Seeking coding example for TSQLTimeStamp - mysql

Question

Delphi XE2 and MySql.
My previous question led to the recommendation that I should be using MySql's native TIMESTAMP datatype to store date/time.
Unfornately, I can't seem to find any coding examples, and I am getting weird results.
Given this table:
mysql> describe test_runs;
+------------------+-------------+------+-----+---------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------+-------------+------+-----+---------------------+-------+
| start_time_stamp | timestamp | NO | PRI | 0000-00-00 00:00:00 | |
| end_time_stamp | timestamp | NO | | 0000-00-00 00:00:00 | |
| description | varchar(64) | NO | | NULL | |
+------------------+-------------+------+-----+---------------------+-------+
3 rows in set (0.02 sec)
I woudl like to :
declare a variable into which I can store the result of SELECT CURRENT_TIMESTAMP - what type should it be? TSQLTimeStamp?
insert a row at test start which has start_time_stamp = the variable above
and end_time_stamp = some "NULL" value ... "0000-00-00 00:00:00"? Can I use that directly, or do I need to declare a TSQLTimeStamp and set each field to zero? (there doesn't seem to be a TSQLTimeStamp.Clear; - it's a structure, not a class
upadte the end_time_stamp when the test completes
calcuate the test duration
Can somene please point me at a URL with some Delphi code whcich I can study to see how to do this sort of thing? GINMF.

Answer 1

I don't know why you want to hassle around with that TIMESTAMP and why you want to retrieve the CURRENT_TIMESTAMP just to put it back.
And as already stated, it is not a good advice to use a TIMESTAMP field as PRIMARY KEY.
So my suggestion is to use this TABLE SCHEMA
CREATE TABLE `test_runs` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`start_time_stamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`end_time_stamp` timestamp NULL DEFAULT NULL,
`description` varchar(64) NOT NULL,
PRIMARY KEY (`id`)
);
Starting a test run is handled by
INSERT INTO test_runs ( description ) VALUES ( :description );
SELECT LAST_INSERT_ID() AS id;
and to finalize the record you simply call
UPDATE test_runs SET end_time_stamp = CURRENT_TIMESTAMP WHERE id = :id

Answer 2

just declare a TSQLQuery (or the correct component for the data access layer of your choice), attach it to a valid connection and populate it's SQL property with:
select * from test_runs;
double click on the query to launch it's fields editor and select add all fields from the contextual menu of that editor.
It will create the correct field type, according to the data access layer and driver you're using to access your data.
Once that's done, if you need to use the value in code, usually you do it by using the AsDateTime property of the field, so you just use a plain TDateTime Delphi type and let the database access layer deal with the specific database details to store that field.
For example, if your query object is named qTest and the table field is named start_time_stamp, your Delhi variable associated with that persistent field will be named qTeststart_time_stamp, so you can do something like this:
var
StartTS: TDateTime;
begin
qTest.Open;
StartTS := qTeststart_time_stamp.AsDateTime;
ShowMessage('start date is ' + DateTimeToStr(StartTS));
end;
If you use dbExpress and are new to it, read A Guide to Using dbExpress in Delphi database applications

Answer 3

I don't know about MySQL, but if the TField subclass generated is a TSQLTimeStampField, you will need to use the type and functions in the SqlTimSt unit (Data.SqlTimSt for XE2+).
You want to declare the local variables as TSQLTimeStamp
uses Data.SQLTmSt....;
....
var
StartTS: TSQLTimeStamp;
EndTS: TSQLTimeStamp;
begin
StartTS := qTeststart_time_stamp.AsSQLTimeStamp;
SQLTmSt also includes functions to convert to and from TSQLTimeStamp, e.g. SQLTimeStampToDateTime and DateTimeToSQLTimeStamp.
P.S. I tend to agree that using a timestamp as a primary key is likely to cause problems. I would tend to use a auto incrementing surrogate key as Sir Rufo suggests.