How to use Azure Table storage and Azure Cosmos DB for Table with C++

APPLIES TO: Table

This guide shows you common scenarios by using the Azure Table storage service or Azure Cosmos DB for Table. The samples are written in C++ and use the Azure Storage Client Library for C++. This article covers the following scenarios:

• Create and delete a table
• Work with table entities

Create accounts

Create an Azure service account

You can work with tables using the Azure Table storage or the Azure Cosmos DB. To learn more about the differences between table offerings in these two services, see the API for Table overview. You'll need to create an account for the service you're going to use. The following sections show how to create both Azure Table storage and the Azure Cosmos DB account, however you can just use one of them.

Create an Azure storage account

The easiest way to create an Azure storage account is by using the Azure portal. To learn more, see Create a storage account.

You can also create an Azure storage account by using Azure PowerShell or Azure CLI.

If you prefer not to create a storage account at this time, you can also use the Azure Storage Emulator to run and test your code in a local environment. For more information, see Use the Azure Storage Emulator for development and testing.

Create an Azure Cosmos DB for Table account

For instructions on creating an Azure Cosmos DB for Table account, see Create a database account.

Create a C++ application

In this guide, you use storage features from a C++ application. To do so, install the Azure Storage Client Library for C++.

To install the Azure Storage Client Library for C++, use the following methods:

• Linux: Follow the instructions given in the Azure Storage Client Library for C++ README: Getting Started on Linux page.
• Windows: On Windows, use vcpkg as the dependency manager. Follow the quick-start to initialize vcpkg. Then, use the following command to install the library:

.\vcpkg.exe install azure-storage-cpp

You can find a guide for how to build the source code and export to Nuget in the README file.

Configure access to the Table client library

To use the Azure storage APIs to access tables, add the following include statements to the top of the C++ file:

#include <was/storage_account.h>
#include <was/table.h>

An Azure Storage client or Azure Cosmos DB client uses a connection string to store endpoints and credentials to access data management services. When you run a client application, you must provide the storage connection string or Azure Cosmos DB connection string in the appropriate format.

Set up an Azure Storage connection string

This example shows how to declare a static field to hold the Azure Storage connection string:

// Define the Storage connection string with your values.
const utility::string_t storage_connection_string(U("DefaultEndpointsProtocol=https;AccountName=<your_storage_account>;AccountKey=<your_storage_account_key>"));

Use the name of your Storage account for <your_storage_account>. For <your_storage_account_key>, use the access key for the Storage account listed in the Azure portal. For information on Storage accounts and access keys, see Create a storage account.

Set up an Azure Cosmos DB connection string

This example shows how to declare a static field to hold the Azure Cosmos DB connection string:

// Define the Azure Cosmos DB connection string with your values.
const utility::string_t storage_connection_string(U("DefaultEndpointsProtocol=https;AccountName=<your_cosmos_db_account>;AccountKey=<your_cosmos_db_account_key>;TableEndpoint=<your_cosmos_db_endpoint>"));

Use the name of your Azure Cosmos DB account for <your_cosmos_db_account>. Enter your primary key for <your_cosmos_db_account_key>. Enter the endpoint listed in the Azure portal for <your_cosmos_db_endpoint>.

To test your application in your local Windows-based computer, you can use the Azure Storage Emulator that is installed with the Azure SDK. The Storage Emulator is a utility that simulates the Azure Blob, Queue, and Table services available on your local development machine. The following example shows how to declare a static field to hold the connection string to your local storage emulator:

// Define the connection string with Azure Storage Emulator.
const utility::string_t storage_connection_string(U("UseDevelopmentStorage=true;"));  

To start the Azure Storage Emulator, from your Windows desktop, select the Start button or the Windows key. Enter and run Azure Storage Emulator. For more information, see Use the Azure Storage Emulator for development and testing.

Retrieve your connection string

You can use the cloud_storage_account class to represent your storage account information. To retrieve your storage account information from the storage connection string, use the parse method.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

Next, get a reference to a cloud_table_client class. This class lets you get reference objects for tables and entities stored within the Table storage service. The following code creates a cloud_table_client object by using the storage account object you retrieved previously:

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

Create and add entities to a table

Create a table

A cloud_table_client object lets you get reference objects for tables and entities. The following code creates a cloud_table_client object and uses it to create a new table.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);  

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Retrieve a reference to a table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Create the table if it doesn't exist.
table.create_if_not_exists();  

Add an entity to a table

To add an entity to a table, create a new table_entity object and pass it to table_operation::insert_entity. The following code uses the customer's first name as the row key and last name as the partition key. Together, an entity's partition and row key uniquely identify the entity in the table. Entities with the same partition key can be queried faster than entities with different partition keys. Using diverse partition keys allows for greater parallel operation scalability. For more information, see Azure storage performance and scalability checklist.

