TDBComboBox showing only one row?
lazarus / 16-Databases

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tatamata · 2007-06-11 16:42

Hello.
Lazarus 0.9.22, Windows XP, PostgreSQL 8.2., ZEOS components.
TDBComboBox is driving me crazy!
I just can't figure out how to get all rows from table into the
combobox list. It always shows only one value (the first record), and
I can't retrieve other values. If I drop-down, the list is empty.
When I navigate through the same dataset, by using TDBGrid,
TDBComboBox changes it's current value, respectively. But the list is
empty, whenever I drop down the combobox. So, it seems that
TDBComboBox is behaving like a textbox, showing always only current
record's value.
Is this a bug, or I am clumsy?

Regards,

Zlatko

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DougNettleton · 2007-06-11 18:47

Zlatko:

Are you aware that you have to fill in the "Items" that will appear in
the drop down list?  I just tried it with MySQL 5.0 connection, a
SQLTranaction, a SQLQuery, a DataSource, a DBComboBox and a
DBNavigator, using last night's snapshot for windows 32-bit and it
works as I expected.

HTH,

Doug

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tatamata · 2007-06-11 20:07

Hi, Doug.
No, I didn't know that I have to set Items, if I have already
connected TDBComboBox to a dataset, by setting DataSource and
DataField properties of the combobox. I thought it would be similar to
TDBGrid...
What exactly should I enter in Items TStringList?
I tried to put a table field name, but a string appears as an item in
combobobx. That's not what I want to accomplish. Basically, I want all
values of a particular field of a dataset to be represented as
combobox values in dropdown list, so that I can choose a value (item)
and the dataset cursor goes to the corresponding row.
Can it be done by setting items property, or I need to fill items
through code?

Thanks,

Zlatko

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DougNettleton · 2007-06-11 21:41

Zlatko:

You can fill the items with code, but this may not what you want do. 

Assume you have a person table with several address fields - one of
which is province / state - I'm in North America.  You may want to
have a separate table with State / Province code and their
corresponding description.  As you browse through your "person table"
you may want to look-up their province / state code and display the
description and use the pull-down list to allow selection by the user
friendly description.  If this is the functionality you want, you want
a DBLookupComboBox.  This is not currently impemented in Lazarus as
far as I know.

Years ago in the pre- 15Meg program days, I used to be amazed that
there wasn' a component in Delphi that worked like a combnation of a
DBRadioGroup and a DBComboBox - so you could have say a marital
status:

S - Single
M - Married
D - Divorced
W - Widow(er)
U - Unknown

You'd define the "items" Single / Married / Divorces / Widow(er) /
Unknown and "Values" S / M / D / W / U like a DBRadioGroup but the
display would only take up 1 line like a DBComboBox unless you clciked
the drop down arrow.  Internally, you'd store the 1 character codes
and present to the user the friendly description.

Such a control, you could "load with code" for small static lookup
tables, but alas ...

HTH,

Doug

P.S. if you successfully create your own DBLookupComboBox don't be
shy.  It would be a welcome additon to Lazarus.

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tatamata · 2007-06-12 04:56

Oh, it seems that I completely misunderstood DBComboBox behavior!
I thought that combobox READS items from Datasource/DataField, while
it actually WRITES TO DataField/DataSource from items! (I was
searching in some books this sleepless night, to clarify this to
me:)).
That's because I'm currently switching from MS Access, where combobox
behaves in both ways. It can be used both from reading from and
writing to a field in a table. It could be similar to DBLookupCombo, I
think. I was using this dual behavior of comboboxes in Access for fast
jumping to a row in a form's recordset (instead of iteration), by
synchronizing form's recordset with combobox recordset. (recordset
cloning, bookmarks etc.). It needed only several lines of code.
I suppose it is possible to get such behavior by some hard-coding in
Lazarus (someone suggests me some direction?).
Regarding creating DBLookupComboBox, hm, hm, hm, I wish I was so smart
to be able to do that, but my current knowledge is so, so, limited:).

Best regards,

Zlatko