Add 'user friendly' datastore API.

service/datastore/interface.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package datastore
+
+import (
+        "golang.org/x/net/context"
+)
+
+// RunCB is the callback signature provided to Interface.Run
+//
+//   - obj is an object as specified by the proto argument of Run
+//   - getCursor can be invoked to obtain the current cursor.
+//
+// Return true to continue iterating through the query results, or false to stop.
+type RunCB func(obj interface{}, getCursor func() (Cursor, error)) bool
+
+// Interface is the 'user-friendly' interface to access the current filtered
+// datastore service implementation.
+//
+// Note that in exchange for userfriendliness, this interface ends up doing
+// a lot of reflection.
+//
+// Methods taking 'interface{}' objects describe what a valid type for that
+// interface are in the comments.
+//
+// Struct objects passed in will be converted to PropertyLoadSaver interfaces
+// using this package's GetPLS function.
+type Interface interface {
+        // NewKey produces a new Key with the current appid and namespace.
+        NewKey(kind, stringID string, intID int64, parent Key) Key
+
+        // KeyForObj extracts a key from src.
+        //
+        // It is the same as KeyForObjErr, except that if KeyForObjErr would have
+        // returned an error, this method panics. It's safe to use if you know that
+        // src statically meets the metadata constraints described by KeyForObjErr.
+        KeyForObj(src interface{}) Key
+
+        // KeyForObjErr extracts a key from src.
+        //
+        // src must be one of:
+        //   - *S where S is a struct
+        //   - a PropertyLoadSaver
+        //
+        // It is expected that the struct or PropertyLoadSaver exposes the
+        // following metadata (as retrieved by PropertyLoadSaver.GetMeta):
+        //   - "key" (type: Key) - The full datastore key to use. Must not be nil.
+        //     OR
+        //   - "id" (type: int64 or string) - The id of the Key to create
+        //   - "kind" (optional, type: string) - The kind of the Key to create. If
+        //     blank or not present, KeyForObjErr will extract the name of the src
+        //     object's type.
+        //   - "parent" (optional, type: Key) - The parent key to use.
+        //
+        // If a required metadata item is missing or of the wrong type, then this will
+        // return an error.
+        KeyForObjErr(src interface{}) (Key, error)
+
+        // DecodeKey decodes a proto-encoded key.
+        //
+        // The encoding is defined by the appengine SDK's implementation.  In
+        // particular, it is a no-pad-base64-encoded protobuf. If there's an error
+        // during the decoding process, it will be returned.
+        DecodeKey(encoded string) (Key, error)
+
+        // NewQuery creates a new Query object. No server communication occurs.
+        NewQuery(kind string) Query
+
+        // RunInTransaction runs f inside of a transaction. See the appengine SDK's
+        // documentation for full details on the behavior of transactions in the
+        // datastore.
+        //
+        // Note that the behavior of transactions may change depending on what filters
+        // have been installed. It's possible that we'll end up implementing things
+        // like nested/buffered transactions as filters.
+        RunInTransaction(f func(c context.Context) error, opts *TransactionOptions) error
+
+        // Run executes the given query, and calls `cb` for each successfully item.
+        //
+        // proto is a prototype of the objects which will be passed to the callback.
+        // It will be used solely for type information, and the actual proto object
+        // may be zero/nil.  It must be of the form:
+        //   - S or *S where S is a struct
+        //   - P or *P where *P is a concrete type implementing PropertyLoadSaver
+        //   - *Key implies a keys-only query (and cb will be invoked with Key objects)
+        // Run will create a new, populated instance of proto for each call of
+        // cb. Run stops on the first error encountered.
+        Run(q Query, proto interface{}, cb RunCB) error
+
+        // GetAll retrieves all of the Query results into dst.
+        //
+        // dst must be one of:
+        //   - *[]S or *[]*S where S is a struct
+        //   - *[]P or *[]*P where *P is a concrete type implementing PropertyLoadSaver
+        //   - *[]Key implies a keys-only query.
+        GetAll(q Query, dst interface{}) error
+
+        // Get retrieves a single object from the datastore
+        //
+        // dst must be one of:
+        //   - *S where S is a struct
+        //   - *P where *P is a concrete type implementing PropertyLoadSaver
+        Get(dst interface{}) error
+
+        // Put inserts a single object into the datastore
+        //
+        // src must be one of:
+        //   - *S where S is a struct
+        //   - *P where *P is a concrete type implementing PropertyLoadSaver
+        //
+        // If src resolves to an Incomplete key, Put will write the
+        // resolved key back to src.
+        Put(src interface{}) error
+
+        // Delete removes an item from the datastore.
+        Delete(key Key) error
+
+        // GetMulti retrieves items from the datastore.
+        //
+        // dst must be one of:
+        //   - []S or []*S where S is a struct
+        //   - []P or []*P where *P is a concrete type implementing PropertyLoadSaver
+        //   - []I where I is some interface type. Each element of the slice must
+        //               be non-nil, and its underlying type must be either *S or *P.
+        GetMulti(dst interface{}) error
+
+        // PutMulti writes items to the datastore.
+        //
+        // src must be one of:
+        //   - []S or []*S where S is a struct
+        //   - []P or []*P where *P is a concrete type implementing PropertyLoadSaver
+        //   - []I where i is some interface type. Each elemet of the slice must
+        //     be non-nil, and its underlying type must be either *S or *P.
+        //
+        // If items in src resolve to Incomplete keys, PutMulti will write the
+        // resolved keys back to the items in src.
+        PutMulti(src interface{}) error
+
+        // DeleteMulti removes items from the datastore.
+        DeleteMulti(keys []Key) error
+
+        // Raw returns the underlying RawInterface. The Interface and RawInterface may
+        // be used interchangably; there's no danger of interleaving access to the
+        // datastore via the two.
+        Raw() RawInterface
+}