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rows.go
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rows.go
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package pgx
import (
"context"
"errors"
"fmt"
"reflect"
"strings"
"sync"
"time"
"github.com/jackc/pgx/v5/pgconn"
"github.com/jackc/pgx/v5/pgtype"
)
// Rows is the result set returned from *Conn.Query. Rows must be closed before
// the *Conn can be used again. Rows are closed by explicitly calling Close(),
// calling Next() until it returns false, or when a fatal error occurs.
//
// Once a Rows is closed the only methods that may be called are Close(), Err(),
// and CommandTag().
//
// Rows is an interface instead of a struct to allow tests to mock Query. However,
// adding a method to an interface is technically a breaking change. Because of this
// the Rows interface is partially excluded from semantic version requirements.
// Methods will not be removed or changed, but new methods may be added.
type Rows interface {
// Close closes the rows, making the connection ready for use again. It is safe
// to call Close after rows is already closed.
Close()
// Err returns any error that occurred while reading. Err must only be called after the Rows is closed (either by
// calling Close or by Next returning false). If it is called early it may return nil even if there was an error
// executing the query.
Err() error
// CommandTag returns the command tag from this query. It is only available after Rows is closed.
CommandTag() pgconn.CommandTag
// FieldDescriptions returns the field descriptions of the columns. It may return nil. In particular this can occur
// when there was an error executing the query.
FieldDescriptions() []pgconn.FieldDescription
// Next prepares the next row for reading. It returns true if there is another
// row and false if no more rows are available or a fatal error has occurred.
// It automatically closes rows when all rows are read.
//
// Callers should check rows.Err() after rows.Next() returns false to detect
// whether result-set reading ended prematurely due to an error. See
// Conn.Query for details.
//
// For simpler error handling, consider using the higher-level pgx v5
// CollectRows() and ForEachRow() helpers instead.
Next() bool
// Scan reads the values from the current row into dest values positionally.
// dest can include pointers to core types, values implementing the Scanner
// interface, and nil. nil will skip the value entirely. It is an error to
// call Scan without first calling Next() and checking that it returned true.
Scan(dest ...any) error
// Values returns the decoded row values. As with Scan(), it is an error to
// call Values without first calling Next() and checking that it returned
// true.
Values() ([]any, error)
// RawValues returns the unparsed bytes of the row values. The returned data is only valid until the next Next
// call or the Rows is closed.
RawValues() [][]byte
// Conn returns the underlying *Conn on which the query was executed. This may return nil if Rows did not come from a
// *Conn (e.g. if it was created by RowsFromResultReader)
Conn() *Conn
}
// Row is a convenience wrapper over Rows that is returned by QueryRow.
//
// Row is an interface instead of a struct to allow tests to mock QueryRow. However,
// adding a method to an interface is technically a breaking change. Because of this
// the Row interface is partially excluded from semantic version requirements.
// Methods will not be removed or changed, but new methods may be added.
type Row interface {
// Scan works the same as Rows. with the following exceptions. If no
// rows were found it returns ErrNoRows. If multiple rows are returned it
// ignores all but the first.
Scan(dest ...any) error
}
// RowScanner scans an entire row at a time into the RowScanner.
type RowScanner interface {
// ScanRows scans the row.
ScanRow(rows Rows) error
}
// connRow implements the Row interface for Conn.QueryRow.
type connRow baseRows
func (r *connRow) Scan(dest ...any) (err error) {
rows := (*baseRows)(r)
if rows.Err() != nil {
return rows.Err()
}
for _, d := range dest {
if _, ok := d.(*pgtype.DriverBytes); ok {
rows.Close()
return fmt.Errorf("cannot scan into *pgtype.DriverBytes from QueryRow")
}
}
if !rows.Next() {
if rows.Err() == nil {
return ErrNoRows
}
return rows.Err()
}
rows.Scan(dest...)
rows.Close()
return rows.Err()
}
// baseRows implements the Rows interface for Conn.Query.
