datastore: refactor in preparation for loading nested entity values
This change is a mirror of the same change submitted to
cloud.google.com/go/datastore, the goal being to keep the two packages
as similar as possible.
This change does not alter the black-box/user-facing behavior of the
datastore package.
Refactors:
load() is now able to load nested structs both with flattened field
values (eg. "A.B.C") and nested entities (eg. "A").
structCodec has been refactored in several ways:
1. we only need to store one copy of all the fields (now named 'fields'),
instead of 2 copies ('byName' and 'byIndex').
2. we now store the 'index' of a field in fieldCodec as 'path' (a
slice of indicies) to better acommodate anonymous, nested struct fields.
3. we no longer store unexported fields in the structCodecs, as they are
never used anyway.
4. nested structs are saved in structCodec as "A" (pointing to the
structCodec of field A), instead of "A.B" (pointing to the structCodec
of A) to de-dupe entries with the same index and same struct codec.
Change-Id: I5288dfbffe03e6a8d8ff416707591d3eecb52b28
This repository supports the Go runtime on App Engine, including both the standard App Engine and the “App Engine flexible environment” (formerly known as “Managed VMs”). It provides APIs for interacting with App Engine services. Its canonical import path is google.golang.org/appengine.
See https://cloud.google.com/appengine/docs/go/ for more information.
File issue reports and feature requests on the Google App Engine issue tracker.
The top level directory of this repository is the appengine package. It contains the basic APIs (e.g. appengine.NewContext) that apply across APIs. Specific API packages are in subdirectories (e.g. datastore).
There is an internal subdirectory that contains service protocol buffers, plus packages required for connectivity to make API calls. App Engine apps should not directly import any package under internal.
This section describes how to update an older Go App Engine app to use these packages. A provided tool, aefix, can help automate steps 2 and 3 (run go get google.golang.org/appengine/cmd/aefix to install it), but read the details below since aefix can't perform all the changes.
The app.yaml file (and YAML files for modules) should have these new lines added:
vm: true
See https://cloud.google.com/appengine/docs/go/modules/#Go_Instance_scaling_and_class for details.
The import paths for App Engine packages are now fully qualified, based at google.golang.org/appengine. You will need to update your code to use import paths starting with that; for instance, code importing appengine/datastore will now need to import google.golang.org/appengine/datastore.
Most App Engine services are available with exactly the same API. A few APIs were cleaned up, and some are not available yet. This list summarises the differences:
appengine.Context has been replaced with the Context type from golang.org/x/net/context.appengine.Context are now functions in google.golang.org/appengine/log.appengine.Timeout has been removed. Use context.WithTimeout instead.appengine.Datacenter now takes a context.Context argument.datastore.PropertyLoadSaver has been simplified to use slices in place of channels.delay.Call now returns an error.search.FieldLoadSaver now handles document metadata.urlfetch.Transport no longer has a Deadline field; set a deadline on the context.Context instead.aetest no longer declares its own Context type, and uses the standard one instead.taskqueue.QueueStats no longer takes a maxTasks argument. That argument has been deprecated and unused for a long time.appengine.BackendHostname and appengine.BackendInstance were for the deprecated backends feature. Use appengine.ModuleHostnameand appengine.ModuleName instead.appengine/file and parts of appengine/blobstore are deprecated. Use Google Cloud Storage if the feature you require is not present in the new blobstore package.appengine/socket is not required on App Engine flexible environment / Managed VMs. Use the standard net package instead.