294 lines
8.5 KiB
Go
294 lines
8.5 KiB
Go
// Copyright 2011 Google Inc. All rights reserved.
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// Use of this source code is governed by the Apache 2.0
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// license that can be found in the LICENSE file.
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package datastore
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import (
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"fmt"
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"reflect"
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"strings"
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"sync"
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"unicode"
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)
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// Entities with more than this many indexed properties will not be saved.
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const maxIndexedProperties = 20000
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// []byte fields more than 1 megabyte long will not be loaded or saved.
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const maxBlobLen = 1 << 20
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// Property is a name/value pair plus some metadata. A datastore entity's
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// contents are loaded and saved as a sequence of Properties. An entity can
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// have multiple Properties with the same name, provided that p.Multiple is
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// true on all of that entity's Properties with that name.
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type Property struct {
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// Name is the property name.
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Name string
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// Value is the property value. The valid types are:
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// - int64
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// - bool
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// - string
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// - float64
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// - ByteString
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// - *Key
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// - time.Time
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// - appengine.BlobKey
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// - appengine.GeoPoint
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// - []byte (up to 1 megabyte in length)
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// This set is smaller than the set of valid struct field types that the
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// datastore can load and save. A Property Value cannot be a slice (apart
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// from []byte); use multiple Properties instead. Also, a Value's type
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// must be explicitly on the list above; it is not sufficient for the
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// underlying type to be on that list. For example, a Value of "type
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// myInt64 int64" is invalid. Smaller-width integers and floats are also
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// invalid. Again, this is more restrictive than the set of valid struct
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// field types.
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//
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// A Value will have an opaque type when loading entities from an index,
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// such as via a projection query. Load entities into a struct instead
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// of a PropertyLoadSaver when using a projection query.
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//
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// A Value may also be the nil interface value; this is equivalent to
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// Python's None but not directly representable by a Go struct. Loading
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// a nil-valued property into a struct will set that field to the zero
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// value.
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Value interface{}
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// NoIndex is whether the datastore cannot index this property.
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NoIndex bool
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// Multiple is whether the entity can have multiple properties with
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// the same name. Even if a particular instance only has one property with
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// a certain name, Multiple should be true if a struct would best represent
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// it as a field of type []T instead of type T.
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Multiple bool
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}
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// ByteString is a short byte slice (up to 1500 bytes) that can be indexed.
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type ByteString []byte
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// PropertyLoadSaver can be converted from and to a slice of Properties.
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type PropertyLoadSaver interface {
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Load([]Property) error
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Save() ([]Property, error)
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}
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// PropertyList converts a []Property to implement PropertyLoadSaver.
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type PropertyList []Property
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var (
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typeOfPropertyLoadSaver = reflect.TypeOf((*PropertyLoadSaver)(nil)).Elem()
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typeOfPropertyList = reflect.TypeOf(PropertyList(nil))
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)
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// Load loads all of the provided properties into l.
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// It does not first reset *l to an empty slice.
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func (l *PropertyList) Load(p []Property) error {
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*l = append(*l, p...)
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return nil
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}
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// Save saves all of l's properties as a slice or Properties.
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func (l *PropertyList) Save() ([]Property, error) {
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return *l, nil
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}
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// validPropertyName returns whether name consists of one or more valid Go
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// identifiers joined by ".".
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func validPropertyName(name string) bool {
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if name == "" {
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return false
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}
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for _, s := range strings.Split(name, ".") {
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if s == "" {
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return false
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}
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first := true
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for _, c := range s {
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if first {
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first = false
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if c != '_' && !unicode.IsLetter(c) {
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return false
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}
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} else {
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if c != '_' && !unicode.IsLetter(c) && !unicode.IsDigit(c) {
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return false
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}
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}
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}
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}
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return true
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}
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// structTag is the parsed `datastore:"name,options"` tag of a struct field.
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// If a field has no tag, or the tag has an empty name, then the structTag's
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// name is just the field name. A "-" name means that the datastore ignores
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// that field.
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type structTag struct {
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name string
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noIndex bool
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}
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// structCodec describes how to convert a struct to and from a sequence of
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// properties.
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type structCodec struct {
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// byIndex gives the structTag for the i'th field.
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byIndex []structTag
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// byName gives the field codec for the structTag with the given name.
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byName map[string]fieldCodec
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// hasSlice is whether a struct or any of its nested or embedded structs
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// has a slice-typed field (other than []byte).
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hasSlice bool
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// complete is whether the structCodec is complete. An incomplete
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// structCodec may be encountered when walking a recursive struct.