type baseRows struct {
typeMap *pgtype.Map
resultReader *pgconn.ResultReader
values [][]byte
commandTag pgconn.CommandTag
err error
closed bool
scanPlans []pgtype.ScanPlan
scanTypes []reflect.Type
conn *Conn
multiResultReader *pgconn.MultiResultReader
queryTracer QueryTracer
batchTracer BatchTracer
ctx context.Context
startTime time.Time
sql string
args []any
rowCount int
}
func (rows *baseRows) FieldDescriptions() []pgconn.FieldDescription {
return rows.resultReader.FieldDescriptions()
}
func (rows *baseRows) Close() {
if rows.closed {
return
}
rows.closed = true
if rows.resultReader != nil {
var closeErr error
rows.commandTag, closeErr = rows.resultReader.Close()
if rows.err == nil {
rows.err = closeErr
}
}
if rows.multiResultReader != nil {
closeErr := rows.multiResultReader.Close()
if rows.err == nil {
rows.err = closeErr
}
}
if rows.err != nil && rows.conn != nil && rows.sql != "" {
if sc := rows.conn.statementCache; sc != nil {
sc.Invalidate(rows.sql)
}
if sc := rows.conn.descriptionCache; sc != nil {
sc.Invalidate(rows.sql)
}
}
if rows.batchTracer != nil {
rows.batchTracer.TraceBatchQuery(rows.ctx, rows.conn, TraceBatchQueryData{SQL: rows.sql, Args: rows.args, CommandTag: rows.commandTag, Err: rows.err})
} else if rows.queryTracer != nil {
rows.queryTracer.TraceQueryEnd(rows.ctx, rows.conn, TraceQueryEndData{rows.commandTag, rows.err})
}
}
func (rows *baseRows) CommandTag() pgconn.CommandTag {
return rows.commandTag
}
func (rows *baseRows) Err() error {
return rows.err
}
// fatal signals an error occurred after the query was sent to the server. It
// closes the rows automatically.
func (rows *baseRows) fatal(err error) {
if rows.err != nil {
return
}
rows.err = err
rows.Close()
}
func (rows *baseRows) Next() bool {
if rows.closed {
return false
}
if rows.resultReader.NextRow() {
rows.rowCount++
rows.values = rows.resultReader.Values()
return true
} else {
rows.Close()
return false
}
}
func (rows *baseRows) Scan(dest ...any) error {
m := rows.typeMap
fieldDescriptions := rows.FieldDescriptions()
values := rows.values
if len(fieldDescriptions) != len(values) {
err := fmt.Errorf("number of field descriptions must equal number of values, got %d and %d", len(fieldDescriptions), len(values))
rows.fatal(err)
return err
}
if len(dest) == 1 {
if rc, ok := dest[0].(RowScanner); ok {
err := rc.ScanRow(rows)
if err != nil {
rows.fatal(err)
}
return err
}
}
if len(fieldDescriptions) != len(dest) {
err := fmt.Errorf("number of field descriptions must equal number of destinations, got %d and %d", len(fieldDescriptions), len(dest))
rows.fatal(err)
return err
}
if rows.scanPlans == nil {
rows.scanPlans = make([]pgtype.ScanPlan, len(values))
rows.scanTypes = make([]reflect.Type, len(values))
for i := range dest {
rows.scanPlans[i] = m.PlanScan(fieldDescriptions[i].DataTypeOID, fieldDescriptions[i].Format, dest[i])
rows.scanTypes[i] = reflect.TypeOf(dest[i])
}
}
for i, dst := range dest {
if dst == nil {
continue
}
if rows.scanTypes[i] != reflect.TypeOf(dst) {
rows.scanPlans[i] = m.PlanScan(fieldDescriptions[i].DataTypeOID, fieldDescriptions[i].Format, dest[i])
rows.scanTypes[i] = reflect.TypeOf(dest[i])
}
err := rows.scanPlans[i].Scan(values[i], dst)
if err != nil {
err = ScanArgError{ColumnIndex: i, Err: err}
rows.fatal(err)
return err
}
}
return nil
}
func (rows *baseRows) Values() ([]any, error) {
if rows.closed {
return nil, errors.New("rows is closed")
}
values := make([]any, 0, len(rows.FieldDescriptions()))
for i := range rows.FieldDescriptions() {
buf := rows.values[i]
fd := &rows.FieldDescriptions()[i]
if buf == nil {
values = append(values, nil)
continue
}
if dt, ok := rows.typeMap.TypeForOID(fd.DataTypeOID); ok {
