mirror of
https://github.com/octoleo/restic.git
synced 2024-12-23 11:28:54 +00:00
455 lines
14 KiB
Go
455 lines
14 KiB
Go
// Copyright 2016 Google Inc. All Rights Reserved.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
/*
|
|
Package datastore provides a client for Google Cloud Datastore.
|
|
|
|
Note: This package is in beta. Some backwards-incompatible changes may occur.
|
|
|
|
|
|
Basic Operations
|
|
|
|
Entities are the unit of storage and are associated with a key. A key
|
|
consists of an optional parent key, a string application ID, a string kind
|
|
(also known as an entity type), and either a StringID or an IntID. A
|
|
StringID is also known as an entity name or key name.
|
|
|
|
It is valid to create a key with a zero StringID and a zero IntID; this is
|
|
called an incomplete key, and does not refer to any saved entity. Putting an
|
|
entity into the datastore under an incomplete key will cause a unique key
|
|
to be generated for that entity, with a non-zero IntID.
|
|
|
|
An entity's contents are a mapping from case-sensitive field names to values.
|
|
Valid value types are:
|
|
- signed integers (int, int8, int16, int32 and int64),
|
|
- bool,
|
|
- string,
|
|
- float32 and float64,
|
|
- []byte (up to 1 megabyte in length),
|
|
- any type whose underlying type is one of the above predeclared types,
|
|
- *Key,
|
|
- GeoPoint,
|
|
- time.Time (stored with microsecond precision),
|
|
- structs whose fields are all valid value types,
|
|
- pointers to structs whose fields are all valid value types,
|
|
- slices of any of the above.
|
|
|
|
Slices of structs are valid, as are structs that contain slices.
|
|
|
|
The Get and Put functions load and save an entity's contents. An entity's
|
|
contents are typically represented by a struct pointer.
|
|
|
|
Example code:
|
|
|
|
type Entity struct {
|
|
Value string
|
|
}
|
|
|
|
func main() {
|
|
ctx := context.Background()
|
|
|
|
// Create a datastore client. In a typical application, you would create
|
|
// a single client which is reused for every datastore operation.
|
|
dsClient, err := datastore.NewClient(ctx, "my-project")
|
|
if err != nil {
|
|
// Handle error.
|
|
}
|
|
|
|
k := datastore.NameKey("Entity", "stringID", nil)
|
|
e := new(Entity)
|
|
if err := dsClient.Get(ctx, k, e); err != nil {
|
|
// Handle error.
|
|
}
|
|
|
|
old := e.Value
|
|
e.Value = "Hello World!"
|
|
|
|
if _, err := dsClient.Put(ctx, k, e); err != nil {
|
|
// Handle error.
|
|
}
|
|
|
|
fmt.Printf("Updated value from %q to %q\n", old, e.Value)
|
|
}
|
|
|
|
GetMulti, PutMulti and DeleteMulti are batch versions of the Get, Put and
|
|
Delete functions. They take a []*Key instead of a *Key, and may return a
|
|
datastore.MultiError when encountering partial failure.
|
|
|
|
|
|
Properties
|
|
|
|
An entity's contents can be represented by a variety of types. These are
|
|
typically struct pointers, but can also be any type that implements the
|
|
PropertyLoadSaver interface. If using a struct pointer, you do not have to
|
|
explicitly implement the PropertyLoadSaver interface; the datastore will
|
|
automatically convert via reflection. If a struct pointer does implement that
|
|
interface then those methods will be used in preference to the default
|
|
behavior for struct pointers. Struct pointers are more strongly typed and are
|
|
easier to use; PropertyLoadSavers are more flexible.
|
|
|
|
The actual types passed do not have to match between Get and Put calls or even
|
|
across different calls to datastore. It is valid to put a *PropertyList and
|
|
get that same entity as a *myStruct, or put a *myStruct0 and get a *myStruct1.
|
|
Conceptually, any entity is saved as a sequence of properties, and is loaded
|
|
into the destination value on a property-by-property basis. When loading into
|
|
a struct pointer, an entity that cannot be completely represented (such as a
|
|
missing field) will result in an ErrFieldMismatch error but it is up to the
|
|
caller whether this error is fatal, recoverable or ignorable.
