I am having a problem getting a list of fields from a query defined at run time by the users of my program. I let my users enter a SQL query into a memo control and then I want to let them go through the fields that will return and do such things as format the output, sum column values and so forth. So, I have to get the column names so they have a place to enter the additional information.
I would do fine if there were no parameters, but I also have to let them define filter parameters for the query. So, if I want to set the parameters to null, I have to know what the parameter's datatype is.
I am using Delphi 2006. I connect to a Firebird 2.1 database using the DBExpress component TSQLConnection and TSQLQuery. Previously, I was successful using:
for i := 0 to Qry.Params.Count - 1 do Qry.Params[i].value := varNull;
I discovered I had a problem when I tried to use a date parameter. It was just a coincidence that all my parameters up until then had been integers (record IDs). It turns out that varNull is just an enumerated constant with a value of 1 so I was getting acceptable results (no records) was working okay.
I only need a list of the fields. Maybe I should just parse the SELECT clause of the SQL statement. I thought setting Qry.Prepared to True would get me a list of the fields but no such luck. It wants values for the parameters.
If you have an idea, I would sure like to hear it. Thanks for any help.
Replied again 'coz I'm interested. My methods works (with my queries) because they have been pre-defined with the params' datatypes preset to the correct type:)
I'm not sure how you are expecting the query to know or derive the datatype of the param given that you are not even selecting the field that it operates against.
So I think your query setup and user input method will need more attention. I've just looked up how I did this a while ago. I do not use a parameterised query - I just get the "parameter values" from the user and put them directly into the SQL. So your sql would then read:
SELECT s.hEmployee, e.sLastName
FROM PR_Paystub s
INNER JOIN PR_Employee e ON e.hKey = s.hEmployee
WHERE s.dtPaydate > '01/01/2008'
therefore no parameter type knowledge is necessary. Does not stop your users entering garbage but that goes back to input control :)
Although a slightly different dataset type this is what I use with TClientDataset simple and effective :)
for i := 0 to FilterDataSet.Params.Count -1 do
begin
Case FilterDataSet.Params.Items[i].Datatype of
ftString:
ftSmallint, ftInteger, ftWord:
ftFloat, ftCurrency, ftBCD:
ftDate:
ftTime:
ftDateTime:
.
.
.
end;
end;
can you not do something similar with the query?
You guys are making this way too hard:
for i := 0 to Qry.Params.Count - 1 do begin
Qry.Params[i].Clear;
Qry.Params[i].Bound := True;
end;
I'm not sure what version of Delphi you are using. In the Delphi 2006 help under Variant Types, it says:
Special conversion rules apply to the
Borland.Delphi.System.TDateTime type
declared in the System unit. When a
Borland.Delphi.System.TDateTime is
converted to any other type, it
treated as a normal Double. When an
integer, real, or Boolean is converted
to a Borland.Delphi.System.TDateTime,
it is first converted to a Double,
then read as a date-time value. When a
string is converted to a
Borland.Delphi.System.TDateTime, it is
interpreted as a date-time value using
the regional settings. When an
Unassigned value is converted to
Borland.Delphi.System.TDateTime, it is
treated like the real or integer value
0. Converting a Null value to Borland.Delphi.System.TDateTime raises
an exception.
The last sentence seems important to me. I would read that as varNull cannot be converted to a TDateTime to put into the field, and hence you get the exception that you're experiencing.
It also implies that this is the only special case.
Couldn't you do something like:
for i := 0 to Qry.Params.Count - 1 do
begin
if VarType(Qry.Params[i].value) and varTypeMask = varDate then
begin
Qry.Params[i].value := Now; //or whatever you choose as your default
end
else
begin
Qry.Params[i].value := varNull;
end;
end;
What I ended up doing was this:
sNull := 'NULL';
Qry.SQL.Add(sSQL);
for i := 0 to Qry.Params.Count - 1 do begin
sParamName := Qry.Params[i].Name;
sSQL := SearchAndReplace (sSQL, ':' + sParamName, sNull, DELIMITERS);
end;
I had to write SearchAndReplace but that was easy. Delimiters are just the characters that signal the end of a word.