value, err := dt.Codec.DecodeValue(rows.typeMap, fd.DataTypeOID, fd.Format, buf)
if err != nil {
rows.fatal(err)
}
values = append(values, value)
} else {
switch fd.Format {
case TextFormatCode:
values = append(values, string(buf))
case BinaryFormatCode:
newBuf := make([]byte, len(buf))
copy(newBuf, buf)
values = append(values, newBuf)
default:
rows.fatal(errors.New("unknown format code"))
}
}
if rows.Err() != nil {
return nil, rows.Err()
}
}
return values, rows.Err()
}
func (rows *baseRows) RawValues() [][]byte {
return rows.values
}
func (rows *baseRows) Conn() *Conn {
return rows.conn
}
type ScanArgError struct {
ColumnIndex int
Err error
}
func (e ScanArgError) Error() string {
return fmt.Sprintf("can't scan into dest[%d]: %v", e.ColumnIndex, e.Err)
}
func (e ScanArgError) Unwrap() error {
return e.Err
}
// ScanRow decodes raw row data into dest. It can be used to scan rows read from the lower level pgconn interface.
//
// typeMap - OID to Go type mapping.
// fieldDescriptions - OID and format of values
// values - the raw data as returned from the PostgreSQL server
// dest - the destination that values will be decoded into
func ScanRow(typeMap *pgtype.Map, fieldDescriptions []pgconn.FieldDescription, values [][]byte, dest ...any) error {
if len(fieldDescriptions) != len(values) {
return fmt.Errorf("number of field descriptions must equal number of values, got %d and %d", len(fieldDescriptions), len(values))
}
if len(fieldDescriptions) != len(dest) {
return fmt.Errorf("number of field descriptions must equal number of destinations, got %d and %d", len(fieldDescriptions), len(dest))
}
for i, d := range dest {
if d == nil {
continue
}
err := typeMap.Scan(fieldDescriptions[i].DataTypeOID, fieldDescriptions[i].Format, values[i], d)
if err != nil {
return ScanArgError{ColumnIndex: i, Err: err}
}
}
return nil
}
// RowsFromResultReader returns a Rows that will read from values resultReader and decode with typeMap. It can be used
// to read from the lower level pgconn interface.
func RowsFromResultReader(typeMap *pgtype.Map, resultReader *pgconn.ResultReader) Rows {
return &baseRows{
typeMap: typeMap,
resultReader: resultReader,
}
}
// ForEachRow iterates through rows. For each row it scans into the elements of scans and calls fn. If any row
// fails to scan or fn returns an error the query will be aborted and the error will be returned. Rows will be closed
// when ForEachRow returns.
func ForEachRow(rows Rows, scans []any, fn func() error) (pgconn.CommandTag, error) {
defer rows.Close()
for rows.Next() {
err := rows.Scan(scans...)
if err != nil {
return pgconn.CommandTag{}, err
}
err = fn()
if err != nil {
return pgconn.CommandTag{}, err
}
}
if err := rows.Err(); err != nil {
return pgconn.CommandTag{}, err
}
return rows.CommandTag(), nil
}
// CollectableRow is the subset of Rows methods that a RowToFunc is allowed to call.
type CollectableRow interface {
FieldDescriptions() []pgconn.FieldDescription
Scan(dest ...any) error
Values() ([]any, error)
RawValues() [][]byte
}
// RowToFunc is a function that scans or otherwise converts row to a T.
type RowToFunc[T any] func(row CollectableRow) (T, error)
// AppendRows iterates through rows, calling fn for each row, and appending the results into a slice of T.
//
// This function closes the rows automatically on return.
func AppendRows[T any, S ~[]T](slice S, rows Rows, fn RowToFunc[T]) (S, error) {
defer rows.Close()
for rows.Next() {
value, err := fn(rows)
if err != nil {
return nil, err
}
slice = append(slice, value)
}
if err := rows.Err(); err != nil {
return nil, err
}
return slice, nil
}
// CollectRows iterates through rows, calling fn for each row, and collecting the results into a slice of T.
