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It's a MongoDB migration helper.

With this, you can write classes that implement steps to migrate a MongoDB database.

What do steps look like?

Like this:

public class AddAdminUser : IStep
    public async Task Execute(IMongoDatabase database)
        var users = database.GetCollection<BsonDocument>("users");

        var adminUser = new
            _id = Guid.NewGuid().ToString(),
            uid = "user1",
            claims = new[]
                new {type = ClaimTypes.Email, value = ""},
                new {type = ClaimTypes.Role, value = "admin"},

        await users.InsertOneAsync(adminUser.ToBsonDocument());

and then you execute it like this:

var migrator = new Migrator(
    connectionString: "mongodb://mongohost01/MyDatabase",
    steps: GetSteps.FromAssemblyOf<AddAdminUser>()


How to make robust steps

While steps are just C# code, and you can do anything you want in there to the passed-in IMongoDatabase, you are encouraged to write steps that do not change along with the rest of your code.

This means that you most likely want to use BsonDocument, magic strings, and anonymous types throughout.

Wouldn't want a rename of one of your C# classes to mess up how all of your existing migrations work.

Parallel execution

A distributed lock is used to coordinate execution, so Mongrow will never execute migrations concurrently.

How to number the steps

Steps are identified by a number and a "branch specification". The branch specification allows for co-existence of steps with the same number, thus escaping a global lock on the number sequence when working with multiple branches.

The branch specification defaults to master. You are encouraged to structure your steps like this:

| 1 - master |                 |
| 2 - master |                 |
| 3 - master | 3 - some-branch |
|            | 4 - some-branch |
| 5 - master |                 |

and so forth.

PLEASE NOTE: You are not allowed to INSERT a step into the sequence, so if step number n with any branch specification has been executed, you will get an exception if you add a migration with number < n for that branch specification.