Using KnockoutJS with SignalR in ASP.NET MVC

KnockoutJS is a MVVM implementation for JavaScript written by Steve Sanderson, in my opinion the author of the best ASP.NET MVC textbooks available. Simply put it lets you bind a JavaScript object model to your HTML UI using a Read more

A MongoDB Tutorial using C# and ASP.NET MVC

In this post I'm going to create a simple ASP.NET MVC website for a simple blog that uses MongoDB and the offical 10gen C# driver. MongoDB is no NOSQL database that stores information as Binary JSON (BSON) in documents. I Read more

Linq To SQL Tutorial

Check out some of my other Linq to SQL posts: EntityBase Inheritance Modifiers with SQLMetal Linq to SQL with WCF Services Linq to SQL Framework (Repository/Business wrapper) ObjectDataSource binding with server side paging and sorting Load Options Generic Framework using reflection This is a basic tutorial for Read more

Optimistic Concurrency with MongoDB C# driver and ASP.NET MVC – Prevent multiple users updating the same record

Posted on by Joe in ASP.NET, C#, MongoDB, MVC | Leave a comment

Over on my MongoDB C# Tutorial Richard asked how you would prevent multiple users from updating the same document. In this post I’m going to update the project in the tutorial to support this.

In my blog example this issue could occur when user 1 clicks to edit a post. While editing, user 2 also edits the same post. User 2 finishes their edit before user 1 and saves the post. User 1 continues editing and saves their changes. User 2’s changes are completely overwritten and neither user has any idea that it happened.

In this implementation, based on the above scenario I’m going to display an error to user 2 to tell them somebody else has updated to the post. They won’t be able to save their changes and it would be up to them to reload the post and make their changes again. Of course you could do something much more exciting, like show the two versions side by side and allow the user to merge the changes.

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MongoDB Sorting and Indexes

Posted on by Joe in MongoDB | Leave a comment

I’ve been looking at some of my MongoDB queries and trying to optimise them. I had one query that did a few ‘in’ statement and then sorted on a field called CreatedTime in descending order to give me the latest documents first.

My index looked something like:

{ “Field1” : 1, “Field2” : 1, “Field3” : 1, “CreatedTime” -1 }

With this index I got the following information from the Explain method:

“nscanned” : 8120, “nscannedObjects” : 4364, “n” : 121, “scanAndOrder” : true, “millis” : 62

I couldn’t really work out why it was scanning my entire index, and also half the documents in the collection. Playing around with the query I found that it was the sorting that was causing it. After removing my sort I get the following result:

“nscanned” : 128, “nscannedObjects” : 126, “n” : 121, “millis” : 2

Much better, although unfortunately in the incorrect order. If I was using a capped collection I could use reverse natural order, but I’m not. I thought that as I had CreatedTime indexed descending, doing a sort on that field descending would be fine, but just for fun I thought I’d put the field as the first field specified in my index to see if that would alter how MongoDB stores and uses the index:

{ “CreatedTime” -1, “Field1” : 1, “Field2” : 1, “Field3” : 1 }

Now running the query gives me the following:

“nscanned” : 256, “nscannedObjects” : 121, “n” : 121, “millis” : 2

That’s more like it, and you see the scanAndOrder attribute is no longer there. I’m limiting the query to 121 results, and the number of documents hit is 121, which is good as that means the query itself only used the index, and the exact documents were only accessed to get the fields I’m returning.

The query is scanning 256 index entries, presumably that how many it had to look at to match 121 documents based on my other query criteria.

A MongoDB Tutorial using C# and ASP.NET MVC

Posted on by Joe in ASP.NET, C#, MongoDB, MVC | 52 Comments

In this post I’m going to create a simple ASP.NET MVC website for a simple blog that uses MongoDB and the offical 10gen C# driver.

MongoDB is no NOSQL database that stores information as Binary JSON (BSON) in documents. I have been working with it now for around 6 months on an enterprise application and so far am loving it. Our application is currently in alpha phase but should be public early next year! If you are used to working with an RDBMS, it takes a little bit of getting used to as generally you work with a denormalized schema. This means thinking about things quite differently to how you would previously; you’re going to have repeating data which is a no-no in a relational database, but it’s going to give you awesome performance, sure you may need an offline process that runs nightly and goes and cleans up your data, but for the real time performance gains it’s worth it.

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Model Binding MongoDB ObjectId with ASP.NET MVC

Posted on by Joe in ASP.NET, C#, MongoDB, MVC | 12 Comments

If you’re using the MongoDB C# driver with ASP.NET MVC and have a property of type ObjectId in your model you will get the following error when trying to bind back to the model.

The parameter conversion from type ‘System.String’ to type ‘MongoDB.Bson.ObjectId’ failed because no type converter can convert between these types.

This can easily be resolved by creating a custom Model Binder which I’ll explain how to do in this article.

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MongoDB windows service won’t start

Posted on by Joe in MongoDB | Leave a comment

A couple of times now my MongoDB windows service won’t start after rebooting my machine. If you look at it in the services list it flicks between Starting and Started states but never really startsm and there doesn’t seem to be a way to get it to stop.

To fix this delete the mongod.lock file in your MongoDB data directory. It will immediately create a new one, but then the service will start.