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fix(DBI-1096 - clickhouse destination connector): Honor nullability for destination_type overrides in normalize #4783

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pfcoperez merged 1 commit into from
Sep 10, 2026
+50 −1
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fix(DBI-1096 - clickhouse destination connector): Honor nullability for destination_type overrides in normalize #4783

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3 changes: 2 additions & 1 deletion flow/connectors/clickhouse/normalize.go
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Expand Up @@ -216,7 +216,8 @@ func (c *ClickHouseConnector) generateCreateTableSQLForNormalizedTable(
if err != nil {
return nil, fmt.Errorf("error while converting column type to ClickHouse type: %w", err)
}
} else if (tableSchema.NullableEnabled || columnNullableEnabled) && column.Nullable && !colType.IsArray() {
} else if (tableSchema.NullableEnabled || columnNullableEnabled) && column.Nullable && !colType.IsArray() &&

@dtunikov dtunikov Sep 10, 2026

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afaiu tableSchema.NullableEnabled is kind of a global flag whether we want to have nullable fields at the destination at all (regardless of source column nullability)
so, I think it should be tableSchema.NullableEnabled && columnNullableEnabled, no?
if tableSchema.NullableEnabled is false, it means that none of the destination columns can be nullable

@dtunikov dtunikov Sep 10, 2026

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ah
we have schema.NullableEnabled and column.NullableEnabled
seems like we can put false on the schema lvl and override on the column lvl..
so OR is correct here I guess

@pfcoperez pfcoperez Sep 10, 2026

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seems like we can put false on the schema lvl and override on the column lvl..

Exactly, at least this is how I interpret it.

!strings.HasPrefix(clickHouseType, "Nullable(") {
clickHouseType = fmt.Sprintf("Nullable(%s)", clickHouseType)
}

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5 changes: 5 additions & 0 deletions flow/connectors/clickhouse/normalize_query.go
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Expand Up @@ -168,6 +168,11 @@ func (t *NormalizeQueryGenerator) BuildQuery(ctx context.Context) (string, error
if err != nil {
return "", fmt.Errorf("error while converting column type to clickhouse type: %w", err)
}
} else if (schema.NullableEnabled || columnNullableEnabled) && column.Nullable && !colType.IsArray() &&
!strings.HasPrefix(clickHouseType, "Nullable(") {
// mirror the table DDL: a nullable-enabled column created as Nullable(...) must also be

@dtunikov dtunikov Sep 10, 2026

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should we move it to the helper then?
if it's exactly the same condition as in flow/connectors/clickhouse/normalize.go.

@pfcoperez pfcoperez Sep 10, 2026

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It's the same condition today but JSON extraction function and DDL are different enough IMO as to maybe make us stumble upon different conditions in future changes.

// extracted as Nullable(...), or JSON nulls turn into the type's default value
clickHouseType = fmt.Sprintf("Nullable(%s)", clickHouseType)
}

switch clickHouseType {
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43 changes: 43 additions & 0 deletions flow/connectors/clickhouse/normalize_query_test.go
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Expand Up @@ -9,10 +9,53 @@ import (
"github.com/ClickHouse/clickhouse-go/v2"
"github.com/stretchr/testify/require"

"github.com/PeerDB-io/peerdb/flow/generated/protos"
"github.com/PeerDB-io/peerdb/flow/pkg/testutil"
"github.com/PeerDB-io/peerdb/flow/shared/types"
)

// TestBuildQueryNullableDestinationTypeOverride checks the normalize query agrees with the table DDL on
// nullability for `destination_type` overrides: with nullability enabled, the DDL creates the column as
// Nullable(<type>) so the query has to extract Nullable(<type>) too, or JSON nulls turn into the type's
// default value. An override already spelled Nullable(...) is used as is on both sides.
func TestBuildQueryNullableDestinationTypeOverride(t *testing.T) {
schema := &protos.TableSchema{
TableIdentifier: "src.t1",
PrimaryKeyColumns: []string{"id"},
System: protos.TypeSystem_Q,
NullableEnabled: true,
Columns: []*protos.FieldDescription{
{Name: "id", Type: string(types.QValueKindString), TypeModifier: -1},
{Name: "num", Type: string(types.QValueKindInt64), TypeModifier: -1, Nullable: true},
{Name: "tag", Type: string(types.QValueKindString), TypeModifier: -1, Nullable: true},
},
}
tableMapping := &protos.TableMapping{
SourceTableIdentifier: "src.t1",
DestinationTableIdentifier: "t1_dst",
Columns: []*protos.ColumnSetting{
{SourceName: "num", DestinationType: "Int64"},
{SourceName: "tag", DestinationType: "Nullable(String)"},
},
}

query, err := NewNormalizeQueryGenerator(
"t1_dst",
map[string]*protos.TableSchema{"t1_dst": schema},
[]*protos.TableMapping{tableMapping},
1, 0,
false, false,
nil, "_peerdb_raw_t1", nil, false, "", 0, nil,
).BuildQuery(t.Context())
require.NoError(t, err)

// nullable-enabled override extracts as Nullable, matching the Nullable(Int64) column the DDL creates
require.Contains(t, query, `JSONExtract(_peerdb_data, 'num', 'Nullable(Int64)') AS `+"`num`")
// an already-Nullable override is used verbatim, not double wrapped
require.Contains(t, query, `JSONExtract(_peerdb_data, 'tag', 'Nullable(String)') AS `+"`tag`")
require.NotContains(t, query, "Nullable(Nullable(")
}

func TestExtendedTimeToDateTime(t *testing.T) {
ctx := context.Background()
addr := fmt.Sprintf("%s:%d", testutil.ClickHouseTestHost(), testutil.ClickHouseTestPort())
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