Kot.MongoDB.Migrations

This package enables you to create and run MongoDb migrations. Simple and clean, with minimal dependencies. Supports wrapping migrations in a transaction. To use with DI containers, see Kot.MongoDB.Migrations.DI below.

Installation

Run the following command in the NuGet Package Manager Console:

PM> Install-Package Kot.MongoDB.Migrations

Usage

Creating migration classes

Create classes that describe your migrations. Each class must implement IMongoMigration. You can also derive from the MongoMigration class that provides a simple implementation.

class MyMigration : MongoMigration
{
    public MyMigration() : this("1.0.0") { }

    public override async Task UpAsync(IMongoDatabase db, IClientSessionHandle session, CancellationToken ct)
    {
        ...
    }

    public override async Task DownAsync(IMongoDatabase db, IClientSessionHandle session, CancellationToken ct)
    {
        ...
    }
}

Configuring migrator

Create an instance of IMigrator using MigratorBuilder (you can also create it manually, if you need). Provide a connection string or an instance of IMongoClient and MigrationOptions, then choose where to load migrations from.

var options = new MigrationOptions("myDb");
var migrator = MigratorBuilder.FromConnectionString("mongodb://localhost:27017", options)
    .LoadMigrationsFromCurrentDomain()
    .WithLogger(...) // Use this to pass ILoggerFactory if you want logs
    .Build();

Currently migrations can be loaded with the following methods:

• LoadMigrationsFromCurrentDomain() - load from current domain
• LoadMigrationsFromExecutingAssembly() - load from executing assembly
• LoadMigrationsFromAssembly(Assembly assembly) - load from a specified assembly
• LoadMigrationsFromNamespace(string @namespace) - load from a specified @namespace (scans all assemblies of current domain)
• LoadMigrations(IEnumerable migrations) - load from a specified migrations collection

Running migrations

To apply migrations, add the following code. This will check which migrations were applied before and determine which migrations should be applied now. You can also pass a target version as an argument in case you want to migrate (up/down) to a specific version.

MigrationResult result = await migrator.MigrateAsync();

Transactions

With the help of transactions you can ensure that a database stays in a consistent state when migration process fails. Make sure you know what can and what cannot be done with a database when using transactions (see official docs). To specify how to wrap migrations in transactions, set TransactionScope property of MigrationOptions. There are 3 options:

• None - transactions are not used (this is the default value)
• SingleMigration - each migration is wrapped in a separate transaction
• AllMigrations - all migrations a wrapped in a single transaction

Example:

var options = new MigrationOptions("myDb")
{
    TransactionScope = TransactionScope.SingleMigration
};

When one of the last two options is used, an instance of IClientSessionHandle is passed to the UpAsync and UpAsync methods of migrations. You should pass it to all DB operations like this:

public override async Task UpAsync(IMongoDatabase db, IClientSessionHandle session, CancellationToken cancellationToken)
{
    IMongoCollection<TestDoc> collection = db.GetCollection<TestDoc>("my_docs_collection");
    var doc = new TestDoc { SomeData = "Some data" };
    await collection.InsertOneAsync(session, doc, null, cancellationToken);
}

You can further configure transactions behavior by setting ClientSessionOptions property of MigrationOptions:

var options = new MigrationOptions("myDb")
{
    TransactionScope = TransactionScope.SingleMigration,
    ClientSessionOptions = new ClientSessionOptions
    {
        DefaultTransactionOptions = new TransactionOptions(maxCommitTime: TimeSpan.FromMinutes(1))
    }
};

Parallel runs

You might face situations with several parallel migration runs. E.g., if you migrate your DB on web app startup and there are several instances of the app. You can specify what to do in such cases by setting ParallelRunsBehavior property of MigrationOptions. There are 2 options:

• Cancel - silently cancel current run (this is the default value)
• Throw - throw an exception

Example:

var options = new MigrationOptions("myDb")
{
    ParallelRunsBehavior = ParallelRunsBehavior.Throw
}

Kot.MongoDB.Migrations.DI

This package enables you to use Kot.MongoDB.Migrations package with DI container.

Installation

Run the following command in the NuGet Package Manager Console:

PM> Install-Package Kot.MongoDB.Migrations.DI

Usage

Use extension method to register migration services. By default, migrations are loaded from current domain. You can configure this with different overloads of the extension method. It is also possible to pass an instance of IMongoClient instead of connection string or to not pass anything (in this case an instance of IMongoClient will be resolved from container).

var options = new MigrationOptions("myDb");
services.AddMongoMigrations("mongodb://localhost:27017", options, config => config.LoadMigrationsFromCurrentDomain());

Then resolve an instance of IMigrator and use as described above.