{"id":12541,"date":"2022-10-01T02:23:00","date_gmt":"2022-09-30T20:53:00","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-what-is-a-combo-repository-and-a-service-bus\/"},"modified":"2022-10-01T02:23:00","modified_gmt":"2022-09-30T20:53:00","slug":"solved-what-is-a-combo-repository-and-a-service-bus","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-what-is-a-combo-repository-and-a-service-bus\/","title":{"rendered":"[Solved] What is a Combo Repository and a Service Bus?"},"content":{"rendered":"

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I am thinking about using a NoSQL database to scale database reads<\/p>\n<\/blockquote>\n

Good idea. It sounds like you are going down the path of Command Query Responsibility Segregation(CQRS)<\/a>. NoSql databases make for excellent read stores.<\/p>\n

The link<\/a> you referenced describes a technique to update
\nCombining SQL Server and MongoDB using NHibernate – this is what I meant by ‘Combo’ (combining) Repository. “Combo Repository” isn’t a standard pattern. Quoting the author:<\/p>\n

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Of course, theoretically, we could just move all the data to some NoSQL storage, but what if we don\u2019t want to get rid of our relational database completely? How can we combine<\/strong> them together?<\/p>\n<\/blockquote>\n

You’ve tagged your original question with both a Sql-Server<\/code> and a NoSql<\/code> database, so at a guess you’re in the Polyglot space<\/a><\/p>\n

The Repository Pattern<\/a> is a very common abstraction layer around data persistence.<\/p>\n

The “combining” link you’ve referenced specifically solves the problem of many-to-many relationships (often referred to as Junction tables in Sql), and the performance implications when there are many such relations.<\/p>\n

In the more general sense, as an alternative to providing interception points in NHibernate, you may \/ may not have abstracted data access via the repository pattern.<\/p>\n

Here’s an ultra simple (and non-generic) repository interface in C#:<\/p>\n

public interface IWidgetRepository\n{\n     Task<Widget> FetchWidget(string widgetKey);\n     Task SaveWidget(Widget toBeSaved);\n}   \n<\/code><\/pre>\n
Suppose we already have a SqlRepository:<\/p>\n
public class SqlWidgetRepository : IWidgetRepository\n{\n     public async Task<Widget> FetchWidget(string widgetKey)\n     {\n         ... Code to use Obtain an NHibernate session and retrieve and deserialize Widget\n     }\n    ... Other methods here\n}   \n<\/code><\/pre>\n
You could also choose to provide a MongoDb<\/code> implementation<\/p>\n
public class MongoWidgetRepository : IWidgetRepository\n{\n     public async Task<Widget> FetchWidget(string widgetKey)\n     {\n        ... Code to connect to a MongoDb secondary and Find() the \n           widget and deserialiaze into Widget\n     }\n    ... Other methods here\n}   \n<\/code><\/pre>\n
And to maintain both databases simultaneously, here’s an example of how this “combo” repository may look:<\/p>\n
public class ComboWidgetRepository : IWidgetRepository\n{\n     private readonly IWidgetRepository _repo1;\n     private readonly IWidgetRepository _repo2;\n\n     public ComboWidgetRepository(IWidgetRepository repo1, IWidgetRepository repo2)\n     {\n          repo1 = repo1;\n          repo1 = repo2;\n     }\n\n     public async Task<Widget> FetchWidget(string widgetKey)\n     {\n          \/\/ Just need the one ... first one wins\n          return await Task.WhenAny(repo1.FetchWidget(widgetKey), \n                                    repo2.FetchWidget(widgetKey));\n     }\n\n     public async Task SaveWidget(Widget toBeSaved)\n     {\n          \/\/ Need both to be saved\n          await Task.WhenAll(repo1.SaveWidget(toBeSaved), \n                             repo2.SaveWidget(toBeSaved));\n     }\n<\/code><\/pre>\n
The above “combo” repository may well fulfil the needs of a single system (and there are many other ways to keep two databases synchronized).<\/p>\n
CQRS is however frequently used at enterprise scale (i.e. where you have many systems, with many databases).<\/p>\n
My comment about an Enterprise Service Bus<\/a> will only make sense if you need to distribute data across an enterprise.<\/p>\n
The concept is simple<\/p>\n