[runtime] Support set map value by key

[pingginp]

Follow on relops#39

• C*2 https://docs.datastax.com/en/cql/3.1/cql/cql_using/use_map_t.html
• C*3 https://docs.datastax.com/en/cql/3.3/cql/cql_using/useInsertMap.html

AppendSlice is the base point to follow

const (
	NoCollectionType CollectionType = iota
	ListType
	SetType
	MapType
)

func appendList(c *Context, col ListColumn, values interface{}) {
	b := ColumnBinding{Column: col, Value: values, Incremental: true, CollectionType: ListType, CollectionOperationType: Append}
	c.Bindings = append(c.Bindings, b)
}

func prependList(c *Context, col ListColumn, values interface{}) {
	b := ColumnBinding{Column: col, Value: values, Incremental: true, CollectionType: ListType, CollectionOperationType: Prepend}
	c.Bindings = append(c.Bindings, b)
}

func removeList(c *Context, col ListColumn, values interface{}) {
	b := ColumnBinding{Column: col, Value: values, Incremental: true, CollectionType: ListType, CollectionOperationType: RemoveByValue}
	c.Bindings = append(c.Bindings, b)
}

func renderUpdate(ctx *Context, buf *bytes.Buffer, counterTable bool) {
           // ....
              switch binding.CollectionType {
			case ListType:
				switch binding.CollectionOperationType {
				case Append:
					setFragments[i] = fmt.Sprintf("%s = %s + ?", col, col)
				case Prepend:
					setFragments[i] = fmt.Sprintf("%s = ? + %s", col, col)
				case RemoveByValue:
					setFragments[i] = fmt.Sprintf("%s = %s - ?", col, col)
				}
			default:
				setFragments[i] = fmt.Sprintf("%s = ?", col)
			}
}

[pingginp]

the main challenge is map requires a column name and two value, so we will have two ? in query instead of just one ...

Although AppendStringSlice has values, it used for binding as value, not in query, only col is used in query

func (c *Context) AppendStringSlice(col StringSliceColumn, values ...string) SetValueStep {
	appendList(c, col, values)
	return c
}

SetStringStringMapValue(col StringStringMapColumn, key string, value string) SetValueStep

setFragments[i] = fmt.Sprintf("%s [?] = ?", col)

[pingginp]

it seems multiple ? is already handled in binding due to WHERE fo IN (?,?,?)

func (c *Context) Prepare(s *gocql.Session) (*gocql.Query, error) {
	// The reason why this is so dynamic is because of WHERE foo IN (?,?,?) clauses
	// The factoring for an IN clause is bad, since we are storing an array into the value
	// and using reflection to dig it out again
	// This should be more strongly typed
placeHolders := make([]interface{}, 0)

	for _, cond := range c.Conditions {
		v := cond.Binding.Value

		switch reflect.TypeOf(v).Kind() {
		case reflect.Slice:
			{
				s := reflect.ValueOf(v)
				for i := 0; i < s.Len(); i++ {
					placeHolders = append(placeHolders, s.Index(i).Interface())
				}
			}
		case reflect.Array:
			{

				// Not really happy about having to special case UUIDs
				// but this works for now

				if val, ok := v.(gocql.UUID); ok {
					placeHolders = append(placeHolders, val.Bytes())
				} else {
					return nil, bindingErrorf("Cannot bind component: %+v (type: %s)", v, reflect.TypeOf(v))
				}
			}
		default:
			{
				placeHolders = append(placeHolders, &v)
			}
		}
	}
}

[pingginp]

summarize what need to be done in order to get this work (previous commit already works, need to tweak the test and clean up code)

Actually it's all just runtime ....

• in tmpl/columns.tmpl
  • in SetStepValue interface, add Set{{Type1}}{{Type2}}MapValue(col, key {{type1}}, value {{type2}}
  • in Context methods, add the impl method with same name and call setMap
• run make cqlc/columns.go to generate using column_generator.go
• add setMap and use []interface{}{key, value} as Value for binding, set type to MapType and op to SetByKey
• in renderUpdate, use %s[?] = ? where %s is from col

BuildStatement, flatten binding, (copy from Prepare), former is used by Exec (update & insert) and latter is used by Fetch (select)

• NOTE: we added new struct KeyValue to avoid flatten slice value that should be kept as slice
• in old code, they were using &v for placeholder, it's pointer to interface, I don't know why it didn't trigger error, because gocql traverse ptr until it's a value?