Check duplicate data entry in multi record block,which is a mandatory field

Question

Dear all,
I have a situation where i have to check duplicate data entry(on a particular field,which is a mandatory field,i.e. it cannot be skipped by user without entering value) while data key-in in a Multi Record block.
As for reference I have used a logic,such as
1>In a When-Validate-Record trigger of that block I am assigning the value of that current item in Table type variable(collection type)
as this trigger fire every time as soon as i leave that record,so its assigning the value of that current time.And this process continues
then
2>In a When-Validate-Item trigger of that corresponding item(i.e. the trigger is at item level) has been written,where it compares the value of that current item and the value stored in Table type variable(collection type) of When-Validate-Record trigger.If the current item value is matched with any value stored in Table type variable I am showing a message of ('Duplicate Record') following by raise_form_trigger failure
This code is working fine for checking duplicate value of that multi record field
The problem is that,if user enter the value in that field,and then goes to next field,enter value to that field and then press 'Enter Query 'icon,the bolth Validate trigger fires.As result first when-validate record fires,which stores that value,and then when-validate-item fires,as a result it shows duplicate record message
Please give me a meaningful logic or code for solving this problem
Any other logic to solve this problem is also welcome

Answer 1

@Ammad Ahmed
first of all thanks .your logic worked,but still i have some little bit of problem,
now the requirement is a master detail form where both master and detail is multirecord ,where detail cannot have duplicate record,
such as..........
MASTER:--
A code
A1
A2
DETAIL:--
D code
d1
d2 <-valid as for master A1 , detail d1 ,d2 are not duplicate
d2 <--invalid as as for master A1 , detail d2 ,d2 are duplicate
validation rule:  A Code –D Code combination is unique. The system will stop users from entering duplicate D Code for a A Code. Appropriate error message will be displayed.*
actually i am facing a typical problem,the same logic i have been applied in detail section ,its working fine when i am inserting new records.problem starts when i query,after query in ' a ' field say 2 records (i.e. which has been earlier saved) has been pasted,now if i insert a new record with the value exactly same with the already present value in the screen(i.e. value populated after query) its not showing duplicate.................could u tell me the reason?and help me out...............its urgent plzzzzzzzzz
Edited by: sushovan on Nov 22, 2010 4:34 AM
Edited by: sushovan on Nov 22, 2010 4:36 AM
Edited by: sushovan on Nov 22, 2010 8:58 AM