fraenky8 / tables-to-go

import (

	"database/sql"

	"database/sql/driver"

	"errors"

	"fmt"

	"io/ioutil"

	"path/filepath"

	"reflect"

	"strings"

	"sync"

	"github.com/jmoiron/sqlx/reflectx"

)

// Although the NameMapper is convenient, in practice it should not

// be relied on except for application code.  If you are writing a library

// that uses sqlx, you should be aware that the name mappings you expect

// can be overridden by your user's application.

// NameMapper is used to map column names to struct field names.  By default,

// it uses strings.ToLower to lowercase struct field names.  It can be set

// to whatever you want, but it is encouraged to be set before sqlx is used

// as name-to-field mappings are cached after first use on a type.

var NameMapper = strings.ToLower

var origMapper = reflect.ValueOf(NameMapper)

// Rather than creating on init, this is created when necessary so that

// importers have time to customize the NameMapper.

var mpr *reflectx.Mapper

// mprMu protects mpr.

var mprMu sync.Mutex

// mapper returns a valid mapper using the configured NameMapper func.

func mapper() *reflectx.Mapper {

	mprMu.Lock()

	defer mprMu.Unlock()

	if mpr == nil {

		mpr = reflectx.NewMapperFunc("db", NameMapper)

	} else if origMapper != reflect.ValueOf(NameMapper) {

		// if NameMapper has changed, create a new mapper

		mpr = reflectx.NewMapperFunc("db", NameMapper)

		origMapper = reflect.ValueOf(NameMapper)

	}

	return mpr

}

// isScannable takes the reflect.Type and the actual dest value and returns

// whether or not it's Scannable.  Something is scannable if:

//   * it is not a struct

//   * it implements sql.Scanner

//   * it has no exported fields

func isScannable(t reflect.Type) bool {

	if reflect.PtrTo(t).Implements(_scannerInterface) {

		return true

	}

	if t.Kind() != reflect.Struct {

		return true

	}

	// it's not important that we use the right mapper for this particular object,

	// we're only concerned on how many exported fields this struct has

	m := mapper()

	if len(m.TypeMap(t).Index) == 0 {

		return true

	}

	return false

}

// ColScanner is an interface used by MapScan and SliceScan

type ColScanner interface {

	Columns() ([]string, error)

	Scan(dest ...interface{}) error

	Err() error

}

// Queryer is an interface used by Get and Select

type Queryer interface {

	Query(query string, args ...interface{}) (*sql.Rows, error)

	Queryx(query string, args ...interface{}) (*Rows, error)

	QueryRowx(query string, args ...interface{}) *Row

}

// Execer is an interface used by MustExec and LoadFile

type Execer interface {

	Exec(query string, args ...interface{}) (sql.Result, error)

}

// Binder is an interface for something which can bind queries (Tx, DB)

type binder interface {

	DriverName() string

	Rebind(string) string

	BindNamed(string, interface{}) (string, []interface{}, error)

}

// Ext is a union interface which can bind, query, and exec, used by

// NamedQuery and NamedExec.

type Ext interface {

	binder

	Queryer

	Execer

}

// Preparer is an interface used by Preparex.

type Preparer interface {

	Prepare(query string) (*sql.Stmt, error)

}

// determine if any of our extensions are unsafe

func isUnsafe(i interface{}) bool {

	switch v := i.(type) {

	case Row:

		return v.unsafe

	case *Row:

		return v.unsafe

	case Rows:

		return v.unsafe

	case *Rows:

		return v.unsafe

	case NamedStmt:

		return v.Stmt.unsafe

	case *NamedStmt:

		return v.Stmt.unsafe

	case Stmt:

		return v.unsafe

	case *Stmt:

		return v.unsafe

	case qStmt:

		return v.unsafe

	case *qStmt:

		return v.unsafe

	case DB:

		return v.unsafe

	case *DB:

		return v.unsafe

	case Tx:

		return v.unsafe

	case *Tx:

		return v.unsafe

	case sql.Rows, *sql.Rows:

		return false

	default:

		return false

	}

}

func mapperFor(i interface{}) *reflectx.Mapper {

	switch i.(type) {

	case DB:

		return i.(DB).Mapper

	case *DB:

		return i.(*DB).Mapper

	case Tx:

		return i.(Tx).Mapper

	case *Tx:

		return i.(*Tx).Mapper

	default:

		return mapper()

