Using Cosmos DB databases

Setting up Cosmos DB options linked to Azure Cosmos DB Emulator

If you are testing Cosmos DB, then the Azure Cosmos DB Emulator is a great tool to use. It runs locally on the development system and allows you to test Cosmos DB queries without paying for a Cosmos DB database on Azure.

Here is an example of using the CreateUniqueClassCosmosDbEmulator<T> method, which takes the class as the name of the database.

public async Task TestAddCosmosBookWithReviewsOk()
{
    //SETUP
    var options = this.CreateUniqueClassCosmosDbEmulator<CosmosDbContext>();
    using var context = new CosmosDbContext(options);
    await context.Database.EnsureDeletedAsync();
    await context.Database.EnsureCreatedAsync();

    //ATTEMPT
    var cBook = new CosmosBook
    {
        CosmosBookId = 1,
        Title = "Book Title",
        PublishedDate = new DateTime(2019, 1,1),
    };
    context.Add(cBook);
    await context.SaveChangesAsync();

    //VERIFY
    await context.Books.FindAsync(1).ShouldNotBeNull();
}

Ability to add extra options to the DbContextOptionsBuilder<T>

All the previous extension methods have an optional parameter that allows you to set extra options at the DbContextOptionsBuilder<T> level. Below is part of the unit tests showing how to add/override options.

//... previous code removed to focus on the feature
var options = this.CreateUniqueClassCosmosDbEmulator<BookContext>(
    builder => builder.UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking)); //sets a tracking behavior
using (var context = new BookContext(options))
{
    //VERIFY
    var book = context.Books.First();
    context.Entry(book).State.ShouldEqual(EntityState.Detached);
}

The CreateUniqueMethodOptions() extension method

This returns a Cosmos DB options with the connection string from the appsettings.json file but the name of the database now has the type name of the object (which should be this) followed by the method name as a suffix. See test code below

[Fact]
public void TestSqlServerUniqueMethodOk()
{
    var options = this.CreateUniqueMethodCosmosDbEmulator<EfCoreContext>();
    using var context = new EfCoreContext(options))
    
    //... other parts left out   
}

NOTE: You shouldn't really need the CreateUniqueMethodOptions<T> method, as xUnit runs the methods inside a test class serially, so CreateUniqueClassOptions<T> should be enough to avoid parallel unit tests accessing the same database.

...WithLogTo

There are variations of these methods that include logging output - see Tools for capturing EF Core logging for more info.