDbGrid
lazarus / 16-Databases

----------------------------------------------------------------------
hac3ru · 2014-02-23 12:14

Hello,

I have the following code:
Code: [Select]procedure TForm1.Button2Click(Sender: TObject);
var count : integer;
    i     : integer;
begin
  count := 0;
  Form2 := TForm2.Create(self);
  Form2.Datasource1.DataSet := SQLQuery1;
  Form2.DBGrid1.DataSource := Form2.Datasource1; 
  SQLQuery1.SQL.Text:= 'SHOW columns FROM testtable';
  SQLQuery1.Open;
  While not SQLQuery1.EOF do
  begin
    Form2.DBGrid1.Columns.Add;
    Form2.DBGrid1.Columns.Items[count].Title.Caption :=
SQLQuery1.Fields[0].AsString;
    Inc(count);
    SQLQuery1.Next;
  end;
  SQLQuery1.Close;
  SQLQuery1.SQL.Text := 'SELECT * FROM testtable';
  Form2.Datasource1.Enabled := True;
  SQLQuery1.Open; 
  Form2.ShowModal;
  Form2.Free;
  SQLQuery1.Close; The problem is that the DbGrid is not written
correctly. I see the number of entries (if the Db has 7 entries I get
7 empty fields in the Grid). I checked to see if the datasource is
correctly populated with Code: [Select]While not SQLQuery1.EOF do
  begin
    Memo1.Lines.Add(Form2.Datasource1.DataSet.Fields[0].AsString);
    Memo1.Lines.Add(Form2.Datasource1.DataSet.Fields[1].AsString);
    Memo1.Lines.Add(Form2.Datasource1.DataSet.Fields[2].AsString);
    SQLQuery1.Next;
  end;        This returned the values from the datasource which seem
to be the ones in the Database so the Datasource is written
correctly.... Anyone any ideas?

----------------------------------------------------------------------
taazz · 2014-02-23 13:55

1) dbgrid does not require you to add the columns manually, simple
opening a linked dataset should auto populate the columns collection
with all the columns returned by the query using the field's name as
column title.
2) you do not link the columns to the required fields eg Code:
[Select]DBGrid1.Columns.Items[0].FieldName :=
SQLQuery1.Fields[0].AsString.

----------------------------------------------------------------------
hac3ru · 2014-02-23 17:20

Quote from: taazz on February 23, 2014, 02:55:23 pm1) dbgrid does not
require you to add the columns manually, simple opening a linked
dataset should auto populate the columns collection with all the
columns returned by the query using the field's name as column title.
2) you do not link the columns to the required fields eg Code:
[Select]DBGrid1.Columns.Items[0].FieldName :=
SQLQuery1.Fields[0].AsString.

That's what I did first and it didn't work so I manually added the
columns. Data in teh Dataset is correct. The DBGrid is not showing it
though.

----------------------------------------------------------------------
wp · 2014-02-23 17:42

Fields[0].AsString? That's the field value of the current record. I am
pretty sure that you should use "Fields[0].FieldName" instead.

----------------------------------------------------------------------
taazz · 2014-02-23 17:50

I assume that the command "SHOW columns FROM testtable" will return
the fields of  testTable as values in the rows having multiple columns
based on the field information eg fields[0] is the field name
fields[1] is the datatype etc. You have to make sure that the
fieldname gets the value of the field's name not data type or anything
else that might get returned by the sql command. As for the details of
what is returned I will leave it to people that use MYSQL to answer it
personally I stay away from MySQL at all cost.

----------------------------------------------------------------------
wp · 2014-02-23 19:10

QuoteI assume that the command "SHOW columns FROM testtable" will
return the fields of  testTable as values in the rows Ah - I must
confess that I did not read the first posting...

----------------------------------------------------------------------
mangakissa · 2014-02-24 10:30

look at option 1 from taazz.
DBGrid only works with a datalink to a dataset. And why using the
datacomponent again if you want to see the first dataset.
if this code
Code: [Select]count := 0;
  Form2 := TForm2.Create(self);
  Form2.Datasource1.DataSet := SQLQuery1;
  Form2.DBGrid1.DataSource := Form2.Datasource1; 
  SQLQuery1.SQL.Text:= 'SHOW columns FROM testtable';
  SQLQuery1.Open;
//  SQLQuery1.Close;
//  SQLQuery1.SQL.Text := 'SELECT * FROM testtable';
//  Form2.Datasource1.Enabled := True;
//  SQLQuery1.Open; 
  Form2.ShowModal;
  Form2.Free;
  SQLQuery1.Close;

----------------------------------------------------------------------
taazz · 2014-02-24 16:37

Quote from: hac3ru on February 23, 2014, 06:20:03 pmQuote from: taazz
on February 23, 2014, 02:55:23 pm1) dbgrid does not require you to add
the columns manually, simple opening a linked dataset should auto
populate the columns collection with all the columns returned by the
query using the field's name as column title.
2) you do not link the columns to the required fields eg Code:
[Select]DBGrid1.Columns.Items[0].FieldName :=
SQLQuery1.Fields[0].AsString.

That's what I did first and it didn't work so I manually added the
columns. Data in teh Dataset is correct. The DBGrid is not showing it
though.

What did you do first? allow the dbgrid to auto populate its columns?
For me it does work and it is easy to check. Add all components to a
form (connection, dataset, datasource, dbgrid etc) link them togethere
add the "select * from testTable" on the query-dataset and then open
the connection and activate the dataset does the dbgrid show the
columns? If not please create a basic sample witch shows the problem
and I"ll take a closer look.