|
|
|
|
By default, for struct pointers, all properties are potentially indexed, and
|
|
the property name is the same as the field name (and hence must start with an
|
|
upper case letter).
|
|
|
|
Fields may have a `datastore:"name,options"` tag. The tag name is the
|
|
property name, which must be one or more valid Go identifiers joined by ".",
|
|
but may start with a lower case letter. An empty tag name means to just use the
|
|
field name. A "-" tag name means that the datastore will ignore that field.
|
|
|
|
The only valid options are "omitempty", "noindex" and "flatten".
|
|
|
|
If the options include "omitempty" and the value of the field is empty, then the field will be omitted on Save.
|
|
The empty values are false, 0, any nil interface value, and any array, slice, map, or string of length zero.
|
|
Struct field values will never be empty.
|
|
|
|
If options include "noindex" then the field will not be indexed. All fields are indexed
|
|
by default. Strings or byte slices longer than 1500 bytes cannot be indexed;
|
|
fields used to store long strings and byte slices must be tagged with "noindex"
|
|
or they will cause Put operations to fail.
|
|
|
|
For a nested struct field, the options may also include "flatten". This indicates
|
|
that the immediate fields and any nested substruct fields of the nested struct should be
|
|
flattened. See below for examples.
|
|
|
|
To use multiple options together, separate them by a comma.
|
|
The order does not matter.
|
|
|
|
If the options is "" then the comma may be omitted.
|
|
|
|
Example code:
|
|
|
|
// A and B are renamed to a and b.
|
|
// A, C and J are not indexed.
|
|
// D's tag is equivalent to having no tag at all (E).
|
|
// I is ignored entirely by the datastore.
|
|
// J has tag information for both the datastore and json packages.
|
|
type TaggedStruct struct {
|
|
A int `datastore:"a,noindex"`
|
|
B int `datastore:"b"`
|
|
C int `datastore:",noindex"`
|
|
D int `datastore:""`
|
|
E int
|
|
I int `datastore:"-"`
|
|
J int `datastore:",noindex" json:"j"`
|
|
}
|
|
|
|
|
|
Key Field
|
|
|
|
If the struct contains a *datastore.Key field tagged with the name "__key__",
|
|
its value will be ignored on Put. When reading the Entity back into the Go struct,
|
|
the field will be populated with the *datastore.Key value used to query for
|
|
the Entity.
|
|
|
|
Example code:
|
|
|
|
type MyEntity struct {
|
|
A int
|
|
K *datastore.Key `datastore:"__key__"`
|
|
}
|
|
|
|
k := datastore.NameKey("Entity", "stringID", nil)
|
|
e := MyEntity{A: 12}
|
|
k, err = dsClient.Put(ctx, k, e)
|
|
if err != nil {
|
|
// Handle error.
|
|
}
|
|
|
|
var entities []MyEntity
|
|
q := datastore.NewQuery("Entity").Filter("A =", 12).Limit(1)
|
|
_, err := dsClient.GetAll(ctx, q, &entities)
|
|
if err != nil {
|
|
// Handle error
|
|
}
|
|
|
|
log.Println(entities[0])
|
|
// Prints {12 /Entity,stringID}
|
|
|
|
|
|
|
|
Structured Properties
|
|
|
|
If the struct pointed to contains other structs, then the nested or embedded
|
|
structs are themselves saved as Entity values. For example, given these definitions:
|
|
|
|
type Inner struct {
|
|
W int32
|
|
X string
|
|
}
|
|
|
|
type Outer struct {
|
|
I Inner
|
|
}
|
|
|
|
then an Outer would have one property, Inner, encoded as an Entity value.
|
|
|
|
If an outer struct is tagged "noindex" then all of its implicit flattened
|
|
fields are effectively "noindex".
|
|
|
|
If the Inner struct contains a *Key field with the name "__key__", like so:
|
|
|
|
type Inner struct {
|
|
W int32
|
|
X string
|
|
K *datastore.Key `datastore:"__key__"`
|
|
}
|
|
|
|
type Outer struct {
|
|
I Inner
|
|
}
|
|
|
|
then the value of K will be used as the Key for Inner, represented
|
|
as an Entity value in datastore.
