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>Using the ADO Interface</TITLE
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>GNADE User's Guide: GNADE, The GNat Ada Database Environment; Version 1.5.0; Document Revision $Revision: 1.42 $</TH
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>Chapter 22. Using the ADO Interface</H1
><DIV
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><B
>Table of Contents</B
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><DT
><A
HREF="adouse.html#AEN674"
>A Sample Application</A
></DT
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>Building a Sample Application</A
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>Things to know</A
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NAME="AEN674"
>A Sample Application</A
></H1
><P
>      For the communication with the underlying database the application
      uses a so called connection object. The connection object uses
      a so called driver handle in order to communication with the database
      specific driver. The code fragment below shows how to declare a 
      connection to a MySQL data base.
      </P
><PRE
CLASS="PROGRAMLISTING"
>      procedure Client is
         .............
         X  : Driver.Handle := Driver.MySQL.Create;
         C  : Connection.Object(X);
         .............

      </PRE
><P
>      In order to connect to the data base, the Connect method has to be 
      invoked as shown below, where the parameters do depend on the actual
      data base used.
      </P
><PRE
CLASS="PROGRAMLISTING"
>      begin
        ...
        Connect(C, "gnade", Password =&#62; "", Database =&#62; "gnade" );

      </PRE
><P
>      After the connection has been established statements for execution
      may be prepared. In order to do so, the method prepare has to be 
      invoked as shown below.
      </P
><PRE
CLASS="PROGRAMLISTING"
>         -- prepare a query
         S := Prepare( C,
              "select empno, name, firstname from EMPLOYEES " &#38;
              "where empno &#62; :emp and name = :id ;");

         Bind(S, "id", V );
         Bind(S, "emp", E );
      </PRE
><P
>      This method analysis the given statements for so called hostvariables
      and invokes the underlying data base in order to evaluate an execution
      plan.
      </P
><P
>      The following Bind commands connect the hostvariables V and E with the
      host variable names "id" and "emp". The variables V,E are input parameters
      for the query. 
      </P
><P
>      In order to execute the query, the following code fragment is used:
      </P
><PRE
CLASS="PROGRAMLISTING"
>&#13;         -- execute a query
         Value( V, "Bundy" );
         Value( E, 50 );
         R := Execute(C, S );
      </PRE
><P
>      This fragment sets the values of the two hostviariables V and E and 
      executes the statement denoted by S on the connection C. The result 
      of this execution is the result set denoted by the variable R.  
      </P
><P
>      A result set denotes all all records which are generated by the 
      execution of an SQL query statement.
      </P
><PRE
CLASS="PROGRAMLISTING"
>         -- retrieve the result
         declare
            package D_Empname  is
               new String_Domain( Size =&#62; Name_Type'Length, Result =&#62; R, Name =&#62; "name");
            package D_Firstname  is
               new String_Domain( Size =&#62; Name_Type'Length, Result =&#62; R, Name =&#62; "firstname");
            package D_Empno is
               new Integer_Domain( Number_Type =&#62; Empno_Type, Result =&#62; R, Name =&#62; "empno");
         begin
            while not End_Of_Result(R) loop
               Fetch( R );

               Put_Line(Integer'Image(D_Empno.Value) &#38; " " &#38;
                  D_Empname.Value &#38;
                  D_Firstname.Value );
            end loop;
         end ;
         Deallocate( R );
      </PRE
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