In our example application, we just select the authors table, keep the suggested Model Namespace and click on “Finish” (see screenshot below).
Note: During the automated generation of the EDM, the mappings are automatically constructed for the selected tables and Views.
Step 4 – The Entity Data Model Designer
The following screen shows the graphical tool (EDM Designer) within Visual Studio 2008 that is used for visually modifying the generated Entity Data Model. As you can see on the screenshot, I noted three main “components/concepts”. These are: (i) Entity
, (ii) Mapping Tool
, and (iii) Model Browser
At this point it is of great importance to explain the above three components. So we can see that on the workspace there is an Entity
named authors. So what is an Entity in plain words
? As you might have assumed is a representation of the “authors” table which exists in the “Pubs” database. Well that is correct but there is one word missing; conceptual
. It is a conceptual representation of the “authors” table in the “Pubs” database. Also, in its simple form, an entity contains scalar properties.
In the Mapping Tool’s
view, you can see that the “authors” entity is mapped
to the “authors” database. So, on the left you see the table/columns of the relational model (Database) and on the right (after the operator) you can see the scalar properties of the entity that are mapped to the corresponding columns of the table on which the “authors” entity is also mapped.
I hope you didn't get confused but if you did don't worry, there is more explanation following. :)
Let’s have a closer look on the above concepts with the following screenshot:
Let’s see the exact mappings for this example:
- We have the “authors” entity mapped to the ”authors” table
- We also have the displayed pairs of the table columns/data types mapped to pairs of the entity’s scalar properties/data types
So, when you query your Entity Data Model and ask for the value of the au_id scalar property within the Authors Entity, the Entity Framework will know through the mappings that it must query for the au_id column in the authors table in the Pubs database.
At this point, someone might still ask: what exactly is the “authors” entity and by what means is “conceptual”?
Let’s proceed to the next screenshot which will help better understand what exactly this EDM is and how exactly you can modify it with the graphical tool.
If you compare the above screenshot with the previous one, you will notice that some things changed. The entity formerly called Authors
is now called DemoAuthors
. Also the scalar properties au_id
are now called id
Well, this is not a problem at all and that is one of the strong points about ADO .NET Entity Framework; you can modify the conceptual schema in the way you want, use among other naming conventions you might prefer, add new entities, use inheritance and entity splitting (these will be explained in subsequent demos) and much more without causing any problems to the Data Access.
The only thing that you must have in mind is that the mappings should always be maintained. In the above example, even though we have changed the name of the entity and some of its scalar properties, the mappings were automatically updated! Well, in some cases where you might perform some really complex modifications, you might have to fine-tune the mappings manually, though after all, I don’t think that this would be a problem. :)
So, based on the last few screenshots, we talked about the EDM graphical tool workspace (that is the place where entities are displayed) and about the mapping tool and mapping details.
The third component of the graphical tool is the Model Browser. In the Model Browser you can see all your objects used by EDM. To this end, you can see: Entities-Entity Types, Associations – Association Sets (representing the relationships between entities) and Function Imports (can be used for mapping database stored procedures and UDTs to the EDM). Also, you can see the corresponding database objects that are being used (mapped to the EDM) such as: Tables/Views, Constraints (for setting up relationships between database tables) and Stored Procedures respectively. By right-clicking on the model browser or on the EDM workspace, you can also update the model by adding and then mapping, even more database objects. Additionally, in the same way, you can refresh the model meaning that it will “read” again the database for possible changes.
Okay, at this point I believe that we can save our simple model, build our project and continue!Step 5 – Use the EDM for Data Access
By now we have created the EDM, and we now need to use it as a data source.To this end, let’s add a new data source to the project and select the type Object as illustrated in the following screenshot:
Then, we just have to select the object we want to bind to the data source we are creating. At this point select the DemoAuthors
entity and click on Next:
That’s it! Click on Finish and voila, you have the data source ready to serve data via the EDM!
Let’s continue by dragging and dropping the DemoAuthors data source onto the form as in the following screenshot (if Data Sources explorer is not visible, you can change this setting from the View menu item):
After dragging and dropping the DemoAuthors data source on the form we end up to the following screen:
By the way, let’s modify the properties of the Save
icon and set Enabled
(we need to add an event to this button/icon for allowing us to be able to post any changes performed on the data during the runtime/testing phase).
Then press F7. It is time to write some code!!! :)
The two red rectangles contain the code that you should add:
In the first rectangle, we just declare an EDM object (based on the Entity connection string we saw earlier).
In the second rectangle, after the form’s initialization, we instantiate the EDM object called model (notice the pubsEntities
object used here; that’s the connection string to our EDM). We also set the data source for the datagridview. How about the way we reference our data? Quite simple, right?
Let’s also add some more code by going back to the form, double-clicking on the Save
icon, and adding code as in the following screenshot:
The only piece of code you need to add in order to be executed whenever the Save
icon is clicked, is a single line: model.SaveChanges();
And now the last step; build the project and run it.
That’s it! Congratulations, you have just built your first ADO .NET Entity Framework C# Application!
When the application starts, data is retrieved from the database via the EDM and displayed on the datagridview just like in the following screenshot:
Also, when you modify a record and click on the Save
icon, the underlying event handler code (model.SaveChanges()
method call) will post the changes to the Pubs database in SQL Server via the EDM. All the changes are saved with just the invocation of a single method! Concepts demonstrated
As a recap, let’s summarize the concepts presented in this tutorial. Among other, we performed and examined the following:
If I have forgotten anything, you are welcome to drop me a comment! :)
- What actually is the ADO .NET Entity Framework (EF)
- What is the Entity Data Model (EDM)
- What an Entity is
- How we can create an EDM from a relational database
- What is the Mapping Tool and what the mappings actually do
- What is the Model Browser
- How we can access relational data through the EDM (with a simplified example) via the source code
- How we can post changes to the relational database through the EDM
Subsequent posts on ADO .NET Entity Framework
As mentioned at the beginning of this post, it is the first in a series of posts dedicated to the ADO .NET Entity Framework and ways of data access through EDM such as Entity SQL (eSQL), Object Services and of course, LINQ to Entities!
In subsequent posts we will have a deeper dive into the Entity Framework and we will see significant features and concepts like: inheritance, entity splitting, complex mapping scenarios, Entity Provider, eSQL, Object Services, LINQ to Entities and much more!
So, check back often for new posts!