Mismatched len of columns when inserting empty map into JSON column

[leodido]

Describe the bug

Steps to reproduce

1. Enable the experimental JSON type (eg., SET allow_experimental_object_type = 1)
2. Give to a column the experimental JSON type
3. Insert an empty map (ie., map[string]interface{}{})

Expected behavior

I'd expect the JSON column to accept empty maps like map[string]interface{}{}.

The same way it works if inputting a string representing an empty JSON (eg., "{}").

Instead, it results in an error (see below) coming from lib/proto/block.go.

Code example

To prove this bug I've modified your example clickhouse_api/json.go by adding a fourth column (Col4) (code below).

package main

import (
	"context"
	"fmt"

	"github.com/ClickHouse/clickhouse-go/v2"
)

func InsertReadJSON() error {
	opts := &clickhouse.Options{
		Settings: clickhouse.Settings{
			"allow_experimental_object_type": 1,
		},
	}

	conn, err := clickhouse.Open(opts)
	if err != nil {
		return err
	}
	ctx := context.Background()

	conn.Exec(ctx, "DROP TABLE IF EXISTS example")

	if err = conn.Exec(ctx, `
		CREATE TABLE example (
				Col1 JSON,
				Col2 JSON,
				Col3 JSON,
				Col4 JSON
			)
			Engine Memory
		`); err != nil {
		return err
	}

	type User struct {
		Name     string `json:"name"`
		Age      uint8  `json:"age"`
		Password string `ch:"-"`
	}

	defer func() {
		conn.Exec(ctx, "DROP TABLE example")
	}()
	batch, err := conn.PrepareBatch(ctx, "INSERT INTO example")
	if err != nil {
		return err
	}
	// we can insert JSON as either a string, struct or map
	col1Data := `{"name": "Clicky McClickHouse", "age": 40, "password": "password"}`
	col2Data := User{
		Name:     "Clicky McClickHouse Snr",
		Age:      uint8(80),
		Password: "random",
	}
	col3Data := map[string]any{
		"name":     "Clicky McClickHouse Jnr",
		"age":      uint8(10),
		"password": "clicky",
	}
	col4Data := map[string]interface{}{} // Notice that `{}` works resulting in an output of `map[_dummy:0]`

	// both named and unnamed can be added with slices
	if err = batch.Append(col1Data, col2Data, col3Data, col4Data); err != nil {
		return err
	}

	if err = batch.Send(); err != nil {
		return err
	}
	// we can scan JSON into either a map or struct
	var (
		col1 map[string]any
		col2 map[string]any
		col3 User
		col4 map[string]any
	)
	// named tuples can be retrieved into a map or slices, unnamed just slices
	if err = conn.QueryRow(ctx, "SELECT * FROM example").Scan(&col1, &col2, &col3, &col4); err != nil {
		return err
	}
	fmt.Printf("row: col1=%v, col2=%v, col3=%v\n, col4=%v\n", col1, col2, col3, col4)

	return nil
}

func main() {
	if err := InsertReadJSON(); err != nil {
		fmt.Println(err)
	}
}

Error log

When running the code above you'll get:

clickhouse [Encode]:  mismatched len of columns - expected 1, received 0 for col Col4

Notice that using col4 = "{}" instead it works as expected - ie. outputting the following:

row: col1=map[age:40 name:Clicky McClickHouse password:password], col2=map[age:80 name:Clicky McClickHouse Snr], col3={Clicky McClickHouse Jnr 10 }
, col4=map[_dummy:0]

Configuration

Environment

• Client version: 23.9.1.1854 (official build)
• Language version: github.com/ClickHouse/clickhouse-go/v2 v2.14.2
• OS: 23.9.1 revision 54466
• Interface: ClickHouse API

ClickHouse server

• ClickHouse Server version: 23.9.1 revision 54466
• ClickHouse Server non-default settings, if any: NONE
• CREATE TABLE statements for tables involved: NONE

[jkaflik]

Hi @leodido

Thanks for reporting this. I can confirm this issue exists:

package issues

import (
	"context"
	"github.com/ClickHouse/clickhouse-go/v2"
	clickhouse_tests "github.com/ClickHouse/clickhouse-go/v2/tests"
	"github.com/stretchr/testify/require"
	"testing"
)

func Test1113(t *testing.T) {
	var (
		conn, err = clickhouse_tests.GetConnection("issues", clickhouse.Settings{
			"max_execution_time":             60,
			"allow_experimental_object_type": true,
		}, nil, &clickhouse.Compression{
			Method: clickhouse.CompressionLZ4,
		})
	)
	ctx := context.Background()
	require.NoError(t, err)
	const ddl = `
		CREATE TABLE test_1113 (
			col_1 JSON,
			col_2 JSON
		) Engine MergeTree() ORDER BY tuple()
		`
	require.NoError(t, conn.Exec(ctx, ddl))
	defer func() {
		conn.Exec(ctx, "DROP TABLE IF EXISTS test_1113")
	}()

	batch, err := conn.PrepareBatch(context.Background(), "INSERT INTO test_1113")
	require.NoError(t, err)

	v1 := map[string]struct {
		Str string
	}{"a": {Str: "value"}}
	v2 := map[string]any{}

	require.NoError(t, batch.Append(v1, v2))
	require.NoError(t, batch.Send())
}