How to bulk copy the values from a TSQLQuery record to a TdxMemData record? - sql

Question

Just to make it clear, I do not want to copy the entire TSQLQuery into the TdxMemData, as I would use memds.CopyFromDataSet(qry) for that.
I am interating through each record from the TSQLQuery, and I may or may not be adding a record(s) to the TdxMemData. Generally the record in memds matches that in qry, but sometimes the values are altered and sometimes additional records are added to memds. My example did not make this clear since all it seemed to do was copy over each record.
So given an active record in the TSQLQuery, I want to copy over the values into an active editable record in the TdxMemData.
The following code works in so far as it creates a copy of the record:
qry := TSQLQuery.Create(nil);
memds := TdxMemData.Create(nil);
try
qry.SQLConnection := cn;
qry.Text := 'SELECT Field1, Field2, Field3 FROM Table1';
qry.Open
memds.CreateFieldsFromDataSet(qry);
memds.Open;
while not qry.Eof do
begin
if {some condition} then
begin
memds.Append;
for i := 0 to qry.FieldCount-1 do
memds.Fields[i+1].Value := qry.Fields[i].Value; //First field is RecID
//Do something with the current memds record
end
else if {some other condition} then
begin
memds.Append;
//change values
memds.Append;
//change values
memds.Append;
//change values
end
else if {a third condition} then
; //Skip any work on memds
qry.next;
end;
qry.Close;
//Do something with memds
memds.Close;
finally
memds.Free;
qry.Free;
end;
Is there a better way? I had looked at AppendRecord but creating the array of TVarRec doesn't seem to be straightforward.
EDIT:
Let's use these examples with very simplified criteria. Note that the actual conditions that determine how many records to append and the changes to the field values in the destination are complex and not in any database.
Method 1:
While not tblSource.Eof do
Begin
If (iCondition = 1) Then
Begin
// Add one record
tblDestination.Append;
tblDestination.FieldByName('Field1').Value := tblSource.FieldByName('Field1').Value;
tblDestination.FieldByName('Field2').Value := tblSource.FieldByName('Field2').Value;
tblDestination.FieldByName('Field3').Value := tblSource.FieldByName('Field3').Value;
tblDestination.FieldByName('Field4').Value := tblSource.FieldByName('Field4').Value;
tblDestination.FieldByName('Field5').Value := tblSource.FieldByName('Field5').Value;
if bSomethingCondition then
tblDestination.FieldByName('Field4').Value := 'Something';
End
Else If (iCondition = 2) Then
Begin
// Add two records
tblDestination.Append;
tblDestination.FieldByName('Field1').Value := tblSource.FieldByName('Field1').Value;
tblDestination.FieldByName('Field2').Value := tblSource.FieldByName('Field2').Value;
tblDestination.FieldByName('Field3').Value := tblSource.FieldByName('Field3').Value;
tblDestination.FieldByName('Field4').Value := tblSource.FieldByName('Field4').Value;
tblDestination.FieldByName('Field5').Value := tblSource.FieldByName('Field5').Value;
if bAnotherThingCondition then
tblDestination.FieldByName('Field4').Value := 'Another thing';
tblDestination.Append;
tblDestination.FieldByName('Field1').Value := tblSource.FieldByName('Field1').Value;
tblDestination.FieldByName('Field2').Value := tblSource.FieldByName('Field2').Value;
tblDestination.FieldByName('Field3').Value := tblSource.FieldByName('Field3').Value;
tblDestination.FieldByName('Field4').Value := tblSource.FieldByName('Field4').Value;
tblDestination.FieldByName('Field5').Value := tblSource.FieldByName('Field5').Value;
if bSomethingElseCondition then
tblDestination.FieldByName('Field4').Value := 'Something else';
End
Else If (iCondition = 0) Then
Begin
// Add no records
End;
tblSource.Next;
End;
Since the number of fields in the source and destination tables can vary, hard-coding field names as in Method 1 is not suitable.
Method 2:
While not tblSource.Eof do
Begin
If (iCondition = 1) Then
Begin
// Add one record
tblDestination.Append;
for i := 0 to tblSource.FieldCount-1 do
tblDestination.Fields[i+1].Value := tblSource.Fields[i].Value;
if bSomethingCondition then
tblDestination.Fields(iSomethingConditionFieldIndex).Value := 'Something';
End
Else If (iCondition = 2) Then
Begin
// Add two records
tblDestination.Append;
for i := 0 to tblSource.FieldCount-1 do
tblDestination.Fields[i+1].Value := tblSource.Fields[i].Value;
if bAnotherThingCondition then
tblDestination.Fields(iAnotherThingConditionFieldINdex).Value := 'Another thing';
tblDestination.Append;
for i := 0 to tblSource.FieldCount-1 do
tblDestination.Fields[i+1].Value := tblSource.Fields[i].Value;
if bSomethingElseCondition then
tblDestination.Fields(iSomethingElseConditionFieldIndex).Value := 'Something else';
End
Else If (iCondition = 0) Then
Begin
// Add no records
End;
tblSource.Next;
End;
While method 2 above does work, and is the way it is currently done, this question is whether there is a way to pass the variant array of field values from tblSource to tblDestination using AppendRecord.
Instead of this:
// Add one record
tblDestination.Append;
for i := 0 to tblSource.FieldCount-1 do
tblDestination.Fields[i+1].Value := tblSource.Fields[i].Value;
if bSomethingCondition then
tblDestination.Fields(iSomethingConditionFieldIndex).Value := 'Something';
Do this:
tblDestination.AppendRecord({tblSource fields var array);
if bSomethingCondition then
tblDestination.Fields(iSomethingConditionFieldIndex).Value := 'Something';
Of course, it might be that there is no answer, and that the method I currently employ is the best solution.

Answer 1

Try the following
Query1.Open();
dxMemData1.AddFieldsFromDataSet(Query1);
dxMemData1.Open;
dxMemData1.LoadFromDataSet(Query1);

Answer 2

Creating an array of TVarRec isn't difficult, and AppendRecord may indeed help. The following code adds a record to a TClientDataSet (named CDS for brevity) that has 4 fields of type string, float, boolean, and string in that order:
CDS.AppendRecord(['Smith', 123.45, False, 'Test text']);
Note that you have to create a value for every single field (column) in the dataset, in the order that they exist in the FieldDefs collection, or you'll get an exception.
(Of course, the real question is why you're returning extra rows and iterating through them, instead of testing the conditions in your SQL statement WHERE clause and only returning the rows you actually need. This can almost always be done using parameters.)

Answer 3

If you don't want to use AddFieldsFromDataSet -> LoadFromDataSet , and want to load fields and records manually, you also can do it. You can create fields programmatically and append records by iterations. Look example:
MD.Fields.Clear;
MD.FieldDefs.Clear;
MD.Close;
with MD.FieldDefs.AddFieldDef do
begin
Name := 'UserID';
DataType := TFieldType.ftInteger;
CreateField(MD);
Name := 'GridName';
DataType := TFieldType.ftString;
Size := 255;
CreateField(MD);
Name := 'TemplateGrid';
DataType := TFieldType.ftBlob;
CreateField(MD);
end;
MD.Close;
MD.Open;
MD.Append;
MD.FieldByName('UserID').AsInteger := 1;
MD.FieldByName('GridName').AsString := Self.Name
TBlobField(MD.FieldByName('TemplateGrid')).LoadFromStream(LStream);
MD.Post;
You can easily modify it to load fields with names and types from your dataset as they are.