The following code creates a new instance of table_entity with some customer data to store. The code next calls table_operation::insert_entity to create a table_operation object to insert an entity into a table, and associates the new table entity with it. Finally, the code calls the execute method on the cloud_table object. The new table_operation sends a request to the Table service to insert the new customer entity into the people table.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Retrieve a reference to a table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Create the table if it doesn't exist.
table.create_if_not_exists();

// Create a new customer entity.
azure::storage::table_entity customer1(U("Harp"), U("Walter"));

azure::storage::table_entity::properties_type& properties = customer1.properties();
properties.reserve(2);
properties[U("Email")] = azure::storage::entity_property(U("Walter@contoso.com"));

properties[U("Phone")] = azure::storage::entity_property(U("425-555-0101"));

// Create the table operation that inserts the customer entity.
azure::storage::table_operation insert_operation = azure::storage::table_operation::insert_entity(customer1);

// Execute the insert operation.
azure::storage::table_result insert_result = table.execute(insert_operation);

Insert a batch of entities

You can insert a batch of entities to the Table service in one write operation. The following code creates a table_batch_operation object, and then adds three insert operations to it. Each insert operation is added by creating a new entity object, setting its values, and then calling the insert method on the table_batch_operation object to associate the entity with a new insert operation. Then, the code calls cloud_table.execute to run the operation.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Define a batch operation.
azure::storage::table_batch_operation batch_operation;

// Create a customer entity and add it to the table.
azure::storage::table_entity customer1(U("Smith"), U("Jeff"));

azure::storage::table_entity::properties_type& properties1 = customer1.properties();
properties1.reserve(2);
properties1[U("Email")] = azure::storage::entity_property(U("Jeff@contoso.com"));
properties1[U("Phone")] = azure::storage::entity_property(U("425-555-0104"));

// Create another customer entity and add it to the table.
azure::storage::table_entity customer2(U("Smith"), U("Ben"));

azure::storage::table_entity::properties_type& properties2 = customer2.properties();
properties2.reserve(2);
properties2[U("Email")] = azure::storage::entity_property(U("Ben@contoso.com"));
properties2[U("Phone")] = azure::storage::entity_property(U("425-555-0102"));

// Create a third customer entity to add to the table.
azure::storage::table_entity customer3(U("Smith"), U("Denise"));

azure::storage::table_entity::properties_type& properties3 = customer3.properties();
properties3.reserve(2);
properties3[U("Email")] = azure::storage::entity_property(U("Denise@contoso.com"));
properties3[U("Phone")] = azure::storage::entity_property(U("425-555-0103"));

// Add customer entities to the batch insert operation.
batch_operation.insert_or_replace_entity(customer1);
batch_operation.insert_or_replace_entity(customer2);
batch_operation.insert_or_replace_entity(customer3);

// Execute the batch operation.
std::vector<azure::storage::table_result> results = table.execute_batch(batch_operation);

Some things to note on batch operations:

• You can do up to 100 insert, delete, merge, replace, insert-or-merge, and insert-or-replace operations in any combination in a single batch.
• A batch operation can have a retrieve operation, if it's the only operation in the batch.
• All entities in a single batch operation must have the same partition key.
• A batch operation is limited to a 4-MB data payload.

Query and modify entities

Retrieve all entities in a partition

To query a table for all entities in a partition, use a table_query object. The following code example specifies a filter for entities where Smith is the partition key. This example prints the fields of each entity in the query results to the console.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Construct the query operation for all customer entities where PartitionKey="Smith".
azure::storage::table_query query;

query.set_filter_string(azure::storage::table_query::generate_filter_condition(U("PartitionKey"), azure::storage::query_comparison_operator::equal, U("Smith")));

// Execute the query.
azure::storage::table_query_iterator it = table.execute_query(query);

// Print the fields for each customer.
azure::storage::table_query_iterator end_of_results;
for (; it != end_of_results; ++it)
{
    const azure::storage::table_entity::properties_type& properties = it->properties();

    std::wcout << U("PartitionKey: ") << it->partition_key() << U(", RowKey: ") << it->row_key()
        << U(", Property1: ") << properties.at(U("Email")).string_value()
        << U(", Property2: ") << properties.at(U("Phone")).string_value() << std::endl;
}  

The query in this example returns all the entities that match the filter criteria. If you have large tables and need to download the table entities often, we recommend that you store your data in Azure storage blobs instead.

