Add <Cmp>TupleNamed for two-sided range-queries on tuples

[Drahflow]

I found no other way to

sometable.SelectBuilder(colSomeCol).
    Where(qb.GtOrEqTupleNamed(colCreatedAtID, 2, "start")).
    Where(qb.LtTupleNamed(colCreatedAtID, 2, "end")).

i.e. do specify a range scan on a tuple column with both ends of the range given. With only qb.GtOrEqTuple and qb.LtTuple the autogenerated names are both derived from the column name and collide, thus it is not possible to specify different ends for the range.

Before merging this, please also consider that tuple-element syntax has some conflict with gocql, which produces "col[0]" in SliceMap, and not "col_0" as gocqlx wants it during tuple binding.

Some options I see:

• Rename this PR's functions (or add yet more) with <Cmp>TupleIdx resp. <Cmp>TupleIdxNamed which autogenerate gocql compatible column names.
• Accept API breakage :( and change tupleparam.
• Introduce <Cmp>TupleNamedElements(column string, names ...string) which gives names for all elements (thereby also specifying count)

If you tell me which of these two options you'd like to see, I'll be preparing an according follow-up PR.

[mmatczuk]

For the sake of completeness its fine to add the named variants to tuple compare functions - please add test cases.

The maximal benefit in this area would come from a dedicated API that would allow to operate on tuple filed level see example code below.

type TupleCmp struct {
	column string
	lit   []lit
	param []param
}

func (t *TupleCmp) IdxParam(...) *TupleCmp {
}

func (t *TupleCmp) IdxParamNamed(...) *TupleCmp {
}

func (t *TupleCmp) IdxLit(...) *TupleCmp {
}

func (t *TupleCmp) Eq() Cmp {
	
}
...

func Tuple(column string) *TupleCmp {
	return &TupleCmp{
		column: column,
		lit:   make([]lit, 4),
		param: make([]param, 4),
	}
}

As for

Before merging this, please also consider that tuple-element syntax has some conflict with gocql, which produces "col[0]" in SliceMap, and not "col_0" as gocqlx wants it during tuple binding.

I think that it's not possible to bind a slice to a tuple, but maybe you can prove me wrong.

[Drahflow]

I think that it's not possible to bind a slice to a tuple, but maybe you can prove me wrong.

No idea about that, but I was referring to
https://github.com/gocql/gocql/blob/558dfae50b5d369de77dae132dbfa64968e3abd4/helpers.go#L290

... which produces entries like tuple_col[0] in the results fetched from cassandra.

So as of now (with or without this PR), input syntax for tuple elements is

q := c.Session.Query(
   tbl.SelectBuilder().
     Where(qb.eqTuple("tuple_col", 2)).
     ToCql(),
).BindMap(qb.M{
  "tuple_col_0": someValue,
  "tuple_col_1": someOtherValue,
})

but output syntax is

data := q.Iter().SliceMap()
for _, row := range data {
    fmt.Printf("%v %v\n",
      row["tuple_col[0]"],
      row["tuple_col[1]"],
    )
}

And that's quite an inconsistency.

[mmatczuk]

I guess we can fix that.

[mmatczuk]

Thanks!