Refactor keys and queries in datastore service and implementation.

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"
 )
 
 // 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
+        KeyForObj(src interface{}) *Key
+
+        // MakeKey is a convenience method for manufacturing a *Key. It should only be
+        // used when elems... is known statically (e.g. in the code) to be correct.
+        //
+        // elems is pairs of (string, string|int|int32|int64) pairs, which correspond
+        // to Kind/id pairs. Example:
+        //   dstore.MakeKey("Parent", 1, "Child", "id")
+        //
+        // Would create the key:
+        //   <current appID>:<current Namespace>:/Parent,1/Child,id
+        //
+        // If elems is not parsable (e.g. wrong length, wrong types, etc.) this method
+        // will panic.
+        MakeKey(elems ...interface{}) *Key

[dnj, 2015/09/18 16:47:57]

WDYT about making these helper methods instead of interface methods? IMO
convenience methods should not belong to the interface.
ds.MakeKey(ctx, ...)

[iannucci, 2015/09/18 22:25:48]

discussed offline; Interface /is/ the convenience method holder :). It could
also probably just be a struct too, since its not actually meant to have more
than one implementation, and the implementation lives in this package anyway...

+
+        // NewKey constructs a new key in the current appID/Namespace, using the
+        // specified parameters.
+        NewKey(kind, stringID string, intID int64, parent *Key) *Key
+
+        // NewKeyToks constructs a new key in the current appID/Namespace, using the
+        // specified key tokens.
+        NewKeyToks([]KeyTok) *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
+        KeyForObjErr(src interface{}) (*Key, error)
 
         // 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
         // retrieved item.
         //
         // cb is a callback function whose signature is
         //   func(obj TYPE, getCursor CursorCB) bool
         //
         // Where TYPE is 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)
+        //   - *Key (implies a keys-only query)
         //
         // Run stops on the first error encountered.
-        Run(q Query, cb interface{}) error
+        Run(q *Query, cb interface{}) error
 
         // DecodeCursor converts a string returned by a Cursor into a Cursor instance.
         // It will return an error if the supplied string is not valid, or could not
         // be decoded by the implementation.
         DecodeCursor(string) (Cursor, 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
+        //   - *[]*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
         //
-        // A Key will be extracted from src via KeyForObj. If
-        // KeyIncomplete(extractedKey) is true, then Put will write the resolved (i.e.
-        // automatic datastore-populated) Key back to src.
+        // A *Key will be extracted from src via KeyForObj. If
+        // extractedKey.Incomplete() is true, then Put will write the resolved (i.e.
+        // automatic datastore-populated) *Key back to src.
         Put(src interface{}) error
 
         // Delete removes an item from the datastore.
-        Delete(key Key) error
+        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
+        DeleteMulti(keys []*Key) error
 
         // Testable returns the Testable interface for the implementation, or nil if
         // there is none.
         Testable() Testable
 
         // 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
 }