	}

}

var _scannerInterface = reflect.TypeOf((*sql.Scanner)(nil)).Elem()

var _valuerInterface = reflect.TypeOf((*driver.Valuer)(nil)).Elem()

// Row is a reimplementation of sql.Row in order to gain access to the underlying

// sql.Rows.Columns() data, necessary for StructScan.

type Row struct {

	err    error

	unsafe bool

	rows   *sql.Rows

	Mapper *reflectx.Mapper

}

// Scan is a fixed implementation of sql.Row.Scan, which does not discard the

// underlying error from the internal rows object if it exists.

func (r *Row) Scan(dest ...interface{}) error {

	if r.err != nil {

		return r.err

	}

	// TODO(bradfitz): for now we need to defensively clone all

	// []byte that the driver returned (not permitting

	// *RawBytes in Rows.Scan), since we're about to close

	// the Rows in our defer, when we return from this function.

	// the contract with the driver.Next(...) interface is that it

	// can return slices into read-only temporary memory that's

	// only valid until the next Scan/Close.  But the TODO is that

	// for a lot of drivers, this copy will be unnecessary.  We

	// should provide an optional interface for drivers to

	// implement to say, "don't worry, the []bytes that I return

	// from Next will not be modified again." (for instance, if

	// they were obtained from the network anyway) But for now we

	// don't care.

	defer r.rows.Close()

	for _, dp := range dest {

		if _, ok := dp.(*sql.RawBytes); ok {

			return errors.New("sql: RawBytes isn't allowed on Row.Scan")

		}

	}

	if !r.rows.Next() {

		if err := r.rows.Err(); err != nil {

			return err

		}

		return sql.ErrNoRows

	}

	err := r.rows.Scan(dest...)

	if err != nil {

		return err

	}

	// Make sure the query can be processed to completion with no errors.

	if err := r.rows.Close(); err != nil {

		return err

	}

	return nil

}

// Columns returns the underlying sql.Rows.Columns(), or the deferred error usually

// returned by Row.Scan()

func (r *Row) Columns() ([]string, error) {

	if r.err != nil {

		return []string{}, r.err

	}

	return r.rows.Columns()

}

// ColumnTypes returns the underlying sql.Rows.ColumnTypes(), or the deferred error

func (r *Row) ColumnTypes() ([]*sql.ColumnType, error) {

	if r.err != nil {

		return []*sql.ColumnType{}, r.err

	}

	return r.rows.ColumnTypes()

}

// Err returns the error encountered while scanning.

// DB is a wrapper around sql.DB which keeps track of the driverName upon Open,

// used mostly to automatically bind named queries using the right bindvars.

type DB struct {

	*sql.DB

	driverName string

	unsafe     bool

	Mapper     *reflectx.Mapper

}

// NewDb returns a new sqlx DB wrapper for a pre-existing *sql.DB.  The

// driverName of the original database is required for named query support.

func NewDb(db *sql.DB, driverName string) *DB {

	return &DB{DB: db, driverName: driverName, Mapper: mapper()}

}

// DriverName returns the driverName passed to the Open function for this DB.

func (db *DB) DriverName() string {

	return db.driverName

}

// Open is the same as sql.Open, but returns an *sqlx.DB instead.

func Open(driverName, dataSourceName string) (*DB, error) {

	db, err := sql.Open(driverName, dataSourceName)

	if err != nil {

		return nil, err

	}

	return &DB{DB: db, driverName: driverName, Mapper: mapper()}, err

}

// MustOpen is the same as sql.Open, but returns an *sqlx.DB instead and panics on error.

func MustOpen(driverName, dataSourceName string) *DB {

	db, err := Open(driverName, dataSourceName)

	if err != nil {

		panic(err)

	}

	return db

}

// MapperFunc sets a new mapper for this db using the default sqlx struct tag

// and the provided mapper function.

func (db *DB) MapperFunc(mf func(string) string) {

	db.Mapper = reflectx.NewMapperFunc("db", mf)

}

// Rebind transforms a query from QUESTION to the DB driver's bindvar type.

func (db *DB) Rebind(query string) string {

	return Rebind(BindType(db.driverName), query)

}

// Unsafe returns a version of DB which will silently succeed to scan when

// columns in the SQL result have no fields in the destination struct.

