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rows.go
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rows.go
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// Copyright 2016 Qiang Xue. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package dbx
import (
"database/sql"
"reflect"
)
// VarTypeError indicates a variable type error when trying to populating a variable with DB result.
type VarTypeError string
// Error returns the error message.
func (s VarTypeError) Error() string {
return "Invalid variable type: " + string(s)
}
// NullStringMap is a map of sql.NullString that can be used to hold DB query result.
// The map keys correspond to the DB column names, while the map values are their corresponding column values.
type NullStringMap map[string]sql.NullString
// Rows enhances sql.Rows by providing additional data query methods.
// Rows can be obtained by calling Query.Rows(). It is mainly used to populate data row by row.
type Rows struct {
*sql.Rows
fieldMapFunc FieldMapFunc
}
// ScanMap populates the current row of data into a NullStringMap.
// Note that the NullStringMap must not be nil, or it will panic.
// The NullStringMap will be populated using column names as keys and their values as
// the corresponding element values.
func (r *Rows) ScanMap(a NullStringMap) error {
cols, _ := r.Columns()
var refs []interface{}
for i := 0; i < len(cols); i++ {
var t sql.NullString
refs = append(refs, &t)
}
if err := r.Scan(refs...); err != nil {
return err
}
for i, col := range cols {
a[col] = *refs[i].(*sql.NullString)
}
return nil
}
// ScanStruct populates the current row of data into a struct.
// The struct must be given as a pointer.
//
// ScanStruct associates struct fields with DB table columns through a field mapping function.
// It populates a struct field with the data of its associated column.
// Note that only exported struct fields will be populated.
//
// By default, DefaultFieldMapFunc() is used to map struct fields to table columns.
// This function separates each word in a field name with a underscore and turns every letter into lower case.
// For example, "LastName" is mapped to "last_name", "MyID" is mapped to "my_id", and so on.
// To change the default behavior, set DB.FieldMapper with your custom mapping function.
// You may also set Query.FieldMapper to change the behavior for particular queries.
func (r *Rows) ScanStruct(a interface{}) error {
rv := reflect.ValueOf(a)
if rv.Kind() != reflect.Ptr || rv.IsNil() {
return VarTypeError("must be a pointer")
}
rv = indirect(rv)
if rv.Kind() != reflect.Struct {
return VarTypeError("must be a pointer to a struct")
}
si := getStructInfo(rv.Type(), r.fieldMapFunc)
cols, _ := r.Columns()
refs := make([]interface{}, len(cols))
for i, col := range cols {
if fi, ok := si.dbNameMap[col]; ok {
refs[i] = fi.getField(rv).Addr().Interface()
} else {
refs[i] = &sql.NullString{}
}
}
if err := r.Scan(refs...); err != nil {
return err
}
// check for PostScanner
if rv.CanAddr() {
addr := rv.Addr()
if addr.CanInterface() {
if ps, ok := addr.Interface().(PostScanner); ok {
if err := ps.PostScan(); err != nil {
return err
}
}
}
}
return nil
}
// all populates all rows of query result into a slice of struct or NullStringMap.
// Note that the slice must be given as a pointer.
func (r *Rows) all(slice interface{}) error {
defer r.Close()
v := reflect.ValueOf(slice)
if v.Kind() != reflect.Ptr || v.IsNil() {
return VarTypeError("must be a pointer")
}
v = indirect(v)
if v.Kind() != reflect.Slice {
return VarTypeError("must be a slice of struct or NullStringMap")
}
if v.IsNil() {
// create an empty slice
v.Set(reflect.MakeSlice(v.Type(), 0, 0))
}
et := v.Type().Elem()
if et.Kind() == reflect.Map {
for r.Next() {
ev, ok := reflect.MakeMap(et).Interface().(NullStringMap)
if !ok {
return VarTypeError("must be a slice of struct or NullStringMap")
}
if err := r.ScanMap(ev); err != nil {
return err
}
v.Set(reflect.Append(v, reflect.ValueOf(ev)))
}
return r.Close()
}
var isSliceOfPointers bool
if et.Kind() == reflect.Ptr {
isSliceOfPointers = true
et = et.Elem()
}
if et.Kind() != reflect.Struct {
return VarTypeError("must be a slice of struct or NullStringMap")
}
etPtr := reflect.PtrTo(et)
implementsPostScanner := etPtr.Implements(postScannerType)
si := getStructInfo(et, r.fieldMapFunc)
cols, _ := r.Columns()
for r.Next() {
ev := reflect.New(et).Elem()
refs := make([]interface{}, len(cols))
for i, col := range cols {
if fi, ok := si.dbNameMap[col]; ok {
refs[i] = fi.getField(ev).Addr().Interface()
} else {
refs[i] = &sql.NullString{}
}
}
if err := r.Scan(refs...); err != nil {
return err
}
if isSliceOfPointers {
ev = ev.Addr()
}
// check for PostScanner
if implementsPostScanner {
evAddr := ev
if ev.CanAddr() {
evAddr = ev.Addr()
}
if evAddr.CanInterface() {
if ps, ok := evAddr.Interface().(PostScanner); ok {
if err := ps.PostScan(); err != nil {
return err
}
}
}
}
v.Set(reflect.Append(v, ev))
}
return r.Close()
}
// column populates the given slice with the first column of the query result.
// Note that the slice must be given as a pointer.
func (r *Rows) column(slice interface{}) error {
defer r.Close()
v := reflect.ValueOf(slice)
if v.Kind() != reflect.Ptr || v.IsNil() {
return VarTypeError("must be a pointer to a slice")
}
v = indirect(v)
if v.Kind() != reflect.Slice {
return VarTypeError("must be a pointer to a slice")
}
et := v.Type().Elem()
cols, _ := r.Columns()
for r.Next() {
ev := reflect.New(et)
refs := make([]interface{}, len(cols))
for i := range cols {
if i == 0 {
refs[i] = ev.Interface()
} else {
refs[i] = &sql.NullString{}
}
}
if err := r.Scan(refs...); err != nil {
return err
}
v.Set(reflect.Append(v, ev.Elem()))
}
return r.Close()
}
// one populates a single row of query result into a struct or a NullStringMap.
// Note that if a struct is given, it should be a pointer.
func (r *Rows) one(a interface{}) error {
defer r.Close()
if !r.Next() {
if err := r.Err(); err != nil {
return err
}
return sql.ErrNoRows
}
var err error
rt := reflect.TypeOf(a)
if rt.Kind() == reflect.Ptr && rt.Elem().Kind() == reflect.Map {
// pointer to map
v := indirect(reflect.ValueOf(a))
if v.IsNil() {
v.Set(reflect.MakeMap(v.Type()))
}
a = v.Interface()
rt = reflect.TypeOf(a)
}
if rt.Kind() == reflect.Map {
v, ok := a.(NullStringMap)
if !ok {
return VarTypeError("must be a NullStringMap")
}
if v == nil {
return VarTypeError("NullStringMap is nil")
}
err = r.ScanMap(v)
} else {
err = r.ScanStruct(a)
}
if err != nil {
return err
}
return r.Close()
}
// row populates a single row of query result into a list of variables.
func (r *Rows) row(a ...interface{}) error {
defer r.Close()
for _, dp := range a {
if _, ok := dp.(*sql.RawBytes); ok {
return VarTypeError("RawBytes isn't allowed on Row()")
}
}
if !r.Next() {
if err := r.Err(); err != nil {
return err
}
return sql.ErrNoRows
}
if err := r.Scan(a...); err != nil {
return err
}
return r.Close()
}