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package application import ( "database/sql" "errors" "fmt" "reflect" "runtime" "strings" "sync" ) // 将结果scan至结构体，copy至 sqlx库: https://github.com/jmoiron/sqlx func scanAll(rows *sql.Rows, 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 } direct.SetLen(0) isPtr := slice.Elem().Kind() == reflect.Ptr base := 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 *Mapper = 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 { 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() } func baseType(t reflect.Type, expected reflect.Kind) (reflect.Type, error) { t = Deref(t) if t.Kind() != expected { return nil, fmt.Errorf("expected %s but got %s", expected, t.Kind()) } return t, nil } // 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()) } var _scannerInterface = reflect.TypeOf((*sql.Scanner)(nil)).Elem() 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 return len(mapper().TypeMap(t).Index) == 0 } 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 *Mapper // mprMu protects mpr. var mprMu sync.Mutex // mapper returns a valid mapper using the configured NameMapper func. func mapper() *Mapper { mprMu.Lock() defer mprMu.Unlock() if mpr == nil { mpr = NewMapperFunc("db", NameMapper) } else if origMapper != reflect.ValueOf(NameMapper) { // if NameMapper has changed, create a new mapper mpr = NewMapperFunc("db", NameMapper) origMapper = reflect.ValueOf(NameMapper) } return mpr } 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 } // 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 := FieldByIndexes(v, traversal) if ptrs { values[i] = f.Addr().Interface() } else { values[i] = f.Interface() } } return nil } // A FieldInfo is metadata for a struct field. type FieldInfo struct { Index []int Path string Field reflect.StructField Zero reflect.Value Name string Options map[string]string Embedded bool Children []*FieldInfo Parent *FieldInfo } // A StructMap is an index of field metadata for a struct. type StructMap struct { Tree *FieldInfo Index []*FieldInfo Paths map[string]*FieldInfo Names map[string]*FieldInfo } // GetByPath returns a *FieldInfo for a given string path. func (f StructMap) GetByPath(path string) *FieldInfo { return f.Paths[path] } // GetByTraversal returns a *FieldInfo for a given integer path. It is // analogous to reflect.FieldByIndex, but using the cached traversal // rather than re-executing the reflect machinery each time. func (f StructMap) GetByTraversal(index []int) *FieldInfo { if len(index) == 0 { return nil } tree := f.Tree for _, i := range index { if i >= len(tree.Children) || tree.Children[i] == nil { return nil } tree = tree.Children[i] } return tree } // Mapper is a general purpose mapper of names to struct fields. A Mapper // behaves like most marshallers in the standard library, obeying a field tag // for name mapping but also providing a basic transform function. type Mapper struct { cache map[reflect.Type]*StructMap tagName string tagMapFunc func(string) string mapFunc func(string) string mutex sync.Mutex } // NewMapper returns a new mapper using the tagName as its struct field tag. // If tagName is the empty string, it is ignored. func NewMapper(tagName string) *Mapper { return &Mapper{ cache: make(map[reflect.Type]*StructMap), tagName: tagName, } } // NewMapperTagFunc returns a new mapper which contains a mapper for field names // AND a mapper for tag values. This is useful for tags like json which can // have values like "name,omitempty". func NewMapperTagFunc(tagName string, mapFunc, tagMapFunc func(string) string) *Mapper { return &Mapper{ cache: make(map[reflect.Type]*StructMap), tagName: tagName, mapFunc: mapFunc, tagMapFunc: tagMapFunc, } } // NewMapperFunc returns a new mapper which optionally obeys a field tag and // a struct field name mapper func given by f. Tags will take precedence, but // for any other field, the mapped name will be f(field.Name) func NewMapperFunc(tagName string, f func(string) string) *Mapper { return &Mapper{ cache: make(map[reflect.Type]*StructMap), tagName: tagName, mapFunc: f, } } // TypeMap returns a mapping of field strings to int slices representing // the traversal down the struct to reach the field. func (m *Mapper) TypeMa