Retrieve a range of entities in a partition

If you don't want to query all the entities in a partition, you can specify a range. Combine the partition key filter with a row key filter. The following code example uses two filters to get all entities in partition Smith where the row key (first name) starts with a letter earlier than E in the alphabet, and then prints the query results.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Create the table query.
azure::storage::table_query query;

query.set_filter_string(azure::storage::table_query::combine_filter_conditions(
    azure::storage::table_query::generate_filter_condition(U("PartitionKey"),
    azure::storage::query_comparison_operator::equal, U("Smith")),
    azure::storage::query_logical_operator::op_and,
    azure::storage::table_query::generate_filter_condition(U("RowKey"), azure::storage::query_comparison_operator::less_than, U("E"))));

// Execute the query.
azure::storage::table_query_iterator it = table.execute_query(query);

// Loop through the results, displaying information about the entity.
azure::storage::table_query_iterator end_of_results;
for (; it != end_of_results; ++it)
{
    const azure::storage::table_entity::properties_type& properties = it->properties();

    std::wcout << U("PartitionKey: ") << it->partition_key() << U(", RowKey: ") << it->row_key()
        << U(", Property1: ") << properties.at(U("Email")).string_value()
        << U(", Property2: ") << properties.at(U("Phone")).string_value() << std::endl;
}  

Retrieve a single entity

You can write a query to retrieve a single, specific entity. The following code uses table_operation::retrieve_entity to specify the customer Jeff Smith. This method returns just one entity, rather than a collection, and the returned value is in table_result. Specifying both partition and row keys in a query is the fastest way to retrieve a single entity from the Table service.

azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Retrieve the entity with partition key of "Smith" and row key of "Jeff".
azure::storage::table_operation retrieve_operation = azure::storage::table_operation::retrieve_entity(U("Smith"), U("Jeff"));
azure::storage::table_result retrieve_result = table.execute(retrieve_operation);

// Output the entity.
azure::storage::table_entity entity = retrieve_result.entity();
const azure::storage::table_entity::properties_type& properties = entity.properties();

std::wcout << U("PartitionKey: ") << entity.partition_key() << U(", RowKey: ") << entity.row_key()
    << U(", Property1: ") << properties.at(U("Email")).string_value()
    << U(", Property2: ") << properties.at(U("Phone")).string_value() << std::endl;

Replace an entity

To replace an entity, retrieve it from the Table service, modify the entity object, and then save the changes back to the Table service. The following code changes an existing customer's phone number and email address. Instead of calling table_operation::insert_entity, this code uses table_operation::replace_entity. This approach causes the entity to be fully replaced on the server, unless the entity on the server has changed since it was retrieved. If it has been changed, the operation fails. This failure prevents your application from overwriting a change made between the retrieval and update by another component. The proper handling of this failure is to retrieve the entity again, make your changes, if still valid, and then do another table_operation::replace_entity operation.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Replace an entity.
azure::storage::table_entity entity_to_replace(U("Smith"), U("Jeff"));
azure::storage::table_entity::properties_type& properties_to_replace = entity_to_replace.properties();
properties_to_replace.reserve(2);

// Specify a new phone number.
properties_to_replace[U("Phone")] = azure::storage::entity_property(U("425-555-0106"));

// Specify a new email address.
properties_to_replace[U("Email")] = azure::storage::entity_property(U("JeffS@contoso.com"));

// Create an operation to replace the entity.
azure::storage::table_operation replace_operation = azure::storage::table_operation::replace_entity(entity_to_replace);

// Submit the operation to the Table service.
azure::storage::table_result replace_result = table.execute(replace_operation);

