DATETIME PLZ
lazarus / 16-Databases

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hinst · 2014-04-25 15:37

If I retrieve a field of type DATETIME using AsString property, will
the db library then convert it to TDateTime and then to string, or
will it extract it directly as string?

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marcov · 2014-04-25 17:55

In general TDatetime probably.

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LacaK · 2014-04-25 18:23

@hinst: can you provide more details about your question. Which DB,
which client library, which client database components ?

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hinst · 2014-04-25 18:43

I am having in mind sqldb aka fcl-db, I use no visual components, I do
things in code
TField has properties: AsString and AsDateTime
I suppose that sqldb receives date as string, then converts it to
TDateTime. Then AsString property perhaps does not convert TDateTime
to string, but provides the string as is instead
I currently work with MySQL database

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engkin · 2014-04-25 18:57

TField.AsDataTime is going to raise an exception:
Code: [Select]function TField.GetAsDateTime: TDateTime;
begin
  raise AccessError(SdateTime);
end;

While TDateTimeField and TDateField would trust you and read raw data
into @Result:
Code: [Select]function TDateTimeField.GetAsDateTime: TDateTime;
begin
  If Not GetData(@Result,False) then
    Result:=0;
end;

As for TStringField, it does convert String to TDateTime:
Code: [Select]function TStringField.GetAsDateTime: TDateTime;
begin
  Result:=StrToDateTime(GetAsString);
end;

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mangakissa · 2014-04-26 06:38

Quote from: hinstI suppose that sqldb receives date as stringIt
depends how your date is saved in your table. If it is a datetime
field, it will be saved as double. Retreaving the date via SQLdb will
be convert with AsDateTime or AsString. Even .AsFloat should work.
If the date is saved as a string, the conversing could probably fail
if the format is not correct.

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hinst · 2014-04-26 08:57

So MySQL sends date as Double, in FPC TDateTime is Double, but
encodings differ?

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LacaK · 2014-04-26 10:53

If we are speaking about MySQL then:
- MySQLConnection calls MySQL client library API to get result row
data. In current implementation this row data are returned as PChar so
MySQLConnections translated "string representation" of DateTime into
TDateTime (double)
- This TDateTime value is stored in local record buffer maintained by
TBufDataSet (TSQLQuery)
- When you request Field.AsDateTime then this value is simply moved as
is
- When you request Field.AsString then  this value is simply moved as
is + FormatDateTime() is used

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hinst · 2014-04-26 11:02

I see. I was hoping that original string representation of datetime
returned by MySQL API is stored