what is "Key class" in Entity Bean of EJB ?

[gk]

Hi, I have 4 questions ....i have made it in a interactive way and
tried to explain in simple way.

do you have answer ?



what is "Key class" in Entity Bean of EJB ?

you might say, for each primary key/field of a table, there should be
a class , and its a "Key class"

am i right ?

Q1 :

If so, there are so many fields in a table apart from the primary
field.

why we dont make the classes for those ? we only make a class
for Primary filed ? why ?
is it because when we pull by keywe will get value ?
or any other reason also ?

Q2:
how this primary Key class is used in the Entiyty bean ?

Q3:
can we make 2 Key class ? can we use these 2 in the Entity Bean ?

Q4: i have a column say ALPHA and has the values say A,B,C etc in 3
rows respectively.

how do i make a Key class for such column type carrying these values ?


Regards

 

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

what is "Key class" in Entity Bean of EJB ?

you might say, for each primary key/field of a table, there should be
a class , and its a "Key class"

am i right ?
Yes.

Q1 :

If so, there are so many fields in a table apart from the primary
field.

why we dont make the classes for those ? we only make a class
for Primary filed ? why ?
is it because when we pull by keywe will get value ?
or any other reason also ?

The the multi field primary key needs to be treated as one unit.

The other fields do not.

Q2:
how this primary Key class is used in the Entiyty bean ?

Among other places in findByPrimaryKey method.

Q3:
can we make 2 Key class ? can we use these 2 in the Entity Bean ?

No only one.

Q4: i have a column say ALPHA and has the values say A,B,C etc in 3
rows respectively.

how do i make a Key class for such column type carrying these values ?

You can either use java.lang.String as your key class or
you can make 1 class which contains 1 field.

Arne