I have some simple code to check if data exist in entity, when I save new data with isoverdue = true and data exists, it will show alert that data exists.
private string _entityname = "tss_rating";
QueryExpression Query = new QueryExpression(_entityname);  
Query.ColumnSet = new ColumnSet(true);
Query.Criteria.AddCondition("tss_isoverdue", ConditionOperator.Equal, true);
EntityCollection Items = organizationService.RetrieveMultiple(Query);
if (Items.Entities.Count > 0)
{
    Entity entity = new Entity(_entityname);
    if (entity.Contains("tss_isoverdue") && entity.Attributes["tss_isoverdue"].Equals(true))   // this if condition cannot be fire when input data
    {
        throw new Exception("IsOverdue with Yes Value is Exist....cannot create same data...!");
    }
}
Need suggestions.
UPDATE CODE AND IT WORKED:
public void Form_OnCreate_PreOperation(IOrganizationService organizationService, IPluginExecutionContext pluginExceptionContext, Entity CurrentEntity)
        {
            try
            {
                QueryExpression Query = new QueryExpression(pluginExceptionContext.PrimaryEntityName);  
                Query.ColumnSet = new ColumnSet(true);
                Query.Criteria.AddCondition("tss_isoverdue", ConditionOperator.Equal, true);
                EntityCollection Items = organizationService.RetrieveMultiple(Query);
                if (Items.Entities.Count > 0)
                {
                    if (CurrentEntity.Contains("tss_isoverdue"))
                    {
                        if ((bool)CurrentEntity.Attributes["tss_isoverdue"] == true)
                            throw new Exception("IsOverdue with Yes Value is Exist....cannot create same data...!");
                    }
                }
            }
            catch (Exception ex)
            {
                throw new InvalidPluginExecutionException(_classname + ".Form_OnCreate_PreOperation: " + ex.Message.ToString());
            }
        }
 
    