//
// This function closes the rows automatically on return.
func CollectRows[T any](rows Rows, fn RowToFunc[T]) ([]T, error) {
return AppendRows([]T{}, rows, fn)
}
// CollectOneRow calls fn for the first row in rows and returns the result. If no rows are found returns an error where errors.Is(ErrNoRows) is true.
// CollectOneRow is to CollectRows as QueryRow is to Query.
//
// This function closes the rows automatically on return.
func CollectOneRow[T any](rows Rows, fn RowToFunc[T]) (T, error) {
defer rows.Close()
var value T
var err error
if !rows.Next() {
if err = rows.Err(); err != nil {
return value, err
}
return value, ErrNoRows
}
value, err = fn(rows)
if err != nil {
return value, err
}
rows.Close()
return value, rows.Err()
}
// CollectExactlyOneRow calls fn for the first row in rows and returns the result.
// - If no rows are found returns an error where errors.Is(ErrNoRows) is true.
// - If more than 1 row is found returns an error where errors.Is(ErrTooManyRows) is true.
//
// This function closes the rows automatically on return.
func CollectExactlyOneRow[T any](rows Rows, fn RowToFunc[T]) (T, error) {
defer rows.Close()
var (
err error
value T
)
if !rows.Next() {
if err = rows.Err(); err != nil {
return value, err
}
return value, ErrNoRows
}
value, err = fn(rows)
if err != nil {
return value, err
}
if rows.Next() {
var zero T
return zero, ErrTooManyRows
}
return value, rows.Err()
}
// RowTo returns a T scanned from row.
func RowTo[T any](row CollectableRow) (T, error) {
var value T
err := row.Scan(&value)
return value, err
}
// RowTo returns a the address of a T scanned from row.
func RowToAddrOf[T any](row CollectableRow) (*T, error) {
var value T
err := row.Scan(&value)
return &value, err
}
// RowToMap returns a map scanned from row.
func RowToMap(row CollectableRow) (map[string]any, error) {
var value map[string]any
err := row.Scan((*mapRowScanner)(&value))
return value, err
}
type mapRowScanner map[string]any
func (rs *mapRowScanner) ScanRow(rows Rows) error {
values, err := rows.Values()
if err != nil {
return err
}
*rs = make(mapRowScanner, len(values))
for i := range values {
(*rs)[string(rows.FieldDescriptions()[i].Name)] = values[i]
}
return nil
}
// RowToStructByPos returns a T scanned from row. T must be a struct. T must have the same number a public fields as row
// has fields. The row and T fields will be matched by position. If the "db" struct tag is "-" then the field will be
// ignored.
func RowToStructByPos[T any](row CollectableRow) (T, error) {
var value T
err := (&positionalStructRowScanner{ptrToStruct: &value}).ScanRow(row)
return value, err
}
// RowToAddrOfStructByPos returns the address of a T scanned from row. T must be a struct. T must have the same number a
// public fields as row has fields. The row and T fields will be matched by position. If the "db" struct tag is "-" then
// the field will be ignored.
func RowToAddrOfStructByPos[T any](row CollectableRow) (*T, error) {
var value T
err := (&positionalStructRowScanner{ptrToStruct: &value}).ScanRow(row)
return &value, err
}
type positionalStructRowScanner struct {
ptrToStruct any
}
func (rs *positionalStructRowScanner) ScanRow(rows CollectableRow) error {
typ := reflect.TypeOf(rs.ptrToStruct).Elem()
fields := lookupStructFields(typ)
if len(rows.RawValues()) > len(fields) {
return fmt.Errorf(
"got %d values, but dst struct has only %d fields",
len(rows.RawValues()),
len(fields),
)
}
scanTargets := setupStructScanTargets(rs.ptrToStruct, fields)
return rows.Scan(scanTargets...)
