Query Document using LINQ on Azure Cosmos DB

Do you prefer LINQ queries? I do because they provide a single consistent programming model across how they work with objects in application code and how they express query logic running in the database. In this article I will teach you how can you make LINQ queries as well as SQL queries to fetch documents from Cosmos DB.

Pre-requisite

If you have not yet setup your azure development environment then please read my below articles to start.

1. Get Free Sandbox Azure account for learning Azure
2. Creating Cosmos DB from DotNet Core Project
3. CRUD with Cosmos DB using Dotnet Core

How LINQ work in Cosmos DB

LINQ is a .Net Programming model that gives us an abstraction over querying data. Either you query XML or File or Object you always write a same program.

You can create an IQueryable object that directly queries Azure Cosmos DB, which translates the LINQ query into an Azure Cosmos DB query. The query is then passed to the Azure Cosmos DB server to retrieve a set of results in JSON format. The returned results are de-serialized into a stream of .NET objects on the client side.

Executing LINQ on Cosmos DB

Now we will fetch the user by their last name. This time I will write LINQ.

Using CreateDocumentQuery Method

CreateDocumentQuery will help us to run LINQ on cosmos DB. While querying we will enable the cross partition query.

private void ExecuteLinqQuery (string databaseName, string collectionName) {
    // Set some common query options
    FeedOptions queryOptions = new FeedOptions { MaxItemCount = -1, EnableCrossPartitionQuery = true };

    // Here we find nelapin via their LastName
    IQueryable<User> userQuery = this.client.CreateDocumentQuery<User> (
            UriFactory.CreateDocumentCollectionUri (databaseName, collectionName), queryOptions)
        .Where (u => u.LastName == "Pindakova");

    // The query is executed synchronously here, but can also be executed asynchronously via the IDocumentQuery<T> interface
    Console.WriteLine ("Running LINQ query...");
    foreach (User user in userQuery) {
        Console.WriteLine ("\tRead {0}",
            JsonConvert.SerializeObject (user, Formatting.Indented));
    }

    Console.WriteLine ("Press any key to continue ...");
    Console.ReadKey ();
}

Fetch User By LastName using LINQ Query

private async Task InitializeDB () {
    this.client = new DocumentClient (new Uri (ConfigurationManager.AppSettings["accountEndpoint"]), ConfigurationManager.AppSettings["accountKey"]);

    await this.client.CreateDatabaseIfNotExistsAsync (new Database { Id = "customers" });

    await this.client.CreateDocumentCollectionIfNotExistsAsync (UriFactory.CreateDatabaseUri ("customers"), new DocumentCollection {
        Id = "users", PartitionKey = new PartitionKeyDefinition () { Paths = new System.Collections.ObjectModel.Collection<string> () { "/userId" } }
    });

    Console.WriteLine ("Database and collection creation/validation is complete");

    // Create User
    await this.CreateUserDocumentIfNotExists ("customers", "users", new UserData ().nelapin);
    await this.CreateUserDocumentIfNotExists ("customers", "users", new UserData ().yanhe);

    // Read User
    await this.ReadUserDocument ("customers", "users", new UserData ().yanhe);

    // Update User
    var userToUpdate = new UserData ().yanhe;
    userToUpdate.LastName = "Ruk";
    await this.ReplaceUserDocument ("customers", "users", userToUpdate);

    // Delete User
    await this.DeleteUserDocument ("customers", "users", new UserData ().yanhe);

    👇 // Run LINQ
    this.ExecuteLinqQuery ("customers", "users");
}

Run dotnet run & notice we fetched the user. Source Code

Executing SQL Query on Cosmos DB

You may surprise that Cosmos DB also support running SQL querries to search an item. Let’s write code to select user by last name using SQL.

SELECT * FROM User WHERE User.lastName = 'Pindakova'"

Using CreateDocumentQuery Method

Let’s create new method where I will write SQL query to fetch user by his last name.

private void ExecuteSQLQuery (string databaseName, string collectionName) {
    // Set some common query options
    FeedOptions queryOptions = new FeedOptions { MaxItemCount = -1, EnableCrossPartitionQuery = true };

    /// Now execute the same query via direct SQL
    IQueryable<User> userQueryInSql = this.client.CreateDocumentQuery<User> (
        UriFactory.CreateDocumentCollectionUri (databaseName, collectionName),
        "SELECT * FROM User WHERE User.lastName = 'Pindakova'", queryOptions);

    Console.WriteLine ("Running direct SQL query...");
    foreach (User user in userQueryInSql) {
        Console.WriteLine ("\tRead {0}",
          JsonConvert.SerializeObject (user, Formatting.Indented));
    }

    Console.WriteLine ("Press any key to continue ...");
    Console.ReadKey ();
}

Fetch User By LastName using SQL Query

Lets call ExecuteSQLQuery from InitializeDB method.

private async Task InitializeDB () {
    this.client = new DocumentClient (new Uri (ConfigurationManager.AppSettings["accountEndpoint"]), ConfigurationManager.AppSettings["accountKey"]);

    await this.client.CreateDatabaseIfNotExistsAsync (new Database { Id = "customers" });

    await this.client.CreateDocumentCollectionIfNotExistsAsync (UriFactory.CreateDatabaseUri ("customers"), new DocumentCollection {
        Id = "users", PartitionKey = new PartitionKeyDefinition () { Paths = new System.Collections.ObjectModel.Collection<string> () { "/userId" } }
    });

    Console.WriteLine ("Database and collection creation/validation is complete");

    // Create User
    await this.CreateUserDocumentIfNotExists ("customers", "users", new UserData ().nelapin);
    await this.CreateUserDocumentIfNotExists ("customers", "users", new UserData ().yanhe);

    // Read User
    await this.ReadUserDocument ("customers", "users", new UserData ().yanhe);

    // Update User
    var userToUpdate = new UserData ().yanhe;
    userToUpdate.LastName = "Ruk";
    await this.ReplaceUserDocument ("customers", "users", userToUpdate);

    // Delete User
    await this.DeleteUserDocument ("customers", "users", new UserData ().yanhe);

    // Run LINQ
    this.ExecuteLinqQuery ("customers", "users");

    👇 // Run SQL
    this.ExecuteSQLQuery("customers", "users");
}

Next run dotnet run

Notice the output by running SQL query only. The console displays the output of the SQL queries.

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