pdevservices / dapper-wrapper

A simple abstraction atop the Dapper extension methods and TransactionScope for testability.

I am no longer maintaining this repository. If you have a fork or alternative for this library you think is good to direct people to, please let me know.

DapperWrapper is a library that wraps the Dapper extension methods on IDbConnection to make unit testing easier.

Why bother? Because stubbing the extension methods used in a method-under-unit-test is a pain in the ass. For instance, you can't just use a library like Moq to stub the .Query extension method on a fake IDbConnection. To work around this, I introduce a new abstraction, IDbExecutor.

The IDbExecutor Interface

The IDbExectuor interface has three methods, each corresponding to a Dapper extension method: Execute, Query, and Query<T>. Wherever you would previously inject an IDbConnection to use with Dapper, you instead inject an IDbExecutor. There is a single implementation of IDbExecutor included in DapperWrapper, SqlExecutor, that uses the Dapper extension methods against SqlConnection. Adding your own IDbExecutor against other implementations of IDbConnection is easy.

Example use of IDbExecutor:

public IEnumerable<SemanticVersion> GetAllPackageVersions(
  string packageId,
  IDbExecutor dbExecutor) {
  return dbExecutor.Query<string>("SELECT p.version FROM packages p WHERE p.id = @packageId", new { packageId })
    .Select(version => new SemanticVersion(version));
}

Injecting IDbExecutor

You probably already have an apporach to injecting IDbConnection into your app that you're happy with. That same approach will probably work just as well with IDbExecutor.

Personally, in my dependency container or service locator, I like to bind IDbExecutor to a method that instantiates a new SqlConnection and SqlExecutor. If you need to control the creation of the executor (for instance, you only need it conditionally), you could bind Func<IDbExecutor>. There's also an IDbExecutorFactory interface in DapperWrapper you could use, but it comes with the same downsides as any factory type.

Example of binding IDbExecutor and IDbExecutorFactory using Ninject:

public class DependenciesRegistrar : NinjectModule {
  public override void Load() {
    Bind<IDbExecutor>()
      .ToMethod(context => {
	    var sqlConnection = new SqlConnection(connectionString);
		sqlConnection.Open();
		return new SqlExecutor(sqlConnection);
      });
	Bind<IDbExecutorFactory>()
      .ToMethod(context => {
	    return new SqlExecutorFactory(connectionString);
      })
	  .InSingletonScope();
  }
}

Transactions

I sometimes need to assert whether a method-under-unit-test completes a transaction via TransactionScope. To make this easier, DapperWrapper also has an ITransactionScope interface (and TransactionScopeWrapper implementation) that makes it easy to create a fake transaction, and stub (and assert on) the Complete method. As with IDbExecutor, you can bind it directly, via Func<ITransactionScope>.