I have a multivalue field called category(which is also a store field) in which i need to add only distinct values

`<field name="category">value1</field>`  

`<field name="category">value2</field>`

If I do a update as follows  

`<add>`  

`<doc>`  

`<field name="id">E02</field>`  

`<field name="category" update="add">value2</field>`  

`</doc>`  

`</add>`  

I get the value2 stored twice   

`<field name="category">value1</field>`  

`<field name="category">value2</field>`  

`<field name="category">value2</field>`

I need to store/update only disctinct values in category fields which is a multivalue fields. How to do this solr?

Thanks in advance,
Jagadesh.