// sqlx.Stmt and sqlx.Tx which are created from this DB will inherit its

// safety behavior.

func (db *DB) Unsafe() *DB {

	return &DB{DB: db.DB, driverName: db.driverName, unsafe: true, Mapper: db.Mapper}

}

// BindNamed binds a query using the DB driver's bindvar type.

func (db *DB) BindNamed(query string, arg interface{}) (string, []interface{}, error) {

	return bindNamedMapper(BindType(db.driverName), query, arg, db.Mapper)

}

// NamedQuery using this DB.

// Any named placeholder parameters are replaced with fields from arg.

func (db *DB) NamedQuery(query string, arg interface{}) (*Rows, error) {

	return NamedQuery(db, query, arg)

}

// NamedExec using this DB.

// Any named placeholder parameters are replaced with fields from arg.

func (db *DB) NamedExec(query string, arg interface{}) (sql.Result, error) {

	return NamedExec(db, query, arg)

}

// Select using this DB.

// Any placeholder parameters are replaced with supplied args.

func (db *DB) Select(dest interface{}, query string, args ...interface{}) error {

	return Select(db, dest, query, args...)

}

// Get using this DB.

// Any placeholder parameters are replaced with supplied args.

// An error is returned if the result set is empty.

func (db *DB) Get(dest interface{}, query string, args ...interface{}) error {

	return Get(db, dest, query, args...)

}

// MustBegin starts a transaction, and panics on error.  Returns an *sqlx.Tx instead

// of an *sql.Tx.

func (db *DB) MustBegin() *Tx {

	tx, err := db.Beginx()

	if err != nil {

		panic(err)

	}

	return tx

}

// Beginx begins a transaction and returns an *sqlx.Tx instead of an *sql.Tx.

func (db *DB) Beginx() (*Tx, error) {

	tx, err := db.DB.Begin()

	if err != nil {

		return nil, err

	}

	return &Tx{Tx: tx, driverName: db.driverName, unsafe: db.unsafe, Mapper: db.Mapper}, err

}

// Queryx queries the database and returns an *sqlx.Rows.

// Any placeholder parameters are replaced with supplied args.

func (db *DB) Queryx(query string, args ...interface{}) (*Rows, error) {

	r, err := db.DB.Query(query, args...)

	if err != nil {

		return nil, err

	}

	return &Rows{Rows: r, unsafe: db.unsafe, Mapper: db.Mapper}, err

}

// QueryRowx queries the database and returns an *sqlx.Row.

// Any placeholder parameters are replaced with supplied args.

func (db *DB) QueryRowx(query string, args ...interface{}) *Row {

	rows, err := db.DB.Query(query, args...)

	return &Row{rows: rows, err: err, unsafe: db.unsafe, Mapper: db.Mapper}

}

// MustExec (panic) runs MustExec using this database.

// Any placeholder parameters are replaced with supplied args.

func (db *DB) MustExec(query string, args ...interface{}) sql.Result {

	return MustExec(db, query, args...)

}

// Preparex returns an sqlx.Stmt instead of a sql.Stmt

func (db *DB) Preparex(query string) (*Stmt, error) {

	return Preparex(db, query)

}

// PrepareNamed returns an sqlx.NamedStmt

func (db *DB) PrepareNamed(query string) (*NamedStmt, error) {

	return prepareNamed(db, query)

}

// Tx is an sqlx wrapper around sql.Tx with extra functionality

type Tx struct {

	*sql.Tx

	driverName string

	unsafe     bool

	Mapper     *reflectx.Mapper

}

// DriverName returns the driverName used by the DB which began this transaction.

func (tx *Tx) DriverName() string {

	return tx.driverName

}

// Rebind a query within a transaction's bindvar type.

func (tx *Tx) Rebind(query string) string {

	return Rebind(BindType(tx.driverName), query)

}

// Unsafe returns a version of Tx which will silently succeed to scan when

// columns in the SQL result have no fields in the destination struct.

func (tx *Tx) Unsafe() *Tx {

	return &Tx{Tx: tx.Tx, driverName: tx.driverName, unsafe: true, Mapper: tx.Mapper}

}

// BindNamed binds a query within a transaction's bindvar type.

func (tx *Tx) BindNamed(query string, arg interface{}) (string, []interface{}, error) {

	return bindNamedMapper(BindType(tx.driverName), query, arg, tx.Mapper)

}

// NamedQuery within a transaction.

