jackc/pgx · error

While scanning type information

Error message

While scanning type information: %w

What it means

Conn.LoadTypes could not scan a row of catalog metadata into the derivedTypeInfo struct — the result columns did not match the expected scan targets, or a value could not be converted.

Solutions

1. Unwrap to see the exact scan mismatch
2. Verify the PostgreSQL server version is supported by the generated catalog SQL
3. Check for an incompatible or misbehaving server (e.g. a proxy altering result shapes)

When it happens

Trigger: Thrown at derived_types.go:189 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jackc/pgx@ec1a0befd2 (2026-08-04). Data as JSON: /api/errors/83e754047e41d8b1. Report an issue: GitHub.

Appendix: source

Thrown at derived_types.go:189

	if len(typeNames) == 0 {
		return nil, fmt.Errorf("No type names were supplied.")
	}

	// Disregard server version errors. This will result in
	// the SQL not support recent structures such as multirange
	serverVersion, _ := serverVersion(c)
	sql := buildLoadDerivedTypesSQL(serverVersion, typeNames)
	rows, err := c.Query(ctx, sql, QueryResultFormats{TextFormatCode}, typeNames)
	if err != nil {
		return nil, fmt.Errorf("While generating load types query: %w", err)
	}
	defer rows.Close()
	result := make([]*pgtype.Type, 0, 100)
	for rows.Next() {
		ti := derivedTypeInfo{}
		err = rows.Scan(&ti.TypeName, &ti.NspName, &ti.Typtype, &ti.Typbasetype, &ti.Typelem, &ti.Oid, &ti.Rngtypid, &ti.Rngsubtype, &ti.Attnames, &ti.Atttypids)
		if err != nil {
			return nil, fmt.Errorf("While scanning type information: %w", err)
		}
		var type_ *pgtype.Type
		switch ti.Typtype {
		case "b": // array
			dt, ok := m.TypeForOID(ti.Typelem)
			if !ok {
				return nil, fmt.Errorf("Array element OID %v not registered while loading pgtype %q", ti.Typelem, ti.TypeName)
			}
			type_ = &pgtype.Type{Name: ti.TypeName, OID: ti.Oid, Codec: &pgtype.ArrayCodec{ElementType: dt}}
		case "c": // composite
			var fields []pgtype.CompositeCodecField
			for i, fieldName := range ti.Attnames {
				dt, ok := m.TypeForOID(ti.Atttypids[i])
				if !ok {
					return nil, fmt.Errorf("Unknown field for composite type %q:  field %q (OID %v) is not already registered.", ti.TypeName, fieldName, ti.Atttypids[i])
				}
				fields = append(fields, pgtype.CompositeCodecField{Name: fieldName, Type: dt})
			}

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