re: column ambigously defined / table alias

[Rainer Döbele]

Hi Pascal,

 

if you want to join with the same table twice then you need to create a second 
instance of that table.

Also if you want to do a self join on a table.

 

This is approximately how to do it:

 

public TTableA           T_TABLEA1;

public TTableA           T_TABLEA2;

public TTableB           T_TABLEB;

 


T_TABLEA1 = new TTableA();

T_TABLEA2 = new TTableA();

T_TABLEB = new TTableB();

 

cmd.join(T_TABLEA1.C_ID_A, T_TABLEB.C_ID_A, DBJoinType.INNER);

cmd.join(T_TABLEA2.C_ID_A, T_TABLEB.C_ID_A, DBJoinType.LEFT);

 

Empire-db generates a different alias for every instance of TTableA and thus 
give you the result you are expecting.

Regards
Rainer

 

from: T-Rex [mailto:trex...@googlemail.com] 
to: empire-db-user@incubator.apache.org
re: Re: column ambigously defined / table alias

 

Hello Rainer,

thanks for the fast answer.
The generated SQL will be something like that:

SELECT *
FROM 
 TableA t1 INNER JOIN TableB t2
  ON t1.id_a = t2.id_a  
  LEFT JOIN TableA t1
    ON t1.id_a = t2.id_a

In our application there are more joins and some where clauses which require 
the left join here...
As you can see the table alias t1 has to be different at the second join to get 
that statement working.

Regards,

Pascal

2010/8/17 Rainer Döbele <doeb...@esteam.de>

Can you give us the sql that has been generated?

(you may call cmd.getSelect() to get it)

 

Regards

Rainer

 

 

from: T-Rex [mailto:trex...@googlemail.com] 

to: empire-db-user@incubator.apache.org

re: column ambigously defined / table alias

 

Hello empire-db community,

in our application we've got a similar problem like the given example below.
We build a command object with different joins depending on different 
expressions.

As you can see we have an inner join and a left outer join on the same tables.
If we execute the statement we get the exception: column ambiguously defined.
>From our point of view the framework is not able to set the table aliases on 
>it's own if required and
we do not have the possibility to set the alias manually.

Furthermore we see not the possibility to create a full outer join.

Example:
###################################################

public class PROJECTDB extends DBDatabase
{
    public TTableA           T_TABLEA;
    public TTableB           T_TABLEB;

    public static class TTableA extends DBTable
    {
        // Spaltendefinitionen
        public final DBTableColumn  C_ID_A;
        public final DBTableColumn  C_VALUE_A;
        public final DBTableColumn  C_ID_C;
    ...
    }
    public static class TTableB extends DBTable
    {
        // Spaltendefinitionen
        public final DBTableColumn  C_ID_A;
        public final DBTableColumn  C_VALUE_B;
    ...
    }


...

}

public class DO_SOME_THING 
{

...

    public method_B (DBCommand cmd)
    {
        cmd.join  (PROJECTDB.TTableA.C_ID_A, PROJECTDB.TTableB.C_ID_A, 
DBJoinType.INNER);
    }

    public method_C (DBCommand cmd) 
    {
        cmd.join  (PROJECTDB.TTableA.C_ID_A, PROJECTDB.TTableB.C_ID_A, 
DBJoinType.LEFT);
    }

..

    public method_A 
    {
        DBCommand  cmd = ...;

        if (expressionX()) {
        method_C(cmd);
        }        

        if (expressionY()) {
        method_B(cmd);
        }        
...
        readValuesFromDB(cmd);
...

    }
###################################################

Do you have any clues?

Regards,

Pascal