With the Factory Pattern we provide a clean way to instantiate an object unknown to us at the time of implementation. The only thing we know is the interface of the object with a set of predefined properties and methods we need to use. More...

A DbSet in an Entity Framework DbContext has a Local property that let us access entities already retrieved within the scope of the DbContext. This way it is possible to further query a local entity set, without sending a query to the database. More...

The DbContext of Entity Framework lets us add, remove, attach and detach entities to and from it. Calling SaveChanges on the DbContext the Entity Framework performs different actions on entities dependant on their EntityState. So an added entity gets inserted, a removed entity gets deleted and so on. More...

Using a Timestamp column for optimistic concurrency control is quite a common practice in the SQL realm. While doing an insert, update or delete operation the database checks the Timestamp to see if the row has changed since the last time we retrieved it. More...

Entity Framework let us use the Code First Fluent API in the DbContext to configure how your entities are created. This is done by using the modelbuilder in an override of the OnModelCreate method as explained here. More...

Lets talk strategy for a moment. By default the entity framework uses a database creation strategy called CreateDatabaseIfNotExists. As the name implies this database initializer only creates the database if it’s not on your SQL Express or by a connectionstring specified location. More...

In the previous post we explored the use of the Entity Framework Code First Fluent API to configure properties and specify how the corresponding database is created. You can do this also by using data annotations. More...

Since Entity Framework 4.1 we can use the Code First Fluent API to specify how our database gets created, effectively overriding the default settings. This is also possible with data annotations, but the Fluent API gives us a way to keep this out of our POCO classes and into the data layer. More...

Many Brownfield Architectures (read this book!) provide a database with stored procedures for CUD operations. Or maybe the company we work for has a scary DBA believing his precious little handcrafted stored procedures are a piece of art. More...

To call and use stored procedures from a database in Entity Framework is pretty easy. Stored procedures can return Scalars, Entities and also Complex Types (properties aggregated) as we will see here.

In this example we add an existing stored procedure called sp_GetArtistNameAndCountryById. More...

And now for something completely different. Today I finished my first ever robot. She is a nice little color sorter. Now Ms. Color Sortress only likes to sort the color of the first ball she sees. Ones she got hold of all three of them, she falls asleep. More...

In Entity Framework, Table Per Hierarchy (TPT) mapping inheritance is a way to express closely related entities stored in a single table. We might store blue collar workers, middle managers and sales persons in a single Employee table, but represent them in our model as ‘distinct’ entities. More...

If you find yourself often in a situation where you query for a specific entity under the same conditions (e.g. whether a product list price is valid today), you might want to take a look at mapping conditions. More...

Another very flexible Entity Framework mapping feature, besides table splitting and entity splitting, is the use of complex type properties. These come into play when we want to group certain properties together to better mold and organize our model to our needs. More...

Besides Entity Framework entity splitting we can split a table into one or more entities. This is called table splitting. This is particularly handy when we use some table columns frequently while others in the same table less frequent. More...

There are a number of mapping scenarios in the Entity Framework to relate the data store to the conceptual model. If we have two tables with a key in common, one-to-one or zero-to-one relationship, we can merge them into one entity. More...

Using the Entity Framework as ORM, we can choose from three principles of creating the conceptual model (CSDL). We can either go from an existing database (Database First), create our model with POCO’s (Code First) or build our model from scratch in the designer (Model First). More...

We can intercept HTTP GET requests to WCF Data Services to add some custom business logic to an operation. We do this by decorating a method with a specific Query Interceptor attribute within the DataService derived class. More...

With WCF Data Services (formerly known as ADO.NET Data Services) we can publish any datasource with one or more IQueryable properties to the web. By using a with the Open Data Protocol (OData) formatted url we can query, update, insert and delete data from and to the database. More...

The Repository Pattern is a common construct to avoid duplication of data access logic throughout our application. This includes direct access to a database, ORM, WCF dataservices, xml files and so on. The sole purpose of the repository is to hide the nitty gritty details of accessing the data. More...

Each LINQ to SQL datacontext we instantiate holds its own identity map (based on Martin Fowlers Identity Map Pattern). This is basically a dictionary with identity keys pointing to entities in memory previously retrieved from the database – within the scope of the datacontext, that is. More...

Adding associated / related entities with LINQ to SQL is a breeze. In the snippet below we add a new TaskList with a new Task (‘Refactor’) for a specific Employee. LINQ to SQL keeps track of the associations and adds them as expected. More...

Quick snippet below as a reminder of the most basic CUD operations in LINQ to SQL. We insert new entities with InsertOnSubmit on the specific entity collection in the datacontext. We delete existing entities the same way with the use of DeleteOnSubmit. More...

We use a XML namespace to avoid name conflicts. With a namespace we can more specifically point to an element in a XML structure. In LINQ to XML a namespace is represented by the XNamespace class. In the code snippet below we simply add a fictive namespace to the list of cars we created in the previous example. More...

In the System.Xml.Linq namespace we find a lot of handy classes for creating and manipulating XML structures and files. XDocument respresents a complete XML structure with nodes (XNode) being elements (XElement) having attributes (XAttribute). More...