// Any named placeholder parameters are replaced with fields from arg.

func (tx *Tx) NamedQuery(query string, arg interface{}) (*Rows, error) {

	return NamedQuery(tx, query, arg)

}

// NamedExec a named query within a transaction.

// Any named placeholder parameters are replaced with fields from arg.

func (tx *Tx) NamedExec(query string, arg interface{}) (sql.Result, error) {

	return NamedExec(tx, query, arg)

}

// Select within a transaction.

// Any placeholder parameters are replaced with supplied args.

func (tx *Tx) Select(dest interface{}, query string, args ...interface{}) error {

	return Select(tx, dest, query, args...)

}

// Queryx within a transaction.

// Any placeholder parameters are replaced with supplied args.

func (tx *Tx) Queryx(query string, args ...interface{}) (*Rows, error) {

	r, err := tx.Tx.Query(query, args...)

	if err != nil {

		return nil, err

	}

	return &Rows{Rows: r, unsafe: tx.unsafe, Mapper: tx.Mapper}, err

}

// QueryRowx within a transaction.

// Any placeholder parameters are replaced with supplied args.

func (tx *Tx) QueryRowx(query string, args ...interface{}) *Row {

	rows, err := tx.Tx.Query(query, args...)

	return &Row{rows: rows, err: err, unsafe: tx.unsafe, Mapper: tx.Mapper}

}

// Get within a transaction.

// Any placeholder parameters are replaced with supplied args.

// An error is returned if the result set is empty.

func (tx *Tx) Get(dest interface{}, query string, args ...interface{}) error {

	return Get(tx, dest, query, args...)

}

// MustExec runs MustExec within a transaction.

// Any placeholder parameters are replaced with supplied args.

func (tx *Tx) MustExec(query string, args ...interface{}) sql.Result {

	return MustExec(tx, query, args...)

}

// Preparex  a statement within a transaction.

func (tx *Tx) Preparex(query string) (*Stmt, error) {

	return Preparex(tx, query)

}

// Stmtx returns a version of the prepared statement which runs within a transaction.  Provided

// stmt can be either *sql.Stmt or *sqlx.Stmt.

func (tx *Tx) Stmtx(stmt interface{}) *Stmt {

	var s *sql.Stmt

	switch v := stmt.(type) {

	case Stmt:

		s = v.Stmt

	case *Stmt:

		s = v.Stmt

	case *sql.Stmt:

		s = v

	default:

		panic(fmt.Sprintf("non-statement type %v passed to Stmtx", reflect.ValueOf(stmt).Type()))

	}

	return &Stmt{Stmt: tx.Stmt(s), Mapper: tx.Mapper}

}

// NamedStmt returns a version of the prepared statement which runs within a transaction.

func (tx *Tx) NamedStmt(stmt *NamedStmt) *NamedStmt {

	return &NamedStmt{

		QueryString: stmt.QueryString,

		Params:      stmt.Params,

		Stmt:        tx.Stmtx(stmt.Stmt),

	}

}

// PrepareNamed returns an sqlx.NamedStmt

func (tx *Tx) PrepareNamed(query string) (*NamedStmt, error) {

	return prepareNamed(tx, query)

}

// Stmt is an sqlx wrapper around sql.Stmt with extra functionality

type Stmt struct {

	*sql.Stmt

	unsafe bool

	Mapper *reflectx.Mapper

}

// Unsafe returns a version of Stmt which will silently succeed to scan when

// columns in the SQL result have no fields in the destination struct.

func (s *Stmt) Unsafe() *Stmt {

	return &Stmt{Stmt: s.Stmt, unsafe: true, Mapper: s.Mapper}

}

// Select using the prepared statement.

