2013/8/29 silvioprog <silviop...@gmail.com>
> 2013/8/29 Michael Van Canneyt <mich...@freepascal.org>
>
>> On Thu, 29 Aug 2013, silvioprog wrote:
>>
>> Hello,
>>> I'm trying to do something with a dataset, but I think that isn't
>>> possible.
>>>
>>> Assuming I have the following table:
>>>
>>> create table users (
>>> id serial not null primary key,
>>> email varchar(100),
>>> nickname varchar(20) not null
>>> );
>>>
>>> And the following records:
>>>
>>> id | email | nickname
>>> 1 | us...@domain.com | user1
>>> 2 | us...@domain.com | user2
>>> 3 | us...@domain.com | user3
>>>
>>> I want to clear the email of the second user, but using parameters:
>>>
>>> id | email | nickname
>>> 1 | us...@domain.com | user1
>>> 2 | <null> | user2
>>> 3 | us...@domain.com | user3
>>>
>>> But when I try this:
>>>
>>> SQLQuery1.SQL.Add('update users set email = :email');
>>> SQLQuery1.SQL.Add('where id = :id');
>>> SQLQuery1.ParamByName('id').**AsInteger := 2;
>>> SQLQuery1.ParamByName('email')**.Clear;
>>> SQLQuery1.ExecSQL;
>>> SQLTransaction1.Commit;
>>>
>>> I got:
>>>
>>> "Project project1 raised exception class "EDatabaseError" with message:
>>> PQConnection1: Unknown fieldtype for parameter "email"."
>>>
>>> I know that I could solve easily via literal string, but I need to use
>>> parameters anyway.
>>>
>>> How I solve this?
>>>
>>> Here in Brazil, a friend suggested this:
>>>
>>> VParam := SQLQuery1.ParamByName('email')**;
>>> VParam.DataType := ftString;
>>> VParam.Clear
>>>
>>> Is this the only way? '-'
>>>
>>
>> Yes and no.
>>
>> In 2.6.2 this is the only way.
>>
>> There is a fix in SVN that allows you to simply do clear, and it will use
>> then the "any"
>> field type of postgres (or something similar).
>>
>> Michael.
>
>
> I'll try the trunk version. Thank you very much Michael! (y)
>
Other interesting feature is the property EmptyAsNull:
http://docwiki.embarcadero.com/VCL/XE/en/IBCustomDataSet.TIBStringField.EmptyAsNull
It tests if field (ftString) is empty (f = ''), if yes, it set the field
value to null (f.Clear).
--
Silvio Clécio
My public projects - github.com/silvioprog
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