Macro variables

EhLib TeamLess than 1 minute

Macro variables in SQL expressions SQLDataDriverEh.XXXCommand

SQL expression in SQLDataDriverEh commands (ADODataDriver, DBXDataDriver, ...) can contain Macro variables. Before executing the SQL statement the Macro variables are replaced by the values assigned to them and actual SQL statement is formed, which is transmitted for execution.

For example the expression “select * from %table_name%” contains a macro variable "%table_name%". If this variable contains the value of "Country", a real expression that will be transferred to the execution will be the next 'select * from Country'.

You can type in SQLDataDriverEh.SelectSQL, UpdateSQL, DeleteSQL, InsertDQL, GetrecSQL commands any expression that may contain a combination of SQL statements and macro variables.

In the collection of the elements SQLDataDriverEh.MacroVars.Macros it is necessary to create macro- elements and give them names according to the variables inscribed in the SQL command.

At design-time you can enter the values of macro variables, or leave them blank.
At run-time before the opening MemTableEh connected to SQLDataDriverEh you can set the value of the macro variable:

ADODataDriverEh1.SelectSQL.Text := ‘select * from %table_name%’
ADODataDriverEh1.MacroVars.Macros['%table_name%'] := ‘Country’;
MemTableEh1.Open;
…
if Conditions 
  then ADODataDriverEh1.MacroVars.Macros['%table_name%'] := ‘table1’
  else ADODataDriverEh1.MacroVars.Macros['%table_name%'] := ‘table2’;

Use SQLDataDriverEh.FinalSelectSQL, FinalUpdateSQL, FinalInsertDQL, FinalGetrecSQL properties to access the actual SQL expression.

Demo: See a Demo project of using macro variables in the folder of the library – <EhLib Dir\Demos\DataDriver.Macros>