// Any placeholder parameters are replaced with supplied args.

func (s *Stmt) Select(dest interface{}, args ...interface{}) error {

	return Select(&qStmt{s}, dest, "", args...)

}

// Get using the prepared statement.

// Any placeholder parameters are replaced with supplied args.

// An error is returned if the result set is empty.

func (s *Stmt) Get(dest interface{}, args ...interface{}) error {

	return Get(&qStmt{s}, dest, "", args...)

}

// MustExec (panic) using this statement.  Note that the query portion of the error

// output will be blank, as Stmt does not expose its query.

// Any placeholder parameters are replaced with supplied args.

func (s *Stmt) MustExec(args ...interface{}) sql.Result {

	return MustExec(&qStmt{s}, "", args...)

}

// QueryRowx using this statement.

// Any placeholder parameters are replaced with supplied args.

func (s *Stmt) QueryRowx(args ...interface{}) *Row {

	qs := &qStmt{s}

	return qs.QueryRowx("", args...)

}

// Queryx using this statement.

// Any placeholder parameters are replaced with supplied args.

func (s *Stmt) Queryx(args ...interface{}) (*Rows, error) {

	qs := &qStmt{s}

	return qs.Queryx("", args...)

}

// qStmt is an unexposed wrapper which lets you use a Stmt as a Queryer & Execer by

// implementing those interfaces and ignoring the `query` argument.

type qStmt struct{ *Stmt }

func (q *qStmt) Query(query string, args ...interface{}) (*sql.Rows, error) {

	return q.Stmt.Query(args...)

}

func (q *qStmt) Queryx(query string, args ...interface{}) (*Rows, error) {

	r, err := q.Stmt.Query(args...)

	if err != nil {

		return nil, err

	}

	return &Rows{Rows: r, unsafe: q.Stmt.unsafe, Mapper: q.Stmt.Mapper}, err

}

func (q *qStmt) QueryRowx(query string, args ...interface{}) *Row {

	rows, err := q.Stmt.Query(args...)

	return &Row{rows: rows, err: err, unsafe: q.Stmt.unsafe, Mapper: q.Stmt.Mapper}

}

func (q *qStmt) Exec(query string, args ...interface{}) (sql.Result, error) {

	return q.Stmt.Exec(args...)

}

// Rows is a wrapper around sql.Rows which caches costly reflect operations

// during a looped StructScan

type Rows struct {

	*sql.Rows

	unsafe bool

	Mapper *reflectx.Mapper

	// these fields cache memory use for a rows during iteration w/ structScan

	started bool

	fields  [][]int

	values  []interface{}

}

// SliceScan using this Rows.

func (r *Rows) SliceScan() ([]interface{}, error) {

	return SliceScan(r)

}

// MapScan using this Rows.

func (r *Rows) MapScan(dest map[string]interface{}) error {

	return MapScan(r, dest)

}

// StructScan is like sql.Rows.Scan, but scans a single Row into a single Struct.

// Use this and iterate over Rows manually when the memory load of Select() might be

// prohibitive.  *Rows.StructScan caches the reflect work of matching up column

// positions to fields to avoid that overhead per scan, which means it is not safe

// to run StructScan on the same Rows instance with different struct types.

func (r *Rows) StructScan(dest interface{}) error {

	v := reflect.ValueOf(dest)

	if v.Kind() != reflect.Ptr {

		return errors.New("must pass a pointer, not a value, to StructScan destination")

	}

	v = v.Elem()

	if !r.started {

		columns, err := r.Columns()

		if err != nil {

			return err

		}

		m := r.Mapper

		r.fields = m.TraversalsByName(v.Type(), columns)

		// if we are not unsafe and are missing fields, return an error

		if f, err := missingFields(r.fields); err != nil && !r.unsafe {

			return fmt.Errorf("missing destination name %s in %T", columns[f], dest)

		}

		r.values = make([]interface{}, len(columns))

		r.started = true

	}

	err := fieldsByTraversal(v, r.fields, r.values, true)

	if err != nil {

		return err

	}

	// scan into the struct field pointers and append to our results

	err = r.Scan(r.values...)

	if err != nil {

		return err

	}

	return r.Err()

