Skip to main content

Data Model for Reporting over Windows Azure Tables (part 2)

Part 1
In the last post we talked a little about how we can calculate TOP 5 visited URLs per day for each user and TOP 5 visited URL anytime. For these cases I propose some ways on how we can store information on Windows Azure Table in a way that we can generate these reports.
In today post we will see how we can resolve the concurrence problem. We can have 10, 20 or 100 commands that want to execute over the same entity from Windows Azure Table. Because of this we need to guaranty that the writer has the last version of the entity before update it. If we will not be able to guaranty this… than our reporting solution will be compromised.
Windows Azure Table comes with a simple solution. Each entity that is stored on tables contains a unique key named ETag. ETag is changed every time when the entity is updated or changed. Based on this value we can know if we have the last version of an entity or the entity was changed from the moment when we receive it. ETag is the secret that give us support for concurrency access to Windows Azure Storage (Tables and Blobs).
Each entity that is retrieved from Windows Azure Tables has the ETag set. When someone will update any field from the given entity, the ETag value will be changed. In the moment when another user tries to make an update with an invalid ETag, the merge option feature will be used.
The data context contains a merge option filed that can be set manually. Based on this value, we can provide a custom behavior when a conflict appears. The values that are supported for MergeOption enum are:
  1. AppendOnly (default value)
  2. OverwriteChanges
  3. PreserveChanges
  4. NoTracking
For a description of this values please take a look here.
We saw that Windows Azure tables already have support for object “versioning” and automatic detecting and resolve merge conflict.
This can be used with success in our problem, when  in the case when the entity was update by another client we will need to retrieve the last version of the entity and update it.

Comments

Popular posts from this blog

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

Fundamental Books of a Software Engineer (version 2018)

More then six years ago I wrote a blog post about fundamental books that any software engineer (developer) should read. Now it is an excellent time to update this list with new entries.

There are 5 different categories of books, that represent the recommended path. For example, you start with Coding books, after that, you read books about Programming, Design and so on.
There are some books about C++ that I recommend not because you shall know C++, only because the concepts that you can learn from it.

Coding

Writing solid codeCode completeProgramming Pearls, more programming pearls(recommended)[NEW] Introduction to Algorithms

Programming

Refactoring (M. Fowler)Pragmatic ProgrammerClean code[NEW] Software Engineering: A Practitioner's Approach[NEW] The Mythical Man-Month[NEW] The Art of Computer Programming

Design

Applying UML and Patterns (GRASP patterns)C++ coding standards (Sutter, Alexandrescu)The C++ programming language (Stroustrup, Part IV)Object-oriented programming (Peter Coad)P…