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complete bool
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}
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// fieldCodec is a struct field's index and, if that struct field's type is
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// itself a struct, that substruct's structCodec.
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type fieldCodec struct {
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index int
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substructCodec *structCodec
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}
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// structCodecs collects the structCodecs that have already been calculated.
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var (
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structCodecsMutex sync.Mutex
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structCodecs = make(map[reflect.Type]*structCodec)
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)
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// getStructCodec returns the structCodec for the given struct type.
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func getStructCodec(t reflect.Type) (*structCodec, error) {
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structCodecsMutex.Lock()
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defer structCodecsMutex.Unlock()
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return getStructCodecLocked(t)
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}
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// getStructCodecLocked implements getStructCodec. The structCodecsMutex must
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// be held when calling this function.
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func getStructCodecLocked(t reflect.Type) (ret *structCodec, retErr error) {
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c, ok := structCodecs[t]
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if ok {
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return c, nil
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}
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c = &structCodec{
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byIndex: make([]structTag, t.NumField()),
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byName: make(map[string]fieldCodec),
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}
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// Add c to the structCodecs map before we are sure it is good. If t is
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// a recursive type, it needs to find the incomplete entry for itself in
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// the map.
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structCodecs[t] = c
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defer func() {
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if retErr != nil {
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delete(structCodecs, t)
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}
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}()
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for i := range c.byIndex {
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f := t.Field(i)
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name, opts := f.Tag.Get("datastore"), ""
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if i := strings.Index(name, ","); i != -1 {
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name, opts = name[:i], name[i+1:]
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}
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if name == "" {
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if !f.Anonymous {
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name = f.Name
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}
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} else if name == "-" {
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c.byIndex[i] = structTag{name: name}
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continue
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} else if !validPropertyName(name) {
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return nil, fmt.Errorf("datastore: struct tag has invalid property name: %q", name)
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}
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substructType, fIsSlice := reflect.Type(nil), false
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switch f.Type.Kind() {
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case reflect.Struct:
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substructType = f.Type
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case reflect.Slice:
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if f.Type.Elem().Kind() == reflect.Struct {
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substructType = f.Type.Elem()
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}
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fIsSlice = f.Type != typeOfByteSlice
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c.hasSlice = c.hasSlice || fIsSlice
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}
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if substructType != nil && substructType != typeOfTime && substructType != typeOfGeoPoint {
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if name != "" {
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name = name + "."
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}
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sub, err := getStructCodecLocked(substructType)
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if err != nil {
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return nil, err
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}
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if !sub.complete {
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return nil, fmt.Errorf("datastore: recursive struct: field %q", f.Name)
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}
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if fIsSlice && sub.hasSlice {
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return nil, fmt.Errorf(
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"datastore: flattening nested structs leads to a slice of slices: field %q", f.Name)
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}
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c.hasSlice = c.hasSlice || sub.hasSlice
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for relName := range sub.byName {
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absName := name + relName
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if _, ok := c.byName[absName]; ok {
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return nil, fmt.Errorf("datastore: struct tag has repeated property name: %q", absName)
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}
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c.byName[absName] = fieldCodec{index: i, substructCodec: sub}
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}
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} else {
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if _, ok := c.byName[name]; ok {
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return nil, fmt.Errorf("datastore: struct tag has repeated property name: %q", name)
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}
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c.byName[name] = fieldCodec{index: i}
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}
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c.byIndex[i] = structTag{
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name: name,
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noIndex: opts == "noindex",
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}
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}
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c.complete = true
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return c, nil
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}
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// structPLS adapts a struct to be a PropertyLoadSaver.
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type structPLS struct {
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v reflect.Value
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codec *structCodec
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}
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// newStructPLS returns a PropertyLoadSaver for the struct pointer p.
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func newStructPLS(p interface{}) (PropertyLoadSaver, error) {
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v := reflect.ValueOf(p)
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if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct {
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return nil, ErrInvalidEntityType
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}
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v = v.Elem()
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codec, err := getStructCodec(v.Type())
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if err != nil {
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return nil, err
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}
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return structPLS{v, codec}, nil
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}
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// LoadStruct loads the properties from p to dst.
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// dst must be a struct pointer.
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func LoadStruct(dst interface{}, p []Property) error {
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x, err := newStructPLS(dst)
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if err != nil {
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return err
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}
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return x.Load(p)
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}
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// SaveStruct returns the properties from src as a slice of Properties.
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// src must be a struct pointer.
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func SaveStruct(src interface{}) ([]Property, error) {
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x, err := newStructPLS(src)
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if err != nil {
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return nil, err
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}
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return x.Save()
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}
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