自己的切片上的dynamoDB FilterExpression

I working on easy access to dynamoDB and I can't find out how to get object according to some props in own slice. What I need is a right expression.

I have this model:

type aaa struct {   
    Aa string         `json:"aaa"`
    Ac []bbb          `json:"aac"`
}

type bbb struct {   
    Ba string   `json:"bba"`
}

with this data

    a := &aaa{
    Aa: "Aa",
    Ac: []bbb{
        {
            Ba: "foo1",
        },
    },
}

for me is working expression like this

expression.Name("aac[0].bba").Equal(expression.Value("foo1"))

but i dont know index. So I was trying

expression.Name("aac.bba").Equal(expression.Value("foo1"))

but this is not working. I also trying contain

expression.Name("aac.bba").Contains("foo1")

but this was working only on scalar types. Any Idea how get the object if i don't know index? Thanks