|
|
|
|
If any nested struct fields should be flattened, instead of encoded as
|
|
Entity values, the nested struct field should be tagged with the "flatten"
|
|
option. For example, given the following:
|
|
|
|
type Inner1 struct {
|
|
W int32
|
|
X string
|
|
}
|
|
|
|
type Inner2 struct {
|
|
Y float64
|
|
}
|
|
|
|
type Inner3 struct {
|
|
Z bool
|
|
}
|
|
|
|
type Inner4 struct {
|
|
WW int
|
|
}
|
|
|
|
type Inner5 struct {
|
|
X Inner4
|
|
}
|
|
|
|
type Outer struct {
|
|
A int16
|
|
I []Inner1 `datastore:",flatten"`
|
|
J Inner2 `datastore:",flatten"`
|
|
K Inner5 `datastore:",flatten"`
|
|
Inner3 `datastore:",flatten"`
|
|
}
|
|
|
|
an Outer's properties would be equivalent to those of:
|
|
|
|
type OuterEquivalent struct {
|
|
A int16
|
|
IDotW []int32 `datastore:"I.W"`
|
|
IDotX []string `datastore:"I.X"`
|
|
JDotY float64 `datastore:"J.Y"`
|
|
KDotXDotWW int `datastore:"K.X.WW"`
|
|
Z bool
|
|
}
|
|
|
|
Note that the "flatten" option cannot be used for Entity value fields.
|
|
The server will reject any dotted field names for an Entity value.
|
|
|
|
|
|
The PropertyLoadSaver Interface
|
|
|
|
An entity's contents can also be represented by any type that implements the
|
|
PropertyLoadSaver interface. This type may be a struct pointer, but it does
|
|
not have to be. The datastore package will call Load when getting the entity's
|
|
contents, and Save when putting the entity's contents.
|
|
Possible uses include deriving non-stored fields, verifying fields, or indexing
|
|
a field only if its value is positive.
|
|
|
|
Example code:
|
|
|
|
type CustomPropsExample struct {
|
|
I, J int
|
|
// Sum is not stored, but should always be equal to I + J.
|
|
Sum int `datastore:"-"`
|
|
}
|
|
|
|
func (x *CustomPropsExample) Load(ps []datastore.Property) error {
|
|
// Load I and J as usual.
|
|
if err := datastore.LoadStruct(x, ps); err != nil {
|
|
return err
|
|
}
|
|
// Derive the Sum field.
|
|
x.Sum = x.I + x.J
|
|
return nil
|
|
}
|
|
|
|
func (x *CustomPropsExample) Save() ([]datastore.Property, error) {
|
|
// Validate the Sum field.
|
|
if x.Sum != x.I + x.J {
|
|
return nil, errors.New("CustomPropsExample has inconsistent sum")
|
|
}
|
|
// Save I and J as usual. The code below is equivalent to calling
|
|
// "return datastore.SaveStruct(x)", but is done manually for
|
|
// demonstration purposes.
|
|
return []datastore.Property{
|
|
{
|
|
Name: "I",
|
|
Value: int64(x.I),
|
|
},
|
|
{
|
|
Name: "J",
|
|
Value: int64(x.J),
|
|
},
|
|
}, nil
|
|
}
|
|
|
|
The *PropertyList type implements PropertyLoadSaver, and can therefore hold an
|
|
arbitrary entity's contents.
|
|
|
|
The KeyLoader Interface
|
|
|
|
If a type implements the PropertyLoadSaver interface, it may
|
|
also want to implement the KeyLoader interface.
|
|
The KeyLoader interface exists to allow implementations of PropertyLoadSaver
|
|
to also load an Entity's Key into the Go type. This type may be a struct
|
|
pointer, but it does not have to be. The datastore package will call LoadKey
|
|
when getting the entity's contents, after calling Load.
|
|
|
|
Example code:
|
|
|
|
type WithKeyExample struct {
|
|
I int
|
|
Key *datastore.Key
|
|
}
|
|
|
|
func (x *WithKeyExample) LoadKey(k *datastore.Key) error {
|
|
x.Key = k
|
|
return nil
|
|
}
|
|
|
|
func (x *WithKeyExample) Load(ps []datastore.Property) error {
|
|
// Load I as usual.
