Three experiences of developing database program with Delphi

1. Establishment of temporary tables

Data input is the necessary link of developing database program. In a client/server structure, a client may have to enter a batch of data and then submit it to the server's back-end database, which requires a temporary data table to be set up locally (the client) to store data entered by the user, and the local table data is purged when submitted. The advantage of this method is that it improves the input efficiency and reduces the network burden.

Because the amount of data that a user enters at once is small (no more than hundreds of records), a temporary table can be built in memory, which is handled faster.

Method 1: Use the query control (tquery)

1th step: Put the Query Control (tquery) on the form and set up the connected datasheet.

2nd step: Make Tquery. Cachedupdates=true;

Tquery. Requestlive=true

Step 3rd: Add a WHERE child statement after the original SQL statement, asking that the SQL query result be empty after adding the where child statement.

For example:

　　SELECT Biolife.″Species No″, Category, Common_Name, Biolife.″Species Name″, Biolife.″Length (cm)″, Length_In, Notes, Graphic
　 　 FROM ″biolife.db″ Biolife
　　 where Biolife.Category=′A′ and Biolife.Category=′B′

So the temporary table is completed.

Method 2: Create a temporary table using code

The code is as follows:

　　function CreateTableInMemory(const AFieldDefs:TFieldDefs):TDataSet;
　　 var
TempTable:TClientDataSet;
　　 begin
　　 TempTable:=nil;
　　 Result:=nil;
　　 if AFieldDefs$#@60;$#@62;nil then
　　 begin
　　 try
　　 TempTable:=TClientDataSet.Create(Application);
　　 TempTable.FieldDefs.Assign(AFieldDefs);
　　 TempTable.CreateDataSet;
　　 Result:=(TempTable as TDataSet);
　　 Except
　　 if TempTable$#@60;$#@62;nil then
TempTable.Free;
　 Result:=nil;
　　 raise;
　 　 end
end
　 end;

Use the following methods in your program:

　　procedure TForm1.Button1Click(Sender: TObject);
　　 var
ADataSet:TDataSet;
　　 begin
　　 ADataSet:=TDataSet.Create(Self);
　　 with ADataSet.FieldDefs do
　　 begin
　　 Add(′Name′,ftString,30,False);
　　 Add(′ ue′,ftInteger,0,False);
　　 end;
　　 with DataSource1 do
　　 begin
　　 DataSet:=CreateTableInMemory(ADataSet.FieldDefs);
　　 DataSet.Open;
　　 end;
　　 ADataSet.Free;
　　 end;

temporary table creation completed.

Method 1 is simple to use, but because of the query control, you need to query the server back-end database for the data, so it's a bit slow and does not apply to the fact that the fields in the temporary table are pieced together by fields from several data tables. Method 2 is wide and fast, but requires coding. (The use of Tfielddefs in code is very simple, see Delphi online Help).