EF Core: Manage Transactions Across Multiple DbContexts

Hey everyone! Ever found yourself wrestling with Entity Framework Core (EF Core) when you need to manage transactions that span multiple DbContext instances? It's a common scenario in complex applications, and getting it right is crucial for maintaining data integrity. In this article, we'll dive deep into how to handle transactions across multiple DbContext instances in EF Core, ensuring your data remains consistent and reliable.

Understanding the Challenge

Before we jump into the solutions, let's understand the problem. In a typical application, you might have multiple DbContext instances for different parts of your data model. For instance, one DbContext might manage user data, while another handles product information. When an operation requires changes across both databases, you need to ensure that either all changes are committed successfully, or none at all. This is where transactions come in.

Why can't we just use separate SaveChanges() calls? Well, each SaveChanges() call is an independent operation. If the first one succeeds but the second one fails, you're left with inconsistent data. Imagine updating a user's profile in one database and then failing to update their order history in another. That's a recipe for disaster! Transactions are designed to prevent exactly this kind of partial failure.

EF Core provides the IDbContextTransaction interface to manage transactions. However, using it with multiple DbContext instances requires a bit more work. You need to coordinate the transaction across all the involved contexts to ensure atomicity. Let's explore different approaches to achieve this.

Method 1: Using TransactionScope

The TransactionScope class in .NET provides a simple and elegant way to manage transactions. It automatically enlists all participating resources (like our DbContext instances) in a single transaction. Here's how you can use it:

using (var scope = new TransactionScope())
{
    using (var context1 = new Context1())
    {
        // Perform operations on context1
        context1.Database.EnsureCreated();
        context1.Entities.Add(new Entity { Name = "Entity 1" });
        context1.SaveChanges();
    }

    using (var context2 = new Context2())
    {
        // Perform operations on context2
        context2.Database.EnsureCreated();
        context2.Entities.Add(new Entity { Name = "Entity 2" });
        context2.SaveChanges();
    }

    scope.Complete();
}

In this example, we create a TransactionScope that encompasses operations on two different DbContext instances (Context1 and Context2). The scope.Complete() call at the end signals that the transaction should be committed. If an exception is thrown within the using block, the transaction is automatically rolled back, ensuring that no changes are persisted to the databases.

Pros of TransactionScope:

• Simplicity: It's easy to use and understand.
• Automatic enlistment: It automatically enlists resources in the transaction.
• Ambient transaction: It uses the ambient transaction, which means you don't need to explicitly pass the transaction to each DbContext.

Cons of TransactionScope:

• Requires MSDTC: It relies on the Microsoft Distributed Transaction Coordinator (MSDTC) when transactions span multiple databases, which can be a performance bottleneck and require additional configuration.
• Potential for escalation: If you're not careful, it can escalate to a distributed transaction, which can be slower and more resource-intensive.

Diving Deeper into TransactionScope

Let's elaborate on how TransactionScope works under the hood. When you create a TransactionScope, it creates an ambient transaction. This ambient transaction is associated with the current thread of execution. Any resource manager (like a DbContext) that supports transactions and is accessed within the scope of the TransactionScope automatically enlists in this transaction. When scope.Complete() is called, the transaction is marked for commit. If the scope is disposed without calling Complete(), the transaction is rolled back.

The reliance on MSDTC can be a significant consideration in production environments. MSDTC is a service that coordinates transactions across multiple databases or systems. It ensures that either all participating systems commit the transaction, or all roll it back. However, MSDTC can be complex to configure and manage, especially in distributed environments like cloud deployments. Ensure that MSDTC is properly configured on all servers involved in the transaction to avoid issues.

Moreover, the TransactionScope has different transaction scope options like TransactionScopeOption.Required, TransactionScopeOption.RequiresNew, and TransactionScopeOption.Suppress. Understanding these options is crucial to manage transaction behavior effectively, especially when dealing with nested transaction scopes or existing transactions.

Method 2: Using a Shared Connection and IDbContextTransaction

Another approach is to use a shared connection and manually manage the transaction using IDbContextTransaction. This method gives you more control over the transaction but also requires more code.

using (var connection = new SqlConnection(