|
|
return datastore.LoadStruct(x, ps)
|
|
}
|
|
|
|
func (x *WithKeyExample) Save() ([]datastore.Property, error) {
|
|
// Save I as usual.
|
|
return datastore.SaveStruct(x)
|
|
}
|
|
|
|
To load a Key into a struct which does not implement the PropertyLoadSaver
|
|
interface, see the "Key Field" section above.
|
|
|
|
|
|
Queries
|
|
|
|
Queries retrieve entities based on their properties or key's ancestry. Running
|
|
a query yields an iterator of results: either keys or (key, entity) pairs.
|
|
Queries are re-usable and it is safe to call Query.Run from concurrent
|
|
goroutines. Iterators are not safe for concurrent use.
|
|
|
|
Queries are immutable, and are either created by calling NewQuery, or derived
|
|
from an existing query by calling a method like Filter or Order that returns a
|
|
new query value. A query is typically constructed by calling NewQuery followed
|
|
by a chain of zero or more such methods. These methods are:
|
|
- Ancestor and Filter constrain the entities returned by running a query.
|
|
- Order affects the order in which they are returned.
|
|
- Project constrains the fields returned.
|
|
- Distinct de-duplicates projected entities.
|
|
- KeysOnly makes the iterator return only keys, not (key, entity) pairs.
|
|
- Start, End, Offset and Limit define which sub-sequence of matching entities
|
|
to return. Start and End take cursors, Offset and Limit take integers. Start
|
|
and Offset affect the first result, End and Limit affect the last result.
|
|
If both Start and Offset are set, then the offset is relative to Start.
|
|
If both End and Limit are set, then the earliest constraint wins. Limit is
|
|
relative to Start+Offset, not relative to End. As a special case, a
|
|
negative limit means unlimited.
|
|
|
|
Example code:
|
|
|
|
type Widget struct {
|
|
Description string
|
|
Price int
|
|
}
|
|
|
|
func printWidgets(ctx context.Context, client *datastore.Client) {
|
|
q := datastore.NewQuery("Widget").
|
|
Filter("Price <", 1000).
|
|
Order("-Price")
|
|
for t := client.Run(ctx, q); ; {
|
|
var x Widget
|
|
key, err := t.Next(&x)
|
|
if err == iterator.Done {
|
|
break
|
|
}
|
|
if err != nil {
|
|
// Handle error.
|
|
}
|
|
fmt.Printf("Key=%v\nWidget=%#v\n\n", key, x)
|
|
}
|
|
}
|
|
|
|
|
|
Transactions
|
|
|
|
Client.RunInTransaction runs a function in a transaction.
|
|
|
|
Example code:
|
|
|
|
type Counter struct {
|
|
Count int
|
|
}
|
|
|
|
func incCount(ctx context.Context, client *datastore.Client) {
|
|
var count int
|
|
key := datastore.NameKey("Counter", "singleton", nil)
|
|
_, err := client.RunInTransaction(ctx, func(tx *datastore.Transaction) error {
|
|
var x Counter
|
|
if err := tx.Get(key, &x); err != nil && err != datastore.ErrNoSuchEntity {
|
|
return err
|
|
}
|
|
x.Count++
|
|
if _, err := tx.Put(key, &x); err != nil {
|
|
return err
|
|
}
|
|
count = x.Count
|
|
return nil
|
|
})
|
|
if err != nil {
|
|
// Handle error.
|
|
}
|
|
// The value of count is only valid once the transaction is successful
|
|
// (RunInTransaction has returned nil).
|
|
fmt.Printf("Count=%d\n", count)
|
|
}
|
|
|
|
Google Cloud Datastore Emulator
|
|
|
|
This package supports the Cloud Datastore emulator, which is useful for testing and
|
|
development. Environment variables are used to indicate that datastore traffic should be
|
|
directed to the emulator instead of the production Datastore service.
|
|
|
|
To install and set up the emulator and its environment variables, see the documentation
|
|
at https://cloud.google.com/datastore/docs/tools/datastore-emulator.
|
|
|
|
Authentication
|
|
|
|
See examples of authorization and authentication at
|
|
https://godoc.org/cloud.google.com/go#pkg-examples.
|
|
|
|
*/
|
|
package datastore // import "cloud.google.com/go/datastore"
|