main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
	"github.com/Azure/azure-sdk-for-go/sdk/data/azcosmos"
)

func main() {
	// InitializeDatabaseAndContainer() provides the convenience to quickly set up a cosmos DB and its container for our demonstration.
	// Comment out InitializeDatabaseAndContainer() and only run demo() if the DB and container have been deployed on the cloud.

	InitializeDatabaseAndContainer()

	demoCrudAndEtag()
}

func demoCrudAndEtag() {
	book := sampleBook

	addBookInfo(book) // Add an item into the container

	receivedBook1, etag1 := readBookInfo(book)
	updateBookPrice(receivedBook1, 120.00, etag1) // This will succeed
	updateBookPrice(receivedBook1, 150.00, etag1) // This is to mock a concurrent Write operation. It will be rejected, since a new Etag has been generated by the previous update operation.
	receivedBook2, etag2 := readBookInfo(book)
	updateBookPrice(receivedBook2, 150.00, etag2) // This will succeed since etag2 is the latest ETag so far.

	demoSqlQuery(book)

	deleteBookInfo(receivedBook2, etag2)       // This will be rejected for outdated ETag as well.
	receivedBook3, etag3 := readBookInfo(book) // receivedBook3 will contain the updated price 150.00
	deleteBookInfo(receivedBook3, etag3)       // This will succeed since etag3 is the latest ETag.
}

func addBookInfo(book Book) {
	fmt.Printf("\r\nAdding sample book entry to DB...\r\n")
	container := GetContainer()

	pk := azcosmos.NewPartitionKeyString(book.Title)

	marshalled, err := json.Marshal(book)
	if err != nil {
		panic(err)
	}

	itemResponse, err := container.CreateItem(context.Background(), pk, marshalled, nil)
	if err != nil {
		panic(err)
	}

	fmt.Printf("Sample book entry added. ActivityId %s consuming %v RU\r\n", itemResponse.ActivityID, itemResponse.RequestCharge)
}

func readBookInfo(book Book) (Book, azcore.ETag) {
	fmt.Printf("\r\nReading book info...\r\n")
	container := GetContainer()
	pk := azcosmos.NewPartitionKeyString(book.Title)
	itemResponse, err := container.ReadItem(context.Background(), pk, book.Id, nil)

	var receivedBook Book
	err = json.Unmarshal(itemResponse.Value, &receivedBook)
	if err != nil {
		panic(err)
	}

	jsonStr, err := json.Marshal(receivedBook)
	if err != nil {
		fmt.Printf("Error: %s", err.Error())
	}

	fmt.Printf("Book info read=%s\r\nEtag=%s\r\nActivityId %s consuming %v RU\r\n", string(jsonStr), itemResponse.ETag, itemResponse.ActivityID, itemResponse.RequestCharge)
	return receivedBook, itemResponse.ETag
}

func updateBookPrice(book Book, newPrice float32, etag azcore.ETag) {
	fmt.Printf("\r\nUpdating book price...\r\n")
	container := GetContainer()
	book.Price = newPrice
	marshalledBook, err := json.Marshal(book)
	if err != nil {
		panic(err)
	}

	// Replace with Etag
	pk := azcosmos.NewPartitionKeyString(book.Title)
	itemResponse, err := container.ReplaceItem(context.Background(), pk, book.Id, marshalledBook, &azcosmos.ItemOptions{IfMatchEtag: &etag})
	if err != nil {
		fmt.Printf("Update rejected.\r\nError is\r\n%s\r\n", err)

	} else {
		fmt.Printf("Book price updated.\r\nEtag=%s\r\nActivityId %s consuming %v RU\r\n", itemResponse.ETag, itemResponse.ActivityID, itemResponse.RequestCharge)
	}
}

func deleteBookInfo(book Book, etag azcore.ETag) {
	fmt.Printf("\r\nDeleting book info...\r\n")
	container := GetContainer()

	// Replace with Etag
	pk := azcosmos.NewPartitionKeyString(book.Title)
	itemResponse, err := container.DeleteItem(context.Background(), pk, book.Id, &azcosmos.ItemOptions{IfMatchEtag: &etag})
	if err != nil {
		fmt.Printf("Delete operation rejected.\r\nError is\r\n%s\r\n", err)

	} else {
		fmt.Printf("Book info deleted.\r\nActivityId %s consuming %v RU\r\n", itemResponse.ActivityID, itemResponse.RequestCharge)
	}
}

func demoSqlQuery(book Book) {
	fmt.Printf("\r\nQuerying book info...\r\n")
	container := GetContainer()
	pager := container.NewQueryItemsPager("select * from books b", azcosmos.NewPartitionKeyString(book.Title), nil)
	for pager.More() {
		queryResponse, err := pager.NextPage(context.Background())
		fmt.Printf("Reponse = %s\r\n", queryResponse.RawResponse.Body)
		if err != nil {
			fmt.Printf("failed to get next page of query response. error = %s\r\n", err)
		}
		for _, item := range queryResponse.Items {
			fmt.Printf("Book = %s\r\n", string(item))
		}
	}
}