Tutorial: Query data from a API for Cassandra account in Azure Cosmos DB

Članek
08/14/2024

APPLIES TO: Cassandra

As a developer, you might have applications that use key/value pairs. You can use a API for Cassandra account in Azure Cosmos DB to store and query the key/value data. This tutorial shows how to query user data from a API for Cassandra account in Azure Cosmos DB by using a Java application. The Java application uses the Java driver and queries user data such as user ID, user name, and user city.

This tutorial covers the following tasks:

Query data from a Cassandra table
Run the app

If you don’t have an Azure subscription, create a free account before you begin.

Prerequisites

This article belongs to a multi-part tutorial. Before you start, make sure to complete the previous steps to create the API for Cassandra account, keyspace, table, and load sample data into the table.

Query data

Use the following steps to query data from your API for Cassandra account:

Open the UserRepository.java file under the folder src\main\java\com\azure\cosmosdb\cassandra. Append the following code block. This code provides three methods:

To query all users in the database
To query a specific user filtered by user ID
To delete a table

/**
* Select all rows from user table
*/
public void selectAllUsers() {

  final String query = "SELECT * FROM uprofile.user";
  List<Row> rows = session.execute(query).all();

  for (Row row : rows) {
     LOGGER.info("Obtained row: {} | {} | {} ", row.getInt("user_id"), row.getString("user_name"), row.getString("user_bcity"));
  }
}

/**
* Select a row from user table
*
* @param id user_id
*/
public void selectUser(int id) {
   final String query = "SELECT * FROM uprofile.user where user_id = 3";
   Row row = session.execute(query).one();

   LOGGER.info("Obtained row: {} | {} | {} ", row.getInt("user_id"), row.getString("user_name"), row.getString("user_bcity"));
}

/**
* Delete user table.
*/
public void deleteTable() {
  final String query = "DROP TABLE IF EXISTS uprofile.user";
  session.execute(query);
}

Open the UserProfile.java file under the folder src\main\java\com\azure\cosmosdb\cassandra. This class contains the main method that calls the createKeyspace and createTable, insert data methods you defined earlier. Now append the following code that queries all users or a specific user:
```
LOGGER.info("Select all users");
repository.selectAllUsers();

LOGGER.info("Select a user by id (3)");
repository.selectUser(3);

LOGGER.info("Delete the users profile table");
repository.deleteTable();
```

Run the Java app

Open a command prompt or terminal window. Paste the following code block.

This code changes the directory (cd) to the folder path where you created the project. Then, it runs the mvn clean install command to generate the cosmosdb-cassandra-examples.jar file within the target folder. Finally, it runs the Java application.
```
cd "cassandra-demo"

mvn clean install

java -cp target/cosmosdb-cassandra-examples.jar com.azure.cosmosdb.cassandra.examples.UserProfile
```
Now, in the Azure portal, open the Data Explorer and confirm that the user table is deleted.

Clean up resources

When they're no longer needed, you can delete the resource group, Azure Cosmos DB account, and all the related resources. To do so, select the resource group for the virtual machine, select Delete, and then confirm the name of the resource group to delete.

Next steps

In this tutorial, you've learned how to query data from a API for Cassandra account in Azure Cosmos DB. You can now proceed to the next article:

Migrate data to API for Cassandra account

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