It’s sometimes not possible to use LINQ to query to a database or for some reason we want to execute a SQL query statement from within our code. That’s possible by using the DataContext ExecuteQuery or ExecuteCommand methods. More...

With LINQ to SQL we can get model inheritance with filtered mapping, called Single Table Inheritance. We do this by applying a discriminator value to the derived classes. By mapping this value LINQ to SQL knows to instantiate the appropriate base or derived class. More...

By default LINQ to SQL is lazy. It defers loading of data until the very first moment it is needed by your application. This behavior makes it possible to keep adding peaces to our query until we are ready to fire a SQL statement to the database. More...

The Chain of Responsibility pattern takes a request and flows through a chain of handlers. Each handler checks if it can handle the request according to some business rules. If the handler can’t handle the request it gets passed to the next handler in the chain. More...

The Command Pattern makes a execution request into an object. This makes it possible to store, search and transport requests and let clients call them via a common interface. This pattern is often used to implement undo or macro operations. More...

Lets build our own Inversion of Control container to do some dependency injection. Of course there is no need to IoC container with all the great frameworks like Unity, Castle Windsor or StructureMap. But it is fun and shows some of the inner workings of IoC container frameworks. More...

The last post in the SOLID by Example series deals with the Dependency Inversion Principle (DIP). It states that high-level classes should not depend on low-level classes. Both should depend on abstractions. Abstractions should not depend on details. More...

The fourth post in the SOLID by Example series deals with the Interface Segregation Principle (ISP). It states that clients should not be forced to implement interfaces they don’t use. Or as Uncle Bob puts it: Make fine grained interfaces that are client specific. More...

The third post in the SOLID by Example series deals with the Liskov Substitution Principle (LSP). It states that derived classes must be substitutable for their base classes. The principle was first mentioned by Barbara Liskov in the late eighties. More...

The second post in the SOLID by Example series deals with the Open / Closed Principle (OCP). This is the notion that an object should be open for extension, but closed for modification.

For us developers S.O.L.I.D.

More...

The first post in the SOLID by Example series deals with the Single Responsibility Principle (SRP). This is the notion that an object should have only a single responsibility. Uncle Bob defines a responsibility to be ‘a reason for change’. More...

The Strategy Pattern is a proven design construct to vary operations or algorithms independently from the clients that use it. The pattern underwrites the Open / Closed Principle of S.O.L.I.D., stating that a class should be open to extension, but closed to modification. More...

Threading operation calls within a single InstanceContext in WCF is configured by setting the ServiceBehavior attribute’s ConcurrencyMode property to one of the following enumeration values:

• Single Single threaded. subsequent calls are placed in a queue until the service lock is released.
More...

To prevent overloading of a service we can tune its performance by specifying how many calls can be made and how many sessions or instances can be created. We do this by configuring the ServiceThrottlingBehavior settings. We can also do this by configuring the serviceThrottling element in app.config. More...

In the previous example we wrapped a WCF service in a transaction scope by applying the Transaction Scope Required attribute. But what if we want to flow a transaction started from the client into the service and wrap the total round trip in a transaction? More...

An ACID transaction is the Atomic, Consistent, Isolated and Durable flow of work from one consistent state to another. For instance; If you draw money from an ATM you expect the same amount drawn of your bank account. More...

WCF sessions end on initiative of the client by calling close on the channel. In case of an error like network troubles or a client terminating, the time out settings of a service come into play. Both the client and the service can set the time out value. More...

Working every day with our favorite development environment, we sometimes forget the relative long history behind it. How did Visual Studio evolve over the years. Do you remember? Here’s a little reminder once made in celebration of the Visual Studio 2010 launch. More...

The instancing behavior of your WCF service is set with the InstanceContextMode property of the ServiceBehavior attribute. This configures the lifetime of a service managed by its instance context. There are three instance context modes, PerCall, PerSession and Single. More...

Hosting a WCF service in IIS keeps us bound to use HTTP based transport. As of IIS version 7 we can use the Windows Process Activation Service (WAS) to provide non-HTTP based transports like TCP for our services. More...

This example shows the easiest way of hosting and managing a WCF service in IIS version 5 and up. We use the example Transaction Service from a previous post to host in an IIS website.

First add a new webiste to you solution and choose WCF Service as a project type. More...

Hosting a WCF Service as a Managed Windows Service is pretty easy. Benefits of hosting it this way are automatic startup, built-in support to restart services on failure, choosing security identities for the service, manageability and maintainability. More...

Data Contracts used by a WCF service can change over time. To prevent anything from breaking we need some kind of data contract versioning. If strict schema validation is not necessary, we can implement the IExtensibleDataObject (IEDO) interface on our data contract to provide forward compatibility. More...

WCF Reliable Sessions, as defined by the WS-ReliableMessaging protocol, assures that SOAP messages don’t get lost, duplicated and/or re-ordered. It also prevents transport level errors (e.g. dropped connection). The reliability is at the SOAP message level, not at the transport level like TCP. More...

If you need much more reliable and durable messaging in WCF, Microsoft Message Queuing (MSMQ) comes into play. A message queue is a place where persistent messages are stored waiting to be delivered. A client or service can be down or busy but that doesn’t affect the other party. More...