TmpQuery.ParamByName('MyDateTimeParam').DataType := ftDate;
TmpQuery.ParamByName('MyDateTimeParam').Clear;
TmpQuery.ParamByName('MyDateTimeParam').Bound := True;
Related
I have a query that is dynamically set up with a parameter.
I query for lines with a varchar field that contains values that can begin with a '!'.
But I get no match of those.
I use SQLServer as the database server.
If I take the sqlcode and run it directly in the database manager it works but not with TFDQuery.
Se the code example below:
myParameter := '!Tommy';
with qryExec do
begin
SQL.Clear ;
SQL.Add('SELECT * FROM myTable T WHERE T.Name='+quotedStr(myParameter));
active := true ;
first;
if Not Eof then
begin
Result := True;
end;
end; //with
I have no idea what's wrong here, so I would be happy if anyone could come with an explanation.
I would suggest using actual parameters which also avoids the possibility of SQL injection. There are also overloaded versions of Open that reduce the housekeeping lines.
FDQuery1.Open('SELECT * FROM myTable T WHERE T.Name= :NAME',['!Tommy'],[ftWideString]);
I use the following function to search a TStringList I am reading from a file.
I know that when I search a value, then the return value I need is always on the line after the one with the item I search.
It has always worked using POS to search, but now the file has been expanded and I have to look for 2 items 'Adresse' and 'Adresse 2'
That gives me an issue since pos finds 'Adresse' in both cases and my data is then wrong.
Is there another method of searching a string for a substring that I don't know of or do I have to make my own.
function FindValue(const aFilename, aSearch: string): string;
var
InfoList: TStringList;
Counter: integer;
begin
InfoList := TStringList.Create;
try
InfoList.LoadFromFile(aFilename);
if InfoList.Count > 0 then
for Counter := 0 to InfoList.Count - 1 do
begin
if Pos(aSearch, Infolist.Strings[Counter]) > 0 then
Result := Infolist.Strings[Counter + 1]
end
else
Result := '';
finally
InfoList.Free;
end;
end;
For info: the input to the TStringList comes from a textfile extracted from a HTML file.
A sample of a file could be:
OZ8HP
Hugo Pedersen
Radioamatør
Nykøbing M
Sendeposition:
Adresse:
Prinsensvej 18
Postnummer:
7900
Bynavn:
Nykøbing M
Antenne højde (m):
Kote (m):?Kote (m):Brugerens/tilladelsesindehaverens øvrige adresseoplysninger så som Stednavn og/eller Postboks. Hjælpetegnet * kan anvendes, som beskrevet i hjælp.
Koordinater:
Geografisk anvendelse:
Frekvensmaske:
Tekniske specifikationer:
Sendeeffekt basisstation:
Sendeeffekt mobile anlæg:
Båndbredde (MHz):
Antal anlæg:
MMSI:
Kaldesignaltype:
Personlig
Frekvenskategori:
Udstedelses-metode:
Intention om overdragelse:
Nej
Udløbsdato:
Brugerdata:
Brugernummer:
956078
Adresse:
Prinsensvej 18
Adresse 2:
Sejerslev
Postnr.:
7900
Bynavn:
Nykøbing M
Kaldesignal-kategori:
Bestået A
It looks to me as though the real mistake is being too lax in your search. Why accept partial matches? It would seem more robust to look for complete matches
if SameText(aSearch, Infolist[Counter]) then
or perhaps to account for leading and trailing whitespace:
if SameText(aSearch, Trim(Infolist[Counter])) then
You'd need to pass 'Adresse:' or 'Adresse 2:' as the search string, or add the colon in the search function.
Use AnsiSameText if you want locale sensitive comparison. Use = if you want case sensitive comparison, etc.
You might pass multiple search strings and be able to loop only once over the file. As it stands you read it twice which seems wasteful. Indeed surely better to operate on a string list and not be coupled to file storage.
