像给定示例一样，通过字段名称更新mongo事务

I am using labix as driver and I want to make transactions over couple collections, I found link http://blog.labix.org/2012/08/22/multi-doc-transactions-for-mongodb and I want to update in collection Owner and Employer not by Id but by Name field in collection. How can I achieve this ( simple switching Id with Name does not work ).

runner := txn.NewRunner(tcollection)
ops := []txn.Op{{
        C:      "accounts", 
        Id:     "aram",//Name
        Assert: M{"balance": M{"$gte": 100}},
        Update: M{"$inc": M{"balance": -100}},
}, {
        C:      "accounts",
        Id:     "ben",//Name
        Assert: M{"valid": true},
        Update: M{"$inc": M{"balance": 100}},
}}
id := bson.NewObjectId() // Optional
err := runner.Run(ops, id, nil)

I don't believe this is possible using the Op method based on the documentation. I believe the reasoning behind disallowing this is that if you were to allow transactions based on a set field rather than by the mongo-assigned ID, there is a risk that changes can be made on the wrong document (what if someone else has the name Ben that you don't want to apply this change to?).

Since transactions like this in Mongo are usually done by 2-phase staging it makes sense to me that the limitation for this usage is that you have to make an array of transaction Ops based on IDs you find by running a separate query by the account names.