When finished, we will see how one of the project references have been included to those related to EF. We are now ready to use the potential of our ORM, as far as development is concerned. We will also see how to carry out an initial database connection and modeling classes, following the two paradigms mentioned above. Database-First Let us first consider the Database-First mode, which - as we said - is mainly directed to the existing database, i.
We recall once again that, at least during the writing of this article, by EF7 onwards, this mode has been suppressed in favor of Code-First and is an important point to keep in mind, when you are going to evaluate the analysis of a solution.
Run the script and we will have few records. Modelling classes with EF Let's see how to model the Visual Studio side, the classes to which we refer in our program to use these data entities.
Once you confirm your choice, Visual Studio will launch the Wizard dedicated to Entity Data Model, so that we can indicate what type of model is used. Our choice, in this case, will be "EF Designer from database ', which realizes the Database-First paradigm. You will be asked to make a connection to our database, press "New Connection" and we will subsequently set the connection parameters. In the following image, an example to adapt to the real development environment is depicted. We will see the generated connection string and we can save it in App.
Finally, we will be asked which entities will arise in the model. In our case, we select the two tables created, leaving the rest of the settings as proposed.
The wizard will complete the operations of the event. It is going to generate a data model that consists of the representatives of the classes of the database entities and showing a graphical representation, on which we can act to create such explicit associations between tables, or change some of the mentioned properties. Important Following the Database-First paradigm, we have already mentioned how the database will provide the framework modeling classes and not vice versa. Therefore, if in this mode we will modify some property and then we will find ourselves in the situation of regenerating the model, these changes - present only on one sideof the code - will be lost, overwritten to that stated on the database.
By browsing in the classes the wizard has created for us, we note two of particular interest, namely hierarchically - are daughters of TechnetModello. Opening them, we will notice that following the structure of the tables to which they refer, exposing the class name as that of the same table and the fields of their counterpart, appropriately converted to the types used in the side code.
FirstOrDefault ; MessageBox. Show art. We perform the Where method on items class, using lambda function that selects the desired item number, returns the first object found by FirstOrDefault method do not operate here validity checks of the data, which of course in a real context must be provided.
At this point, using the art variable, we can refer to its properties and then ask for the issuance of a MessageBox text having equal to DESART properties of art, we get the following output: It is evident that the huge potential of the Entity Framework, which for the developer translates into the factors of primary importance, such as the considerable saving of time and being able to dedicate their efforts to the solution itself, rather than to the intermediate layer between it and the database, which is now fully managed.
Relations between tables, and model consequences In the model, we have determined that the two entities Articles and Families were linked together. In fact, we have not defined Foreign Keys that could have instructed EF how to tie the two tables, which are independent. In this condition, we will have to resort to more elaborate LINQ instructions, which implement the joins, that are missing at the model level.
Suppose we want to select the item ART and we want to expose the screen in the product description rather than that of the same class. Join db. Articoli, performing a Join with db. Famiglie, on the basis of their respective CodFamiglia fields and extracting from that; joins a new object that contains the properties of both. The Where method that accesses the Articles class and makes the selection on Codart field runs on this object, and then returns the first element of the question. Our art variable is now a composite type and we can access respectively to the properties of the part and of the part item's Families: note how in MessageBox there is the description of the article to be emitted, as well as that of the family.
By running a test in the search for the product ART, the displayed result is the following: If we had taken account of this constraint in the design phase, by inserting the Foreign Keys where appropriate, EF would notice it and would be going to create this kind of report automatically. Then we perform a variation on the database structure to see how this affects things in modeling classes. In my app with the divided edmx's we now have some duplicate entities to get the benefit of navigation properties.
Maybe your app has a true separation of domains, but usually everything connects to the user. I'm considering merging two of the now but it will be a lot of work.
So I would say keep them together until it becomes a problem. You should come up with different sets of domain models each containing related objects while each set is unrelated and disconnected from the other one.
Take a look at this post where I explained this matter in detail: Does it make sense to create a single diagram for all entities? How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. There are inherent dangers in the use of any software found on the Internet, and Microsoft cautions you to make sure that you completely understand the risk before retrieving any software from the Internet.
Use mapper resource as xml file. You should know how to code to support this approachs. Consider about if your data is strong type or not. If strong type you should separate database if not you can mix using database. Microsoft will earn lots of money by selling thier SQL Database. Microsoft would say "We will sell millions of database for you!
This looks exactly the approach I am looking for. I had logic like that when I was using ASP. The content you requested has been removed. The generated class will contain objects like User, User1, User2, etc. You can do a few things to make your generated classes more helpful. Open the [YourDatabase]. This contains the template used to generate all the classes for your database tables.
You can do a ton of cool things inside this file to help make your generated classes easier to use. Escape navigationProperty. This summary block is included in the intellisense displayed when you hover over the relationship while typing out code. To summarize, Visual Studio makes working with Entity Framework pretty easy but it still has a way to go. Hopefully this post will help make up for a few of the places it falls short.
0コメント