How to set values to a Odata Model for Read/Update

Hi
I need to set values to a Odata service before I call the READ operation. How do I set the values/properties

odata url - http://server:port/path/Entity(var1='v1',var2='v2',var3='v3')

How do I set the values for variables Var 1, var 2 & 3 programmatically

var oModel = new sap.ui.model.odata.ODataModel(ServiceURL);

Any help is helpful.

Regards
Aakash