You return the last match in the data rather than the first, for instance. What if there are multiple matches? Does your code behave as intended?
You should also be aware that if no match is found your function does not assign to the Result variable which means it is undefined.
I am trying to build a function/check to prevent wrong inputs from keyboard and I am a little bit lost here.
function ReadInputs : integer;
var
number : integer;
begin
repeat
Write('Set random number (1-10): ');
Readln(number);
if NOT((number <= 10) AND (number >= 1)) then
begin
Writeln('Error! Type 1-10!');
end;
until (number >= 1) AND (number <= 10);
result := column;
end;
How to prevent from any other character to be input except numbers 1-10? Why only numbers define in my function is not enough even when I set integer? When I type for example "A" it crash, so what is the right way? Thank you.
As it stands your program will fail with an error if the user inputs something that cannot be converted to an integer. That's because the variable that you passed to Readln is typed as an Integer. That is effectively an assertion that the user enters a number. But you want to be more flexible than that and allow the user to recover from non-numeric input.
What you need to do is read a string. This will always succeed. Then you can decide how to handle that string. For example you would try to convert to integer, and if that succeeded, perform further validity checks.
Perhaps like this:
var
Input: string;
Num: Integer;
....
Readln(Input);
if TryStrToInt(Input, Num) then
// perform checks on Num, etc.
else
// handle error: the value input was not numeric
You've already had a good answerfrom David H, but a little more explanation might help.
The ReadLn() procedure dates from before applications had GUIs and doesn't really restrict what the user can type in; the user might just press [return] or type characters that aren't digits (or +/-). ReadLn(AnInteger) will succeed if what the user types happens to convert to an integer, otherwise it fails.
On the other hand, Readln(AString) will always succeed, and the problem then is just how to check that it represents an integer, and DH's answer shows you how to do that.
In case you're wondering, a GUI application, you can control what characters an edit control will accept, e.g. by using a TMaskEDit, which allows you specify what character patterns are acceptable (e.g 6 digits and nothing else) - if the user types something which doesn't match the mask, the edit control doesn't accept it. However, even if you use a TMaskEdit, it's best to check that what's been typed in actually converts to the number type you're wanting.
Or you could use this on the OnKeyPress event:
if NOT(key in['0'..'9', #8]) then
key := #0;
I am using (in a Delphi win32 application) OLE to perform search and replace in Word Documents.
THe user prepares a file with some textual tags enclosing them in "{" and "}" and saves the file.
Something like
Dear {NAME},
I want to tell you {WHAT_I_DID_LAST_WEEK}
Of course NAME and WHAT_I_DID_LAST_WEEK are DB fields that can be longer than 255.
So now by using Search and replace with OLE i get a STRING PARAMETER TOO LONG error (it seems 255 is the longest string usable there).
Is there an easy way to get rid of the problem?
Some home made solutons I thought of are:
1) truncate to 255 (good one ;) ) may be appending "..." at the end
2) for every "tag" that requires a replace of more than 255 chars I could first insert more tags like {WHAT_I_DID_LAST_WEEK_1}{WHAT_I_DID_LAST_WEEK_2}{WHAT_I_DID_LAST_WEEK_N} and then replace 255 chars at a time
(1) is a quick solution, at least user doesn't recieve the error, but of course it is not very good
(2) would probably work but it is a workaround, I would prefer another solution.
May be another solution is not use OLE Serach&Replace but use another function.
we use AWordApp.Selection.TypeText(strValue) and loop for replacing tags that have value string longer then 255 chars ...
var
AWordApp: OLEVariant;
...
AWordApp := CreateOleObject('Word.Application');
...
if (Length(strValue) > 255) then
begin
bFound := AWordApp.Selection.Find.Execute(params...);
while bFound do
begin
AWordApp.Selection.TypeText(strValue);
bFound := AWordApp.Selection.Find.Execute(params...);
end;
end;
regards
I am in the need to add additional fields to a TDataSet that don't exist in the underlying database but can be derived from existing fields. I can easily do this with caclulated fields and that works perfectly.