}

// Connect to a database and verify with a ping.

func Connect(driverName, dataSourceName string) (*DB, error) {

	db, err := Open(driverName, dataSourceName)

	if err != nil {

		return nil, err

	}

	err = db.Ping()

	if err != nil {

		db.Close()

		return nil, err

	}

	return db, nil

}

// MustConnect connects to a database and panics on error.

func MustConnect(driverName, dataSourceName string) *DB {

	db, err := Connect(driverName, dataSourceName)

	if err != nil {

		panic(err)

	}

	return db

}

// Preparex prepares a statement.

func Preparex(p Preparer, query string) (*Stmt, error) {

	s, err := p.Prepare(query)

	if err != nil {

		return nil, err

	}

	return &Stmt{Stmt: s, unsafe: isUnsafe(p), Mapper: mapperFor(p)}, err

}

// Select executes a query using the provided Queryer, and StructScans each row

// into dest, which must be a slice.  If the slice elements are scannable, then

// the result set must have only one column.  Otherwise, StructScan is used.

// The *sql.Rows are closed automatically.

// Any placeholder parameters are replaced with supplied args.

func Select(q Queryer, dest interface{}, query string, args ...interface{}) error {

	rows, err := q.Queryx(query, args...)

	if err != nil {

		return err

	}

	// if something happens here, we want to make sure the rows are Closed

	defer rows.Close()

	return scanAll(rows, dest, false)

}

// Get does a QueryRow using the provided Queryer, and scans the resulting row

// to dest.  If dest is scannable, the result must only have one column.  Otherwise,

// StructScan is used.  Get will return sql.ErrNoRows like row.Scan would.

// Any placeholder parameters are replaced with supplied args.

// An error is returned if the result set is empty.

func Get(q Queryer, dest interface{}, query string, args ...interface{}) error {

	r := q.QueryRowx(query, args...)

	return r.scanAny(dest, false)

}

// LoadFile exec's every statement in a file (as a single call to Exec).

// LoadFile may return a nil *sql.Result if errors are encountered locating or

// reading the file at path.  LoadFile reads the entire file into memory, so it

// is not suitable for loading large data dumps, but can be useful for initializing

// schemas or loading indexes.

//

// FIXME: this does not really work with multi-statement files for mattn/go-sqlite3

// or the go-mysql-driver/mysql drivers;  pq seems to be an exception here.  Detecting

// this by requiring something with DriverName() and then attempting to split the

// queries will be difficult to get right, and its current driver-specific behavior

// is deemed at least not complex in its incorrectness.

func LoadFile(e Execer, path string) (*sql.Result, error) {

	realpath, err := filepath.Abs(path)

	if err != nil {

		return nil, err

	}

	contents, err := ioutil.ReadFile(realpath)

	if err != nil {

		return nil, err

	}

	res, err := e.Exec(string(contents))

	return &res, err

}

// MustExec execs the query using e and panics if there was an error.

// Any placeholder parameters are replaced with supplied args.

func MustExec(e Execer, query string, args ...interface{}) sql.Result {

	res, err := e.Exec(query, args...)

	if err != nil {

		panic(err)

	}

	return res

}

// SliceScan using this Rows.

func (r *Row) SliceScan() ([]interface{}, error) {

	return SliceScan(r)

}

// MapScan using this Rows.

func (r *Row) MapScan(dest map[string]interface{}) error {

	return MapScan(r, dest)

}

func (r *Row) scanAny(dest interface{}, structOnly bool) error {

	if r.err != nil {

		return r.err

	}

	if r.rows == nil {

		r.err = sql.ErrNoRows

		return r.err

	}

	defer r.rows.Close()

	v := reflect.ValueOf(dest)

	if v.Kind() != reflect.Ptr {

		return errors.New("must pass a pointer, not a value, to StructScan destination")

	}

	if v.IsNil() {

		return errors.New("nil pointer passed to StructScan destination")

	}

	base := reflectx.Deref(v.Type())

	scannable := isScannable(base)

	if structOnly && scannable {

		return structOnlyError(base)

	}

	columns, err := r.Columns()

	if err != nil {

		return err

	}

	if scannable && len(columns) > 1 {

		return fmt.Errorf("scannable dest type %s with >1 columns (%d) in result", base.Kind(), len(columns))