}
// Map from reflect.Type -> []structRowField
var positionalStructFieldMap sync.Map
func lookupStructFields(t reflect.Type) []structRowField {
if cached, ok := positionalStructFieldMap.Load(t); ok {
return cached.([]structRowField)
}
fieldStack := make([]int, 0, 1)
fields := computeStructFields(t, make([]structRowField, 0, t.NumField()), &fieldStack)
fieldsIface, _ := positionalStructFieldMap.LoadOrStore(t, fields)
return fieldsIface.([]structRowField)
}
func computeStructFields(
t reflect.Type,
fields []structRowField,
fieldStack *[]int,
) []structRowField {
tail := len(*fieldStack)
*fieldStack = append(*fieldStack, 0)
for i := 0; i < t.NumField(); i++ {
sf := t.Field(i)
(*fieldStack)[tail] = i
// Handle anonymous struct embedding, but do not try to handle embedded pointers.
if sf.Anonymous && sf.Type.Kind() == reflect.Struct {
fields = computeStructFields(sf.Type, fields, fieldStack)
} else if sf.PkgPath == "" {
dbTag, _ := sf.Tag.Lookup(structTagKey)
if dbTag == "-" {
// Field is ignored, skip it.
continue
}
fields = append(fields, structRowField{
path: append([]int(nil), *fieldStack...),
})
}
}
*fieldStack = (*fieldStack)[:tail]
return fields
}
// RowToStructByName returns a T scanned from row. T must be a struct. T must have the same number of named public
// fields as row has fields. The row and T fields will be matched by name. The match is case-insensitive. The database
// column name can be overridden with a "db" struct tag. If the "db" struct tag is "-" then the field will be ignored.
func RowToStructByName[T any](row CollectableRow) (T, error) {
var value T
err := (&namedStructRowScanner{ptrToStruct: &value}).ScanRow(row)
return value, err
}
// RowToAddrOfStructByName returns the address of a T scanned from row. T must be a struct. T must have the same number
// of named public fields as row has fields. The row and T fields will be matched by name. The match is
// case-insensitive. The database column name can be overridden with a "db" struct tag. If the "db" struct tag is "-"
// then the field will be ignored.
func RowToAddrOfStructByName[T any](row CollectableRow) (*T, error) {
var value T
err := (&namedStructRowScanner{ptrToStruct: &value}).ScanRow(row)
return &value, err
}
// RowToStructByNameLax returns a T scanned from row. T must be a struct. T must have greater than or equal number of named public
// fields as row has fields. The row and T fields will be matched by name. The match is case-insensitive. The database
// column name can be overridden with a "db" struct tag. If the "db" struct tag is "-" then the field will be ignored.
func RowToStructByNameLax[T any](row CollectableRow) (T, error) {
var value T
err := (&namedStructRowScanner{ptrToStruct: &value, lax: true}).ScanRow(row)
return value, err
}
// RowToAddrOfStructByNameLax returns the address of a T scanned from row. T must be a struct. T must have greater than or
// equal number of named public fields as row has fields. The row and T fields will be matched by name. The match is
// case-insensitive. The database column name can be overridden with a "db" struct tag. If the "db" struct tag is "-"
// then the field will be ignored.
func RowToAddrOfStructByNameLax[T any](row CollectableRow) (*T, error) {
var value T
err := (&namedStructRowScanner{ptrToStruct: &value, lax: true}).ScanRow(row)
return &value, err
}
type namedStructRowScanner struct {
ptrToStruct any
lax bool
}
func (rs *namedStructRowScanner) ScanRow(rows CollectableRow) error {
typ := reflect.TypeOf(rs.ptrToStruct).Elem()
fldDescs := rows.FieldDescriptions()
namedStructFields, err := lookupNamedStructFields(typ, fldDescs)
if err != nil {
return err
}
if !rs.lax && namedStructFields.missingField != "" {
return fmt.Errorf("cannot find field %s in returned row", namedStructFields.missingField)
}
fields := namedStructFields.fields
scanTargets := setupStructScanTargets(rs.ptrToStruct, fields)
return rows.Scan(scanTargets...)
}
// Map from namedStructFieldMap -> *namedStructFields
var namedStructFieldMap sync.Map
type namedStructFieldsKey struct {
t reflect.Type
colNames string
}
type namedStructFields struct {
fields []structRowField
// missingField is the first field from the struct without a corresponding row field.