Insert or replace an entity

table_operation::replace_entity operations fail if the entity has been changed since it was retrieved from the server. Furthermore, you must retrieve the entity from the server first in order for table_operation::replace_entity to be successful. Sometimes, you don't know if the entity exists on the server. The current values stored in it are irrelevant, because your update should overwrite them all. To accomplish this result, use a table_operation::insert_or_replace_entity operation. This operation inserts the entity if it doesn't exist. The operation replaces the entity if it exists. In the following code example, the customer entity for Jeff Smith is still retrieved, but it's then saved back to the server by using table_operation::insert_or_replace_entity. Any updates made to the entity between the retrieval and update operation will be overwritten.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Insert or replace an entity.
azure::storage::table_entity entity_to_insert_or_replace(U("Smith"), U("Jeff"));
azure::storage::table_entity::properties_type& properties_to_insert_or_replace = entity_to_insert_or_replace.properties();

properties_to_insert_or_replace.reserve(2);

// Specify a phone number.
properties_to_insert_or_replace[U("Phone")] = azure::storage::entity_property(U("425-555-0107"));

// Specify an email address.
properties_to_insert_or_replace[U("Email")] = azure::storage::entity_property(U("Jeffsm@contoso.com"));

// Create an operation to insert or replace the entity.
azure::storage::table_operation insert_or_replace_operation = azure::storage::table_operation::insert_or_replace_entity(entity_to_insert_or_replace);

// Submit the operation to the Table service.
azure::storage::table_result insert_or_replace_result = table.execute(insert_or_replace_operation);

Query a subset of entity properties

A query to a table can retrieve just a few properties from an entity. The query in the following code uses the table_query::set_select_columns method to return only the email addresses of entities in the table.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Define the query, and select only the Email property.
azure::storage::table_query query;
std::vector<utility::string_t> columns;

columns.push_back(U("Email"));
query.set_select_columns(columns);

// Execute the query.
azure::storage::table_query_iterator it = table.execute_query(query);

// Display the results.
azure::storage::table_query_iterator end_of_results;
for (; it != end_of_results; ++it)
{
    std::wcout << U("PartitionKey: ") << it->partition_key() << U(", RowKey: ") << it->row_key();

    const azure::storage::table_entity::properties_type& properties = it->properties();
    for (auto prop_it = properties.begin(); prop_it != properties.end(); ++prop_it)
    {
        std::wcout << ", " << prop_it->first << ": " << prop_it->second.str();
    }

    std::wcout << std::endl;
}

Delete content

Delete an entity

You can delete an entity after you retrieve it. After you retrieve an entity, call table_operation::delete_entity with the entity to delete. Then call the cloud_table.execute method. The following code retrieves and deletes an entity with a partition key of Smith and a row key of Jeff.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Create an operation to retrieve the entity with partition key of "Smith" and row key of "Jeff".
azure::storage::table_operation retrieve_operation = azure::storage::table_operation::retrieve_entity(U("Smith"), U("Jeff"));
azure::storage::table_result retrieve_result = table.execute(retrieve_operation);

// Create an operation to delete the entity.
azure::storage::table_operation delete_operation = azure::storage::table_operation::delete_entity(retrieve_result.entity());

// Submit the delete operation to the Table service.
azure::storage::table_result delete_result = table.execute(delete_operation);  

Delete a table

Finally, the following code example deletes a table from a storage account. A table that has been deleted is unavailable to be re-created for some time following the deletion.

// Retrieve the storage account from the connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);

// Create the table client.
azure::storage::cloud_table_client table_client = storage_account.create_cloud_table_client();

// Create a cloud table object for the table.
azure::storage::cloud_table table = table_client.get_table_reference(U("people"));

// Delete the table if it exists
if (table.delete_table_if_exists())
{
    std::cout << "Table deleted!";
}
else
{
    std::cout << "Table didn't exist";
}

Troubleshooting

For Visual Studio Community Edition, if your project gets build errors because of the include files storage_account.h and table.h, remove the /permissive- compiler switch:

1. In Solution Explorer, right-click your project and select Properties.
2. In the Property Pages dialog box, expand Configuration Properties, expand C/C++, and select Language.
3. Set Conformance mode to No.

Next steps

Azure Storage Explorer is a free, standalone app from Microsoft that enables you to work visually with Azure Storage data on Windows, macOS, and Linux.

Follow these links to learn more about Azure Storage and the API for Table in Azure Cosmos DB:

• Introduction to the API for Table
• List Azure Storage resources in C++
• Storage Client Library for C++ reference
• Azure Storage documentation