	}

	if scannable {

		return r.Scan(dest)

	}

	m := r.Mapper

	fields := m.TraversalsByName(v.Type(), columns)

	// if we are not unsafe and are missing fields, return an error

	if f, err := missingFields(fields); err != nil && !r.unsafe {

		return fmt.Errorf("missing destination name %s in %T", columns[f], dest)

	}

	values := make([]interface{}, len(columns))

	err = fieldsByTraversal(v, fields, values, true)

	if err != nil {

		return err

	}

	// scan into the struct field pointers and append to our results

	return r.Scan(values...)

}

// StructScan a single Row into dest.

func (r *Row) StructScan(dest interface{}) error {

	return r.scanAny(dest, true)

}

// SliceScan a row, returning a []interface{} with values similar to MapScan.

// This function is primarily intended for use where the number of columns

// is not known.  Because you can pass an []interface{} directly to Scan,

// it's recommended that you do that as it will not have to allocate new

// slices per row.

func SliceScan(r ColScanner) ([]interface{}, error) {

	// ignore r.started, since we needn't use reflect for anything.

	columns, err := r.Columns()

	if err != nil {

		return []interface{}{}, err

	}

	values := make([]interface{}, len(columns))

	for i := range values {

		values[i] = new(interface{})

	}

	err = r.Scan(values...)

	if err != nil {

		return values, err

	}

	for i := range columns {

		values[i] = *(values[i].(*interface{}))

	}

	return values, r.Err()

}

// MapScan scans a single Row into the dest map[string]interface{}.

// Use this to get results for SQL that might not be under your control

// (for instance, if you're building an interface for an SQL server that

// executes SQL from input).  Please do not use this as a primary interface!

// This will modify the map sent to it in place, so reuse the same map with

// care.  Columns which occur more than once in the result will overwrite

// each other!

func MapScan(r ColScanner, dest map[string]interface{}) error {

	// ignore r.started, since we needn't use reflect for anything.

	columns, err := r.Columns()

	if err != nil {

		return err

	}

	values := make([]interface{}, len(columns))

	for i := range values {

		values[i] = new(interface{})

	}

	err = r.Scan(values...)

	if err != nil {

		return err

	}

	for i, column := range columns {

		dest[column] = *(values[i].(*interface{}))

	}

	return r.Err()

}

type rowsi interface {

	Close() error

	Columns() ([]string, error)

	Err() error

	Next() bool

	Scan(...interface{}) error

}

// structOnlyError returns an error appropriate for type when a non-scannable

// struct is expected but something else is given

func structOnlyError(t reflect.Type) error {

	isStruct := t.Kind() == reflect.Struct

	isScanner := reflect.PtrTo(t).Implements(_scannerInterface)

	if !isStruct {

		return fmt.Errorf("expected %s but got %s", reflect.Struct, t.Kind())

	}

	if isScanner {

		return fmt.Errorf("structscan expects a struct dest but the provided struct type %s implements scanner", t.Name())

	}

	return fmt.Errorf("expected a struct, but struct %s has no exported fields", t.Name())

}

// scanAll scans all rows into a destination, which must be a slice of any

// type.  If the destination slice type is a Struct, then StructScan will be

// used on each row.  If the destination is some other kind of base type, then

// each row must only have one column which can scan into that type.  This

// allows you to do something like:

//

//    rows, _ := db.Query("select id from people;")

//    var ids []int

//    scanAll(rows, &ids, false)

//

// and ids will be a list of the id results.  I realize that this is a desirable

// interface to expose to users, but for now it will only be exposed via changes

// to `Get` and `Select`.  The reason that this has been implemented like this is

// this is the only way to not duplicate reflect work in the new API while

// maintaining backwards compatibility.

func scanAll(rows rowsi, dest interface{}, structOnly bool) error {

	var v, vp reflect.Value

	value := reflect.ValueOf(dest)

	// json.Unmarshal returns errors for these

	if value.Kind() != reflect.Ptr {

		return errors.New("must pass a pointer, not a value, to StructScan destination")

	}

	if value.IsNil() {

		return errors.New("nil pointer passed to StructScan destination")