// This is used to construct the correct error message for non-lax queries.
missingField string
}
func lookupNamedStructFields(
t reflect.Type,
fldDescs []pgconn.FieldDescription,
) (*namedStructFields, error) {
key := namedStructFieldsKey{
t: t,
colNames: joinFieldNames(fldDescs),
}
if cached, ok := namedStructFieldMap.Load(key); ok {
return cached.(*namedStructFields), nil
}
// We could probably do two-levels of caching, where we compute the key -> fields mapping
// for a type only once, cache it by type, then use that to compute the column -> fields
// mapping for a given set of columns.
fieldStack := make([]int, 0, 1)
fields, missingField := computeNamedStructFields(
fldDescs,
t,
make([]structRowField, len(fldDescs)),
&fieldStack,
)
for i, f := range fields {
if f.path == nil {
return nil, fmt.Errorf(
"struct doesn't have corresponding row field %s",
fldDescs[i].Name,
)
}
}
fieldsIface, _ := namedStructFieldMap.LoadOrStore(
key,
&namedStructFields{fields: fields, missingField: missingField},
)
return fieldsIface.(*namedStructFields), nil
}
func joinFieldNames(fldDescs []pgconn.FieldDescription) string {
switch len(fldDescs) {
case 0:
return ""
case 1:
return fldDescs[0].Name
}
totalSize := len(fldDescs) - 1 // Space for separator bytes.
for _, d := range fldDescs {
totalSize += len(d.Name)
}
var b strings.Builder
b.Grow(totalSize)
b.WriteString(fldDescs[0].Name)
for _, d := range fldDescs[1:] {
b.WriteByte(0) // Join with NUL byte as it's (presumably) not a valid column character.
b.WriteString(d.Name)
}
return b.String()
}
func computeNamedStructFields(
fldDescs []pgconn.FieldDescription,
t reflect.Type,
fields []structRowField,
fieldStack *[]int,
) ([]structRowField, string) {
var missingField string
tail := len(*fieldStack)
*fieldStack = append(*fieldStack, 0)
for i := 0; i < t.NumField(); i++ {
sf := t.Field(i)
(*fieldStack)[tail] = i
if sf.PkgPath != "" && !sf.Anonymous {
// Field is unexported, skip it.
continue
}
// Handle anonymous struct embedding, but do not try to handle embedded pointers.
if sf.Anonymous && sf.Type.Kind() == reflect.Struct {
var missingSubField string
fields, missingSubField = computeNamedStructFields(
fldDescs,
sf.Type,
fields,
fieldStack,
)
if missingField == "" {
missingField = missingSubField
}
} else {
dbTag, dbTagPresent := sf.Tag.Lookup(structTagKey)
if dbTagPresent {
dbTag, _, _ = strings.Cut(dbTag, ",")
}
if dbTag == "-" {
// Field is ignored, skip it.
continue
}
colName := dbTag
if !dbTagPresent {
colName = sf.Name
}
fpos := fieldPosByName(fldDescs, colName)
if fpos == -1 {
if missingField == "" {
missingField = colName
}
continue
}
fields[fpos] = structRowField{
path: append([]int(nil), *fieldStack...),
}
}
}
*fieldStack = (*fieldStack)[:tail]
return fields, missingField
}
const structTagKey = "db"
func fieldPosByName(fldDescs []pgconn.FieldDescription, field string) (i int) {
i = -1
for i, desc := range fldDescs {
// Snake case support.
field = strings.ReplaceAll(field, "_", "")
descName := strings.ReplaceAll(desc.Name, "_", "")
if strings.EqualFold(descName, field) {
return i
}
}
return
}
// structRowField describes a field of a struct.
//
// TODO: It would be a bit more efficient to track the path using the pointer
// offset within the (outermost) struct and use unsafe.Pointer arithmetic to
// construct references when scanning rows. However, it's not clear it's worth
// using unsafe for this.
type structRowField struct {
path []int
}
func setupStructScanTargets(receiver any, fields []structRowField) []any {
scanTargets := make([]any, len(fields))
v := reflect.ValueOf(receiver).Elem()
for i, f := range fields {
scanTargets[i] = v.FieldByIndex(f.path).Addr().Interface()
}
return scanTargets
}