// Copyright 2017 Google LLC
//
// 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.

// DO NOT EDIT doc.go. Modify internal/doc.template, then run make -C internal.

/*
Package firestore provides a client for reading and writing to a Cloud Firestore
database.

See https://cloud.google.com/firestore/docs for an introduction
to Cloud Firestore and additional help on using the Firestore API.

Note: you can't use both Cloud Firestore and Cloud Datastore in the same
project.

Creating a Client

To start working with this package, create a client with a project ID:

[NewClient]

CollectionRefs and DocumentRefs

In Firestore, documents are sets of key-value pairs, and collections are groups of
documents. A Firestore database consists of a hierarchy of alternating collections
and documents, referred to by slash-separated paths like
"States/California/Cities/SanFrancisco".

This client is built around references to collections and documents. CollectionRefs
and DocumentRefs are lightweight values that refer to the corresponding database
entities. Creating a ref does not involve any network traffic.

[refs]

Reading

Use DocumentRef.Get to read a document. The result is a DocumentSnapshot.
Call its Data method to obtain the entire document contents as a map.

[docref.Get]

You can also obtain a single field with DataAt, or extract the data into a struct
with DataTo. With the type definition

[structDef]

we can extract the document's data into a value of type State:

[DataTo]

Note that this client supports struct tags beginning with "firestore:" that work like
the tags of the encoding/json package, letting you rename fields, ignore them, or
omit their values when empty.

To retrieve multiple documents from their references in a single call, use
Client.GetAll.

[GetAll]

Writing

For writing individual documents, use the methods on DocumentReference.
Create creates a new document.

[docref.Create]

The first return value is a WriteResult, which contains the time
at which the document was updated.

Create fails if the document exists. Another method, Set, either replaces an existing
document or creates a new one.

[docref.Set]

To update some fields of an existing document, use Update. It takes a list of
paths to update and their corresponding values.

[docref.Update]

Use DocumentRef.Delete to delete a document.

[docref.Delete]

Preconditions

You can condition Deletes or Updates on when a document was last changed. Specify
these preconditions as an option to a Delete or Update method. The check and the
write happen atomically with a single RPC.

[LUT-precond]

Here we update a doc only if it hasn't changed since we read it.
You could also do this with a transaction.

To perform multiple writes at once, use a WriteBatch. Its methods chain
for convenience.

WriteBatch.Commit sends the collected writes to the server, where they happen
atomically.

[WriteBatch]

Queries

You can use SQL to select documents from a collection. Begin with the collection, and
build up a query using Select, Where and other methods of Query.

[Query]

Call the Query's Documents method to get an iterator, and use it like
the other Google Cloud Client iterators.

[Documents]

To get all the documents in a collection, you can use the collection itself
as a query.

[CollQuery]

Transactions

Use a transaction to execute reads and writes atomically. All reads must happen
before any writes. Transaction creation, commit, rollback and retry are handled for
you by the Client.RunTransaction method; just provide a function and use the
read and write methods of the Transaction passed to it.

[Transaction]

Authentication

See examples of authorization and authentication at
https://godoc.org/cloud.google.com/go#pkg-examples.
*/
package firestore