	}

	direct := reflect.Indirect(value)

	slice, err := baseType(value.Type(), reflect.Slice)

	if err != nil {

		return err

	}

	isPtr := slice.Elem().Kind() == reflect.Ptr

	base := reflectx.Deref(slice.Elem())

	scannable := isScannable(base)

	if structOnly && scannable {

		return structOnlyError(base)

	}

	columns, err := rows.Columns()

	if err != nil {

		return err

	}

	// if it's a base type make sure it only has 1 column;  if not return an error

	if scannable && len(columns) > 1 {

		return fmt.Errorf("non-struct dest type %s with >1 columns (%d)", base.Kind(), len(columns))

	}

	if !scannable {

		var values []interface{}

		var m *reflectx.Mapper

		switch rows.(type) {

		case *Rows:

			m = rows.(*Rows).Mapper

		default:

			m = mapper()

		}

		fields := m.TraversalsByName(base, columns)

		// if we are not unsafe and are missing fields, return an error

		if f, err := missingFields(fields); err != nil && !isUnsafe(rows) {

			return fmt.Errorf("missing destination name %s in %T", columns[f], dest)

		}

		values = make([]interface{}, len(columns))

		for rows.Next() {

			// create a new struct type (which returns PtrTo) and indirect it

			vp = reflect.New(base)

			v = reflect.Indirect(vp)

			err = fieldsByTraversal(v, fields, values, true)

			if err != nil {

				return err

			}

			// scan into the struct field pointers and append to our results

			err = rows.Scan(values...)

			if err != nil {

				return err

			}

			if isPtr {

				direct.Set(reflect.Append(direct, vp))

			} else {

				direct.Set(reflect.Append(direct, v))

			}

		}

	} else {

		for rows.Next() {

			vp = reflect.New(base)

			err = rows.Scan(vp.Interface())

			if err != nil {

				return err

			}

			// append

			if isPtr {

				direct.Set(reflect.Append(direct, vp))

			} else {

				direct.Set(reflect.Append(direct, reflect.Indirect(vp)))

			}

		}

	}

	return rows.Err()

}

// FIXME: StructScan was the very first bit of API in sqlx, and now unfortunately

// it doesn't really feel like it's named properly.  There is an incongruency

// between this and the way that StructScan (which might better be ScanStruct

// anyway) works on a rows object.

// StructScan all rows from an sql.Rows or an sqlx.Rows into the dest slice.

// StructScan will scan in the entire rows result, so if you do not want to

// allocate structs for the entire result, use Queryx and see sqlx.Rows.StructScan.

// If rows is sqlx.Rows, it will use its mapper, otherwise it will use the default.

func StructScan(rows rowsi, dest interface{}) error {

	return scanAll(rows, dest, true)

}

// reflect helpers

func baseType(t reflect.Type, expected reflect.Kind) (reflect.Type, error) {

	t = reflectx.Deref(t)

	if t.Kind() != expected {

		return nil, fmt.Errorf("expected %s but got %s", expected, t.Kind())

	}

	return t, nil

}

// fieldsByName fills a values interface with fields from the passed value based

// on the traversals in int.  If ptrs is true, return addresses instead of values.

// We write this instead of using FieldsByName to save allocations and map lookups

// when iterating over many rows.  Empty traversals will get an interface pointer.

// Because of the necessity of requesting ptrs or values, it's considered a bit too

// specialized for inclusion in reflectx itself.

func fieldsByTraversal(v reflect.Value, traversals [][]int, values []interface{}, ptrs bool) error {

	v = reflect.Indirect(v)

	if v.Kind() != reflect.Struct {

		return errors.New("argument not a struct")

	}

	for i, traversal := range traversals {

		if len(traversal) == 0 {

			values[i] = new(interface{})

			continue

		}

		f := reflectx.FieldByIndexes(v, traversal)

		if ptrs {

			values[i] = f.Addr().Interface()

		} else {

			values[i] = f.Interface()

		}

	}

	return nil

}

func missingFields(transversals [][]int) (field int, err error) {

	for i, t := range transversals {

		if len(t) == 0 {

			return i, errors.New("missing field")

		}

	}

	return 0, nil

}