Now I want to edit these fields and write the changed data back. I can reverse the calculation to write the data back into the existing fields, but the DB controls just don't let me edit calculated fields.
Is there any approach that allows me to do this?
Update:
Ok, some more details about the background.
The dataset has a blob field, which is a TBytes representation. Some of the bytes are identified to contain information that can be represented in a convenient way with existing DB edit fields. Not all of the bytes are known, though, so the TBytes representation has to be kept as it is for processing through another application that knows about it. This app also modifies existing and inserts new records.
The TBytes of different records in the dataset often map to different fields representations, although setting a filter or range on the dataset will ensure that they have the same mapping.
As I said, extracting the known bytes and convert it into strings, dates, numbers and so on via calculated fields is no problem. Reconverting those values into the TBytes is also possible. The problem is making those extra fields editable, while keeping the dataset navigation intact.
If it helps: We have classes that do the bidirectional mapping, exposing the fields as published properties.
The answer depends on a data access components you are using. I am using Anydac and it support fkInternalCalc fields, which may be as calculated as manually edited.
I think calculated fields are by definition read-only, with values calculated on the client.
What you want could probably be implemented by an updatable view. You could define the view with calculated fields already - these would be calculated in SQL on the server - and an update trigger, maybe an insert trigger, too - to perform the reverse calculation. Then from the client you could use the view transparently like a table.
I had similar Issue with a ClientDataSet, i have solved this issue using dummy fileds on the SQL-Stmt so i could simulate the Fields in the Database.
See my Question
You can use TDatasetProvider.OnGetRecords (doesn't remember if this is the correct name of the event) and modify the datapacket sent to the Clientdataset.
Of course, you'll have to deal with them on an ApplyUpdates handler, as TOndrej said.
Woll2Woll's infopower components (I just tested their TwwDBEdit) allow to do such thing. So I would think whatever blocks you is at the TDBEdit level (or at the TFieldDataLink level).
What exactly differs in TwwDBEdit, I don't know. (And I'm not sure the license agreement would allow me to post here...).
In our database design, some values are percentages relative to another column (called oMean below), whereas other float values are stored as absolutes. Our customers later wanted both options (rel. and abs.) for all fields, so we came up with the following class derived from TFloatField. It should work for all TDataSet descendants.
unit EditableCalcFloatField;
interface
uses
db, classes;
type
TEditableCalcFloatField = class(TFloatField)
public
oAbs, oRel, oMean: TField;
protected
function GetCanModify: Boolean; override;
procedure SetAsFloat(Value: Double); override;
end;
implementation
function TEditableCalcFloatField.GetCanModify: Boolean;
begin
Result := oMean.AsFloat <> 0;
if not Result then Exit;
Result := (oAbs <> nil) or (oRel <> nil);
end;
procedure TEditableCalcFloatField.SetAsFloat(Value: Double);
var
fMean : Double;
begin
inherited;
if DataSet.State in [dsEdit, dsInsert] then begin
fMean := oMean.AsFloat;
if fMean = 0 then Exit;
if oAbs <> nil then
oAbs.AsFloat := Value / 100 * fMean
else
oRel.AsFloat := Value / fMean * 100;
end;
end;
end.
To use it without a package, you have to create the field in FormCreate, before the dataset is opened:
with TEditableCalcFloatField.Create(Self) do
begin
oAbs := sqlMerkmaleYourAbsoluteColumn;
DisplayLabel := sDisp;
oMean := sqlMerkmaleAssignedValue_Mean;
Calculated := True;
FieldName := 'R' + oAbs.FieldName;
DataSet := sqlMerkmale;
end;
And of course, its contents can be set either in the OnCalcFields event or by the user.
Use a TQuery descendant (MyQuery) with 'Select *, 0 as TempField from MyTable'
Procedure MyQueryAfterOpen(Dataset:TDataSet);
Begin
DataSet.FieldByName('TempField').ReadOnly := False;
End;
It is now an editabe temporary field